AERIAL NAVIGATION 
 
 BY 
 
 J. G. W. ^IJNJE VAN SALVERDA 
 
 LATE ADMINISTRATOR OF PUBLIC WORKS OP THE 
 
 NETHERLANDS, AND ADVISORY COUNCILLOR FOR 
 
 HYDROTECHNIC AND RAILWAY AFFAIRS 
 
 TRANSLATED FROM THE DUTCH BY 
 
 GEORGE E. WARING, JR. 
 
 WITH NOTES CONCERNING SOME RECENT DEVELOPMENTS 
 IN THE ART 
 
 NEW YORK 
 
 D. APPLETON AND COMPANY 
 1894 
 
1 if-H 
 
 COPYRIGHT, 1894, 
 BY D. APPLETON AND COMPANY. 
 
 ELECTROTYPED AND PRINTED 
 AT THE APPLETON PRESS, U. S. A. 
 
NOTE BY THE TRANSLATOR 
 
 THE following pages contain a comprehensive sum- 
 mary, mainly in popular form, of the development of 
 aerial navigation from the balloon of Montgolfier (1783), 
 which was filled with heated air, down to the early stages 
 of the investigations and discussions of Langley, Maxim, 
 Holland, and others (1892). 
 
 The writer is a most distinguished Dutch engineer, 
 of advanced age, and now retired from the public serv- 
 ice, in which he held the highest position. 
 
 The conclusions reached by Mr. Fijnje, after his 
 careful review of the whole field, are entirely in the 
 direction of the early successful solution of the problem 
 of mechanical flight, and his conclusions are well sus- 
 tained by his evidence. 
 
 After the publication of the original essay, Mr. Fijnje 
 learned of the investigations of Prof. S. P. Langley, of 
 the Smithsonian Institution, and of the published essays 
 of Mr. Hiram S. Maxim and Mr. John P. Holland, which 
 constituted an important addition to the material avail- 
 able at the time of his first writing. He thereupon is- 
 sued a second pamphlet, describing and discussing the. 
 
 W59018 
 
iv AERIAL NAVIGATION. 
 
 new suggestions as to the application of the aeroplane 
 principle. Copious extracts from this publication are 
 given herein. To bring information as to the progress 
 of the art down to the date of publication, there is pre- 
 sented, in addition to Mr. Fijnje's writings, a resume, 
 with extracts, of Langley's Experiments in Aerody- 
 namics, Holland's essay on Mechanical Flight, and 
 Langley's later and very important paper on The Inter- 
 nal Work of the Wind. 
 
 G. E. W., JR. 
 NEWPORT, R. I., January, 1894. 
 
CONTENTS. 
 
 CHAPTER PAGE 
 
 I. INTRODUCTION 1 
 
 II. THE MILITARY IMPORTANCE OF AERIAL NAVIGA- 
 TION 10 
 
 III. COMPARISON OF BALLOONS WITH BUOYS USED TO 
 
 INDICATE SHIP CHANNELS 23 
 
 IV. THE AIR SHIP IN CALM WEATHER, OR IN THE AB- 
 SENCE OF WIND 32 
 
 V. THE EXTRANEOUS OBSTACLE, OR THE WIND ITS 
 
 ROLE IN AERIAL NAVIGATION .... 40 
 
 VI. PRACTICAL RESULTS ALREADY REACHED IN MA- 
 CHINERY FOR PROPELLING BALLOONS ... 52 
 
 VII. EXPERIMENTS WITH THE BALLOON " LA FRANCE " 
 
 IN THE YEARS 1884 AND 1885 .... 59 
 
 VIII. THE FLIGHT OF BIRDS 64 
 
 IX. THE BOY'S KITE 69 
 
 X. THE ORDINARY FLYING OF BIRDS " ROWING *' 
 
 FLIGHT 73 
 
 XL HOVERING FLIGHT 80 
 
 XII. SAILING FLIGHT 89 
 
 XIII. THE LAW OF AVANZINI 94 
 
 XIV. THE EXERTION OF FORCE BY BIRDS . . .101 
 
 XV. ATMOSPHERIC CURRENTS . . . 104 
 
vi AERIAL NAVIGATION. 
 
 CHAPTER PAGE 
 
 XVI. THE APPLICATION OF THE PRINCIPLE " LE PLUS 
 
 LOURD QUE L'AlR 109 
 
 XVII. CONCLUSION 117 
 
 EXTRACTS FROM A LATER PAMPHLET BY MR. FUNJE . . 125 
 
 PROF. LANGLEY'S EXPERIMENTS 167 
 
 STUDY OF A PRACTICAL AIR SHIP 184 
 
 THE SOARING OF BIRDS AND OF MEN 201 
 
 INDEX , 205 
 
AERIAL NAVIGATION. 
 
 .CHAPTER I. % ., : .--. -,*, 
 
 INTRODUCTION. 
 
 THE important question of aerial navigation has 
 taken on a more and more scientific character, and has 
 enlisted the increasing interest of serious minds. The 
 opinion that a brilliant future is before it is apparent 
 from its very general acceptance among competent ex- 
 perts in France at this time. It is, indeed, slowly, and 
 only within a few years, that it has made real progress. 
 This is to be ascribed in part to recent meteorological 
 observations, and in part to the numerous experiments 
 and photographic observations, with the investigations 
 thereby made possible as to the movements of birds in 
 flying. Such investigations were necessary before the 
 requirements of mechanical flight and the laws con- 
 trolling it could be properly understood. 
 
 The investigation of this question assumed a prac- 
 tical and more especially a military importance during 
 the siege of Paris and in the war of Tonquin. This 
 
2 AERIAL NAVIGATION. 
 
 military side of the problem seems, in France at least, 
 fully to keep pace with the more purely scientific inter- 
 est, which has to do with meteorological problems gen- 
 erally. 
 
 These various trials have led to broader investiga- 
 tions, which must surely aid in the final solution of the 
 difficult problem. ther enlightened countries of Eu- 
 rope and America have also joined in the inquiry. The 
 >more- 6!f 'l&ss Uncertain problem as to the use of air 
 -'brtlS softs; :is still 1 fa'f l .from being solved. The difference 
 is indeed' great when we compare with the present bal- 
 loon the simple one which Joseph Montgolfier sent up 
 on the 5th of June, 1783, at Annonay, and by which 
 he and his brother Stephen made themselves famous.* 
 This balloon was made of varnished paper and was 
 filled with heated air. Nevertheless, the reports of 
 
 * The credit of the invention of the air balloon by the Mont- 
 golfier brothers was not disputed, notwithstanding the fact that 
 already in ancient times mechanical flight had been spoken of. 
 It appears, however, that attention had up to that time been 
 given chiefly to the flight of birds. Reference may be made in 
 this connection to Daedalus and Icarus in Greek mythology ; to 
 the natural philosopher Dante in the latter part of the fifteenth 
 century, of whom it was reported that he flew several times across 
 Lake Trasymene in Italy, till in descending too rapidly he broke 
 one of his legs ; and finally to the smith of Sable, in France, who 
 with a pair of wings was able to descend obliquely, though he 
 could not lift himself through the air. There are, aside from the 
 foregoing, only traditions as to the air ship of Laurent in 1709, 
 and that of the Jesuit priest Lara ; and finally that of the Portu- 
 guese, Guzman, of whom it was maintained that he invented an air 
 balloon in 1736. 
 
INTRODUCTION. 3 
 
 this apparently unimportant experiment were soon 
 spread throughout Europe, and attracted the universal 
 attention of scientific men. Thereupon Prof. Charles, 
 in conjunction with the brothers Kobert, mechanicians, 
 filled the first balloon with hydrogen gas. This was 
 only four metres in diameter. It was sent up from 
 the Champs de Mars in Paris. Rising with astonish- 
 ing rapidity, it soon disappeared from sight and burst 
 from the great expansion of the gas in the lighter 
 upper air. It came down about twelve miles from 
 Paris, in the village of Genesse, where it was de- 
 stroyed with hay-forks and flails by the superstitious 
 
 Five months after the ascension of the air balloon 
 at Annonay the first ascent with passengers was un- 
 dertaken by Pilatre de Rosier and the Marquis d'Ar- 
 lande. They went up at the Chateau " la Muette," not 
 far from Paris, with a balloon fifteen metres in diam- 
 eter, and in twenty-five minutes they came down at 
 about five miles' distance from the starting place. 
 This first trial was soon followed bv several others,* 
 
 * In January, 1885, Dr. R. Joy Jeffries, of Boston, held a pri- 
 vate centennial celebration of an achievement of his grandfather, 
 Dr. John Jeffries, a graduate of Harvard University, who made, 
 in 1785, the first passage by balloon from England to France, 
 with the aeronaut Blanchard, paying him over 700 for the cost 
 of the trip. They quitted the cliff at Dover at quarter past one. 
 At three they passed over the French coast between Cape Blanc- 
 nez and Calais. At quarter past three they descended in the for- 
 est of Guines. The spot is still indicated by a monument erected 
 
4 AERIAL NAVIGATION. 
 
 with such improvements as the safety-valve, the rope 
 net for hanging the car, the use of ballast, the anchor, 
 etc. The idea was then also conceived of determin- 
 ing the elevation by barometrical observations. Prof. 
 Charles and Eobert had already reached a height of 
 six hundred metres in a balloon starting from the gar- 
 den of the Tuileries. When the last named got out, 
 the balloon rose suddenly to a height of three thousand 
 metres, but came down twenty-five minutes later. Gay- 
 Lussac and Biot reached an elevation of four thousand 
 metres, and the first named, alone, an elevation of even 
 seven thousand metres. 
 
 The ascent and descent of balloons could, therefore, 
 be more or less completely regulated ; there was thus 
 far, however, no suggestion of controlling the direction. 
 The question of the buoyancy of the balloon necessary 
 for the ascent still commanded exclusive attention, 
 with the immediate result of giving a wrong direction 
 to observations and to scientific investigations. This 
 led to constant disappointment, and, strictly speak- 
 ing, no further progress in the scientific develop- 
 ment of aerial navigation was made for nearly a 
 century. 
 
 Due account could be taken of the scientific consid- 
 erations only by the aid of 
 
 by the Municipal Council of the city and Compte of Guines. He 
 was much feted, and a very interesting account of the adventure, 
 taken from his journal, is to be found in the Magazine of Ameri- 
 can History, January, 1885, page 66. G. E. W., Jr. 
 
INTRODUCTION. 5 
 
 1. Observations of meteorological phenomena and 
 conditions which, might influence aerial navigation, 
 some of which became possible only after the erection 
 of the Eiffel Tower in Paris. 
 
 2. Observations on the flight of birds, whereby the 
 requirements of artificial flight might be determined in 
 accordance with the laws of Nature. These observations 
 became possible only after the development of instan- 
 taneous photography. 
 
 We could, before that, classify the mechanical work 
 of flight into several kinds of movements, but we could 
 not analyze these nor fully comprehend them. There 
 were, therefore, no sufficient experimental investigations 
 as to the resistance of the air as affecting artificial flight, 
 and for the lack of these requisite means, and of a sci- 
 entific basis for investigation, the development of the 
 art was thus far impossible. As to the flight of birds, 
 and as to the means of making observations concerning 
 this, we worked in obscure uncertainty. This uncer- 
 tainty has been removed only in these later years by the 
 self-registering apparatus and the chronometric pho- 
 tography of Prof. E. J. Marey, of Paris. These marked 
 a new era in the study, and as we watch their results 
 we advance more and more towards the practical end 
 of a knowledge of mechanical flight. The problem has 
 already reached a good measure of development in 
 France, or has at least attracted more and more gen- 
 eral attention ; and though great disappointments have 
 thus far been encountered, we can, on the other hand, 
 
6 AfiRIAL NAVIGATION. 
 
 show the important result that balloons have made us, 
 in a certain measure, independent of gravitation ; that 
 we can, with their aid, be for a time borne up in the 
 air, and that within certain limits we can rise and de- 
 scend. The possibility of moving at all times and in 
 any desired direction is attained only imperfectly, and 
 we have for nearly a century worked in vain towards 
 this end, because of the erroneous supposition that the 
 apparatus must be as light as possible, and that only 
 buoyant balloons can fulfil this condition. Only re- 
 cently it was proved that the object could never be per- 
 fectly attained with balloons, and that in this respect 
 we had simply been following a wrong lead. The 
 means for steering the balloon, which was at first sup- 
 posed to be an unimportant part of the problem that 
 would soon be solved, seems to require the most investi- 
 gation and the most exact knowledge. But few had 
 suspected this, and doubt with regard to it was ascribed 
 to great and unaccountable over-anxiety. Yet this 
 doubt was well founded. 
 
 Among the bold pioneers who have in modern times 
 prepared the way for a scientific study of the problem, 
 Nadar, of Paris, must be accorded the first rank. With- 
 out possessing the varied scientific knowledge requisite 
 for such study which, in fact, at that time was impos- 
 sible he yet arrived, by dint of his own observations 
 and investigations, to the conclusion that the prevailing 
 idea of the necessity of using light balloons was founded 
 in error a conclusion which was pithily expressed in the 
 
INTRODUCTION. 7 
 
 designation of his principle, Le plus lourd que Tair. 
 In order to secure acceptance for that principle, it must 
 be followed out and analyzed, which required not only 
 great outlay but the concurrence of men learned in dif- 
 ferent branches. That point of view had not before 
 been taken, but Nadar became convinced of its neces- 
 sity by mere force of his exceptional common sense, his 
 immovable equanimity, his inspired enthusiasm, and 
 above all his firm conviction, and he was soon recog- 
 nized as the most fit person to awaken a general interest 
 in the universal importance of the object in view. He 
 did not spare himself in the always more or less hazard- 
 ous strife with the powers of the air, and he hesitated 
 even less to make pecuniary sacrifices to his principle, 
 Le plus lourd que Vair, though he brought financial 
 trouble on himself thereby. He was always sustained 
 by his placid, gentle, but courageous wife. 
 
 Nadar set forth his principle in a pamphlet* en- 
 titled Droit au Vol (The Right to Fly). At his own 
 cost he constructed a gigantic balloon, with a capacity 
 of six thousand cubic metres and a height of forty-five 
 metres, trusting therewith to secure the capital, of un- 
 certain amount, which he judged necessary for further 
 exploration. He was fully convinced that his principle 
 could attain general acceptance only after thorough in- 
 vestigation.! It was therefore a great disappointment 
 
 * Published by Iletzel, Paris, four editions, 
 f It should be noted here : (1) That already, in 1837, a Swed- 
 ish engineer, Tollin, had tried to introduce the principle of Le 
 
8 AERIAL NAVIGATION. 
 
 to him that the financial undertaking of " The Giant " 
 was not a complete success.* 
 
 These efforts had only the result of giving his prin- 
 ciple an important bearing on later scientific investiga- 
 tions. Beyond this we can attach no great scientific 
 value to these ascents, which, indeed, they were not in- 
 tended to have. It was always known that the larger 
 the balloon the greater the number of persons that it 
 would support ; that account must be taken of the time 
 available and of the state of the weather ; and that, still 
 more than in ocean navigation, the regulating and start- 
 ing of the balloon demands the services of competent 
 and tried experts. In this regard, the choice of times, 
 and especially of the men in control, was not always 
 
 plus lourd que Tair and (2) Simultaneously with Nadar, Messrs, la 
 Landelle and De Ponton d'Amecourt, in their studies, had ad- 
 vanced the same principle, which resulted in the association of 
 the three men. 
 
 * Nadar made only six ascensions with his balloon, " The 
 Giant," in the years 1864-'67 viz., three times at Paris, once at 
 Brussels, once at Lyons, and once at Amsterdam. Tersteeg joined 
 in the last-named ascent, and wrote a communication concerning 
 it. The balloon was then turned over to a company. The first 
 two ascensions at Paris were made in unfavourable weather; the 
 first time the safety-valve did not close completely, and it became 
 necessary to descend when they had only reached Meaux, five 
 kilometres from Paris ; the second time Nadar was accompanied 
 by his wife and by a descendant of Montgolfier. In coming 
 down they were in danger of their lives, for the balloon, driven 
 by a fierce storm, bounded along the ground with heavy shocks. 
 This account is derived from an accurate report which was soon 
 published in somewhat romantic form, entitled Memoires du 
 Giant, with a preface by Babinet, 1 vol., 12mo, Dentu, 1864, two 
 editions. 
 
INTRODUCTION. 9 
 
 fortunate. The ascent was therefore sometimes a haz- 
 ardous undertaking. 
 
 The principle le plus lonrd que Vair has appeared 
 to me, strictly speaking, not to be entirely sound, for 
 the reason that the weight of the whole apparatus, so 
 far as the conditions for ascent are concerned, need not 
 be heavier than the displaced air ; it contains, however, 
 an unmistakable element of truth, and has helped to 
 do away with a still existing erroneous idea concerning 
 light balloons. It has also led to the conviction that 
 ability to give any desired direction to the flying ma- 
 chine is absolutely necessary. The direction of the 
 common balloon was entirely dependent on the wind ; 
 while the former opinion that the higher strata of the 
 atmosphere moved in an opposite direction, and that 
 advantage could be taken of this fact in the movement 
 of the balloon was not confirmed. The possibility of 
 controlling the direction of air machines has indeed 
 now been established, but thus far only within certain 
 limits ; it is dependent on the nature of the apparatus, 
 on the rapidity of its movement, and on the weight of 
 the machinery employed. I shall endeavour, in the 
 following considerations, to establish this opinion by a 
 general review of the present status of the art, without 
 pretending to a thorough knowledge of its fundamental 
 principles nor of all the details of the subject. 
 
 This would be too extensive a work, and would be 
 beyond my ability. It must, I think, be relegated to a 
 future time, when a more intimate knowledge of the 
 art of aerial navigation shall have been reached. 
 
CHAPTER II. 
 
 THE MILITARY IMPORTANCE OF AERIAL NAVIGATION". 
 
 BEFORE going into the general subject, however, it 
 seems proper to give some attention to the advantages 
 in warfare offered by mechanical flight, which, as has 
 already been observed, has kept pace with the scientific 
 side of the question, and which has led to wider inves- 
 tigation. 
 
 We have in view, in this connection, not only the 
 siege of Paris, but also the war in Tonquin and the 
 recent important military manoeuvres in France.* 
 
 During the siege of Paris the Government was 
 constantly striving to put itself into communication 
 with the departments, and Nadar distinguished himself 
 very greatly in establishing the balloon postal service, 
 rendering his aid in the most disinterested manner; 
 but he had to give way before the extravagant demands 
 as to their personal safety of those employed in the 
 service. 
 
 The state of the weather and the barometrical con- 
 ditions were closely followed day by day, so that the 
 
 * See the Revue du Genie. 
 
MILITARY IMPORTANCE OF AERIAL NAVIGATION. H 
 
 balloons which were sent up came down with much 
 precision. This never failed. As it is not at all my 
 purpose to enter into the political difficulties of the 
 time, I will only say that even Gambetta himself did 
 not hesitate to escape from Paris in a balloon. 
 
 In Tonquin the natives offered a stubborn resist- 
 ance to the French troops under Admiral Courbet. In 
 the low level ground of the delta, that seemed especially 
 designed for rice cultivation, the enemy could deploy 
 en tirailleur, and shield himself behind the smallest 
 clump of bamboo plants, so that he was sufficiently pro- 
 tected, while the French were, on the contrary, exposed 
 to a murderous fire. On the first landing of troops at 
 Kelung they were also confronted in the unknown land 
 by important defensive works of whose existence they 
 had no suspicion. In consequence of the defeat ex- 
 perienced, the French Government found itself obliged 
 to send out strong reinforcements under three generals. 
 At the suggestion of Admiral Courbet, these were ac- 
 companied by a detail of aeronauts, consisting of Cap- 
 tain Aron, Lieutenant Jullien, five subordinate officers, 
 eight corporals, and twenty-three sappers. These were 
 all familiar with ballooning, while the arsenal at Cha- 
 lais provided the needed material.* 
 
 * In this connection it is to be observed that (a) The regula- 
 tion array balloon of six hundred cubic metres could not be trans- 
 ported over the roads then existing in Tonquin, and smaller ones 
 were sent out, which were made in Chalais in less than a fortnight. 
 (b) The hydrogen gas needed for filling the balloon had to be pre- 
 
12 AERIAL NAVIGATION. 
 
 According to the published accounts these balloons 
 answered their purpose excellently well. They accom- 
 panied the troops in all the military operations in Ton- 
 quin, and were also used in action. Not to go too 
 much into details, and confining ourselves to our main 
 purpose, we shall not describe the expeditions and bat- 
 tles, but confine our remarks to some individual in- 
 stances. One of the balloons, after being used unin- 
 terruptedly for thirteen days, was still in sufficiently 
 good condition to allow one observer to make the 
 ascent. 
 
 The outfit had sometimes to be conveyed over sim- 
 ple footpaths, and always over obstructed roads. * By 
 reason of the existence of unusually large bamboo plan- 
 tations, which it was necessary to avoid, they had con- 
 stantly to go through the flooded rice fields. The day's 
 march thus became very difficult, and sometimes, dur- 
 ing strong winds, the men had to tug at the ropes 
 with all their might. No delay was, however, expe- 
 rienced from this source. 
 
 The observations were sometimes made during more 
 or less wind. The balloon then rose to an average 
 height of one hundred and fifty metres, and during 
 
 pared on the ground, (c) It was feared that the varnished balloons 
 would be injured during the transit through the Red Sea. They 
 were therefore loaded not in the hold but on the bridge, near the 
 pilot-house, after being well oiled and covered on the seams with 
 oiled paper. These balloons were not injured in transportation 
 at all, in comparison with those that were left to be varnished on 
 the spot. 
 
MILITARY IMPORTANCE OF AERIAL NAVIGATION. 13 
 
 battles to two hundred and fifty metres. From that 
 height, by raising the voice, it was possible to inform 
 the commanding officer as to the point where the pro- 
 jectiles fell, and as to the strength of the force to be 
 attacked. The commanders acted in accordance with 
 these indications, and thus maintained the courage of 
 the army in a remarkable manner. 
 
 Communications for the chief of staff were written 
 on paper, which was weighted with stones that they 
 might easily be found; these were forwarded immedi- 
 ately by mounted couriers. 
 
 It was also through the exact reconnoitring of the 
 aerial observers that the Chinese were prevented from 
 retiring from Bac-Xinh; and that place was taken 
 without assault and without firing a shot. 
 
 It has therefore occurred to me that a close study 
 of the war of Tonquin in 1884, with an eye to the 
 possible uses of aerial navigation, must be considered 
 as full of importance to the art of war. 
 
 Concerning the use of aerial navigation in the re- 
 cent great military manoeuvres in France, we take the 
 following account from the report of M. Debureaux, an 
 officer of engineers, which appeared in the Revue du 
 Genie. 
 
 According to this officer, the military value of aerial 
 navigation was never so decisively shown as in the ma- 
 noeuvres in the Department of the Aube. Anchored 
 balloons were in telephonic communication with the 
 ground, and the great importance of this novelty was 
 
14 AfiRIAL NAVIGATION. 
 
 fully appreciated. Instead of being obliged to draw the 
 balloon down in order to receive the information that 
 had been gathered, the officers in the car were in con- 
 stant communication with the commanding general, and 
 could keep him always informed of the least movement 
 of the enemy, even those made at a considerable dis- 
 tance. 
 
 The advantages derived were not indeed limited to 
 this. With the new means for making the gas, and with 
 the improved method for filling the balloon, they were 
 able to make the ascent within an hour, and could trans- 
 port the balloon, whether filled or not, with the required 
 aerostatic material without the least difficulty. This 
 material was moved from Versailles to Brienne, more 
 than one hundred and twenty miles distant, in ten days' 
 march. They sometimes made more than twenty-five 
 miles in a single day. It was found in practice, how- 
 ever, that the regulation number of men was not suf- 
 ficient, and that the party was exposed to much too 
 great fatigue, so that their number was more than 
 doubled. 
 
 The first ascent was made in rain and wind, and 
 under generally difficult and uncomfortable conditions, 
 at the battle of Aulnay. 
 
 The aerostatic park had to be conveyed to Garenne, 
 the place fixed for the ascent, over hilly and muddy 
 roads. In spite of these difficulties, however, the ascent 
 was made at the appointed hour, and great service was 
 rendered. Warning was immediately given to the com- 
 
MILITARY IMPORTANCE OF AERIAL NAVIGATION, 15 
 
 mander of the Eighth Army Corps that he was moving 
 his lines against a mere feint, and the position of the 
 reserve and the real line of attack were pointed out to 
 him. Thereupon four general officers got into the bal- 
 loon to profit by the most important advantages that the 
 position offered. 
 
 General Galiffet, at Colombey, remained two hours 
 and a half in the car, and from there, at an elevation of 
 from two hundred and fifty to four hundred metres, 
 gave his orders by telephone. The army then covered 
 a field eight miles long by from two to six miles wide. 
 The commander of the Western army was, neverthe- 
 less, enabled closely to follow the movements made by 
 the enemy in preparation for the battle; he could 
 clearly distinguish all objects and thus decide how to 
 place his artillery. He could study the country for a 
 distance of twelve miles as on a map, and from the 
 rising dust could follow the movement of troops con- 
 cealed by woods. After leaving the balloon, this gen- 
 eral remained in constant communication with the 
 observers. 
 
 At Vendeuvre, the cavalry fight, more than nine 
 miles distant, was signalled to General Davoust. Dur- 
 ing the night engagement on the Voire the balloon 
 showed itself to be most serviceable. On the other 
 hand, it was thought at Margeris that it was not best 
 to risk the outfit during the stormy weather. In 
 actual war this consideration would not be allowed to 
 have weight. 
 
16 AfiRIAL NAVIGATION. 
 
 The transportation of the filled balloon was most 
 successful, even in the midst of a fight and in spite of 
 the crowding of the troops at the passing of Bar-sur- 
 Aube ; in the march through the forest of Bassicin and 
 the Great Eastern Woods, there was, in like manner, no 
 disturbance of the movement of the troops. Every ob- 
 stacle was overcome in from two to five minutes, while 
 the balloon could always be brought at a trot with great 
 precision and at any moment to its place in the column. 
 
 The last trial was at a review of the troops at Vitry. 
 The balloon was sent up after the aerostatic park had 
 been moved into its place, and hovered at a height of 
 six hundred metres over the magnificent display af- 
 forded by an army of one hundred thousand men on 
 the march. 
 
 In concluding his report, M. Debureaux observes 
 that, had Napoleon at Waterloo and Bazaine at Saint 
 Privat had a balloon service at their disposal, a different 
 result might have been expected from both of these bat- 
 tles ; the approach of Bllicher in the first place, and in 
 the latter the small force of the Germans, would have 
 been known. 
 
 M. Debureaux thinks also that at a distance of three 
 miles the balloon would have been beyond the reach of 
 artillery, and that it would have commanded the ground 
 for a distance of more than six miles. Even at night 
 the country is sufficiently illuminated to be compared 
 with a map. He commends also the ability to trans- 
 port the balloons over routes which are removed from 
 
MILITARY IMPORTANCE OF AERIAL NAVIGATION. 17 
 
 the immediate scene of action, and is further of the 
 opinion that, by reason of the facility with which they 
 may be transported, they may be placed beyond the 
 reach of fire, their information being communicated by 
 telephone. The balloon may soon be of great service 
 in sieges, for it can be flown quite over the invested 
 place and descend beyond the reach of danger, report- 
 ing to the besieging army what is going on in the town. 
 
 From the experience obtained by the ascent at Vitry, 
 such an expedition may be made with a loss of only 
 three hundred and fifty pounds of ballast. 
 
 Finally, it is to be expected that with a portable 
 outfit a buoyant balloon can be brought into use within 
 half an hour of the arrival of the aerostatic park, and 
 the foregoing account shows what services can be ren- 
 dered. In the Netherlands, so far as I know, aerial 
 navigation has engaged attention only from a military 
 standpoint. At Utrecht experiments have been made 
 with a balloon constructed after an old model which 
 cost ten thousand florins, each trial costing seventy 
 florins. 
 
 The conclusions reached were, that it was difficult in 
 a covered or wooded country to distinguish the move- 
 ment of troops and to learn their purpose. As will be 
 shown later, the experience at Atjeh was of a similar 
 character. 
 
 The possibility of applying aerial navigation to mili- 
 tary ends was thus also realized in our own country, 
 but its technical development had not been sufficiently 
 
18 AERIAL NAVIGATION. 
 
 advanced for its place in the make-up of the army and 
 in measures of defence to be definitely indicated. It 
 was also thought that, in view of its great cost, its im- 
 mediate development would not be justified while so 
 many things, which in the opinion of experts were 
 more necessary as means for our defence, must be 
 provided, and which, for lack of means, still remain 
 wanting. 
 
 The Military Department, which appreciated the 
 importance of the subject in the Netherlands, was 
 familiar with the work at Chalais, and with the estab- 
 lishment of the balloon service in the French, German, 
 and Austrian armies. There was even prepared a plan 
 for an organization of the service, according to which 
 the cost of the plant with eight balloons amounted to 
 three hundred thousand florins, while it was estimated 
 that for their proper service there would be required 
 nine officers, sixteen non-commissioned officers, and 
 four men ; and for the transportation of the park, ten 
 sergeants, ten corporals, sixty-eight riders, and one 
 hundred and sixty-eight horses ; and for the service of 
 the arsenal, one engineer, one stoker, three labourers, 
 one mechanic, one tailor, and one sail-maker. 
 
 The cost would thus not be unimportant ; it seems 
 to justify the fear that such an addition to the military 
 budget would not be acceptable to the States-General. 
 It would seem judicious to leave these costly experi- 
 ments to the great powers, and to let smaller states 
 ultimately make use of their results. We should, how- 
 
MILITARY IMPORTANCE OF AfiRIAL NAVIGATION. 19 
 
 ever, keep ourselves constantly informed as to the latest 
 development of the art, whether at Chalais and in the 
 French army or elsewhere, in order at least to be pre- 
 pared for a time of better financial conditions. AYe 
 should not let our thrift get the better of our wisdom. 
 We should keep to the idea of establishing a balloon 
 service at least for the protection of the necessary force, 
 against the time of need, and it is not advisable to 
 postpone this until the emergency arises not to await 
 the threat of war. 
 
 The thought suggests itself that when, before At- 
 jeh, we were seeking in every direction for the means 
 of success, how much better the situation would have 
 been there had we appreciated the value of exact recon- 
 naissance by means of anchored balloons ; and, on the 
 other hand also, that the utility of balloons was not 
 at all realized in Atjeh, because the position of the 
 enemy's front stretched along the fortifications and was 
 thickly overgrown with cocoa-trees, or lay in other cov- 
 ered ground. It was thought that even if the balloon 
 should have reached the required elevation, nothing 
 could be seen but a mass of tree-tops, under which the 
 movements of the enemy would remain concealed. 
 
 Nevertheless, a foreigner, probably an Englishman, 
 undertook to make observations. He was, however, 
 not successful in his undertaking. His balloon met 
 with a collision at the first trial, and thus soon became 
 unserviceable. It was repaired after much trouble and 
 delay, encountering difficulties for a time, but finally it 
 
20 AERIAL NAVIGATION. 
 
 was possible to send it up. When it had risen to a cer- 
 tain height, they saw under them a mass of verdant 
 islands, among which the enemy had taken up his po- 
 sition. 
 
 As a matter of fact, nothing could be seen of the 
 enemy himself, so that the experiment with the an- 
 chored balloon was considered a failure and its use was 
 discontinued. Had they not become discouraged, and 
 had means been found in Atjeh to keep the balloon in 
 good condition, the experiment would probably have 
 been carried to a better result. Still, it was generally 
 considered that it was not possible to observe much 
 through the green foliage, and, for this reason, little 
 practical utility was expected from ballooning in Atjeh. 
 I do not consider myself competent to dispute this 
 opinion. I therefore allow myself only to suggest the 
 question whether this impediment could not have been 
 removed by the burning or the cutting of the wood, at 
 least in part, and whether it also existed in the case of 
 the coast blockade. After the recent great military 
 manoeuvres in France, in which the reconnaissance was 
 so complete and covered such distances, it seems to me 
 that there can at least be no doubt as to the utility of 
 balloons for military .purposes in the Netherlands and 
 in India, nor that this utility will increase with ad- 
 vances in the science. 
 
 Still, however this may be, the difficulty if. not the 
 impossibility of distinguishing an enemy scattered un- 
 der cocoa trees or other wood cannot be denied, and the 
 
MILITARY IMPORTANCE OF AfiRIAL NAVIGATION. 21 
 
 difficulty cannot be considered slight. I should not, 
 however, venture to maintain that if the trial had been 
 made with suitable apparatus in place of an imperfect 
 balloon, and with well -trained men, no better result 
 would have been reached. It may very well be that, 
 under the conditions existing, it would have been better 
 not to make the trial at all. This opinion seems to 
 be confirmed by the results obtained in Tonquin. It 
 should be remembered, also, that the conditions of the 
 ground differed too widely for a positive opinion con- 
 cerning this case to be expressed, and I am bound 
 to defer to the opinion of those who are more com- 
 petent. 
 
 Indeed, if aerial navigation is to become generally pos- 
 sible in the future, we must learn to take exact account 
 of the various situations and conditions under which it 
 is to be effected. These differ materially from those 
 encountered in navigating the water, where obstacles 
 of no less importance had to be contended with. Yet 
 we can now look back on those obstacles with compla- 
 cency, for they have been slowly and more and more 
 completely overcome, and the same may be assumed 
 in the case of mechanical flight. Without underrating 
 in the least the great services of so many who had al- 
 ready aided more or less in the solution of the important 
 problems, it seems to me that Commandant Eenard 
 followed out the difficulties and the requirements of 
 the art in the most exact way. By his analytical 
 development of the principles upon which mechanical 
 
22 AERIAL NAVIGATION. 
 
 flight must depend, he gave practical form to his ob- 
 servations, on which others can base further investiga- 
 tions and experiments. We shall, therefore, in the fol- 
 lowing observations, make use of his communications.* 
 
 * La Navigation Aerienne, par M. le Commandant Renard i 
 Revue de V Aeronautique, Theorique et Applique, Premiere Annee, 
 1888, Paris, G. Masson, editeur, Boulevard Saint-Germain, 120. 
 
CHAPTER III. 
 
 COMPARISON OF BALLOONS WITH BUOYS USED TO 
 INDICATE SHIP CHANNELS. 
 
 IN the effort to set forth the conditions under 
 which aerial navigation must take place, the first air 
 balloons of Montgolfier have frequently and not alto- 
 gether improperly been compared with harbour and 
 river buoys a comparison which is, to a certain extent, 
 reasonable. Both objects maybe regarded as floating, 
 inert bodies, which follow the impulse of the changing 
 current. The resemblance is, however, limited to this 
 condition. The buoy, if carefully constructed, floats in 
 the water for an unlimited time, while the balloon, on 
 the other hand, cannot maintain its position in the air 
 and continue to float without the constant intervention 
 of the aeronaut. 
 
 The comparison is, therefore, justified only if we 
 conceive of an anchored buoy floating entirely sub- 
 merged beneath the surface and rising or falling in the 
 water under the least accidental impulse. To transform 
 an air buoy into an air ship or balloon, its constant sta- 
 bility must be assured. This is, in the first place, im- 
 
24: AERIAL NAVIGATION. 
 
 possible, and, in order to form a correct idea concerning 
 it, it is necessary to suppose a buoy not floating on the 
 surface of the water, but so ballasted that its own weight 
 is the same as that of the water which it displaces. Were 
 it, under these conditions of equilibrium, placed at a suf- 
 ficient depth in the water, it would maintain its position 
 without the least tendency to rise or to sink. When, how- 
 ever, by the accumulation of barnacles or other matters, or 
 in consequence of other incidental causes, its weight in- 
 creases and becomes greater than that of the displaced 
 water, then will the buoy slowly settle to the bottom. 
 The density of the water, which is practically incom- 
 pressible, is about the same at all depths, so that the 
 weight of the displaced water will hardly increase as the 
 buoy sinks. Should the weight of the buoy become in 
 any way lessened, then, by the same token, it would rise 
 to the surface, while it can have no stable position when 
 entirely surrounded by water. This instability of a com- 
 pletely submerged object was always a difficulty in the 
 case of submarine vessels, which are constantly exposed 
 to the danger of going to the bottom of the ocean in re- 
 sponse to an increase of their weight from any cause. In 
 this connection the movement of fishes is worthy of at- 
 tention. These are perfectly provided with means for 
 overcoming this instability, and maintaining any desired 
 position by the unconscious use of effective mechanical 
 means. 
 
 By imitating the methods of fish, submarine vessels 
 have recently been made relatively stable, but they are 
 
COMPARISON OF BALLOONS WITH BUOYS. 25 
 
 still far from satisfactory, and they are not at all to be 
 compared with the strongly driven ships which sail over 
 every sea. Had we thus far brought into use only sub- 
 marine vessels, navigation would probably still be in the 
 first stages of its development. A similar difficulty will 
 be experienced in aerial navigation, because air ships and 
 the means provided for their propulsion are completely 
 immersed in the fluid air. Just as the submarine vessel 
 moves in the water, so must the balloon move in the 
 atmosphere ; both are subject to the same conditions of 
 instability. 
 
 The properties of the two fluids, water and air, are 
 in fact very different. Air is not, like water, incom- 
 pressible, so that its density, and consequently its spe- 
 cific gravity, decrease with the elevation, and its origi- 
 nal buoyant force, however great it may have been, 
 ceases and disappears at a certain height, or rather is 
 there in equilibrium with the balloon. Therefore, at 
 this elevation, the balloon is brought to a standstill, 
 but on any accidental increase of weight it falls far 
 enough to bring it again into equilibrium with the dis- 
 placed air. 
 
 This condition appears to be indisputable, and in- 
 deed must be so were the balloon air-tight, and made, for 
 example, of steel plates, so that its volume would re- 
 main the same at all elevations. This, however, is not 
 the actual condition. The envelope must be opened on 
 the under side, for without this precaution the rising 
 balloon must burst as it passes into air of less and 
 
26 AfiRIAL NAVIGATION. 
 
 less pressure, and the confined gas expands in conse- 
 quence.* 
 
 A balloon of constant weight or volume, and capable 
 of maintaining a fixed position, is therefore impracti- 
 cable. We must, on the contrary, consider it as a bag 
 filled, or partly filled, with gas, and which will yield 
 freely to the changes of volume of this gas as it con- 
 tracts in falling or expands in rising. Or that by 
 the use of a very sensitive safety-valve the gas will be 
 allowed to escape freely. This last precaution is im- 
 peratively needed when the balloon, originally relaxed, 
 has become entirely full, and further expansion has be- 
 come impossible. 
 
 Disregarding the condition just named, and taking 
 account only of the state of equilibrium which must ex- 
 ist whenever a balloon, under ordinary circumstances, 
 is not entirely filled, and is free to expand and contract, 
 then the pressure of the outer air and that of the gas 
 remain the same, and both constantly maintain equal 
 density. 
 
 Let us suppose further, for the sake of simplicity, 
 that the partly filled balloon contains one kilogramme 
 of ordinary commercial hydrogen gas, the weight of 
 which bears to that of the atmosphere the proportion of 
 
 * It is estimated that a common silk balloon, with a diameter 
 of ten metres, completely filled with hydrogen gas at the level of 
 the sea and tightly closed, will burst at a height of four to five 
 hundred metres, and that to reach this elevation it is necessary to 
 reduce the ballast by sixty or seventy pounds. 
 
COMPARISON OF BALLOONS WITH BUOYS. 27 
 
 1 to 6-J. Then, so long as the balloon is not fully dis- 
 tended, this quantity of gas will always, at any eleva- 
 tion, displace 65 kilogrammes of air; therefore the 
 result must be, according to the law of Archimedes, that 
 the balloon will tend to rise with a force of 5 -5 kilo- 
 grammes, according with the difference in weight of the 
 displaced air and that of the gas. 
 
 This force is independent of the elevation reached. 
 A balloon so provided with ballast as to be in equi- 
 librium at a given height will therefore, below this 
 height, be under the same conditions with a buoy sub- 
 merged in the ocean, and thus, on any escape of gas or 
 discharge of ballast, must rise or fall. This shows how 
 difficult it is to convert such a constantly vacillating ob- 
 ject into an air ship.* 
 
 * The instability of the partly filled balloon can be thus illustra- 
 ted : Suppose that one cubic metre of ordinary hydrogen gas be in- 
 troduced into a balloon of several metres' capacity at the level of 
 the sea, and that we may disregard the relatively slight weight of 
 the envelope. The weight of this one cubic metre of gas is 0*2, 
 and that of the air 1-3 kilogramme ; the difference of 1-1 kilo- 
 gramme constitutes the lifting force of one cubic metre of gas at 
 the level of the sea ; this is, therefore, the lifting force of the bal- 
 loon. Now, let this balloon reach an elevation of fifty-five hun- 
 dred metres that is to say, the zone where the pressure of the air 
 is reduced one half then, according to the law of Mariotte, (a) 
 the volume of the gas is doubled, and amounts to two cubic me- 
 tres ; (6) the specific gravity of the air is reduced to one half, and 
 
 so amounts for 1 cubic metre to ^ x 1'3 kilogr., or 0'65 
 
 that of the gas, also reduced to -, being | x 0*20 kilogr., or (HO 
 so that the lifting force per cubic metre is reduced to. ... 0*55 
 or one half of its value at the sea level. 
 
 We have therefore, at this height, twice the original volume 
 
23 AftRIAL NAVIGATION. 
 
 When an imperfectly filled balloon rises and its gas 
 expands, it becomes first completely filled and then a 
 portion of its contents escapes through the safety-valve, 
 and the weight of the gas contained in the balloon 
 grows less with the necessary result of an increase of 
 buoyancy, which is in a constant relation to the weight 
 (5 '5 times with ordinary gas). The balloon thereby be- 
 comes restricted in its movement and soon comes to a 
 standstill. For a correct conception of this supposition, 
 it is to be understood that it is not the weight but the 
 volume of the balloon that remains the same, and that 
 for the sake of simplicity it is assumed to have been 
 filled with one cubic metre of hydrogen gas. The 
 weight of this one cubic metre of gas at the sea level is 
 equal to 0*2 kilogramme, and that of one cubic metre 
 of air to 1-3 kilogramme; so that the lifting force of 
 each cubic metre of gas at this level is equal to 1/3 
 0-2 = ri kilogramme. After the rising of such a bal- 
 loon to a height of fifty-five hundred metres, the weight 
 of the air and of the gas is only one half of their weight 
 at the sea level, and consequently their difference of 
 lifting force is correspondingly diminished at this 
 height : 1-1 2 = 0-55 kilogramme. Were the bal- 
 loon, therefore, so ballasted that its lifting force at the 
 
 of gas ; but each cubic metre has one half of the original lifting 
 power, so that the whole force remains the same. 
 
 This illustration is applicable to all heights, whenever the bal- 
 loon is not entirely filled and the gas in the envelope can swell or 
 shrink. 
 
COMPARISON OF BALLOONS WITH BUOYS. 29 
 
 sea level was only O55, then this force would be ex- 
 hausted at the elevation of fifty-five hundred metres, 
 and the balloon would there come to a standstill. In 
 other words : it would there have reached its zone of 
 equilibrium, and in general if a balloon filled at the 
 sea level has one tenth, two tenths, three tenths, etc., of 
 its lifting force discharged, it will reach the level where 
 the atmospheric pressure is reduced by one tenth, two 
 tenths, three tenths, etc. The elevations above the sea 
 that will be reached by a balloon of one thousand cubic 
 metres' capacity by such reduction of ballast are given 
 in the following table : 
 
 T\7_ __ 1 L J. 
 
 Pressure of 
 
 
 
 vv eignt 
 
 the air, the 
 
 Corre- 
 
 
 or t lit* 
 discharged 
 ballast, kilo- 
 
 pressure at 
 the sea level 
 being the 
 
 sponding 
 elevation, 
 metres. 
 
 Remarks. 
 
 grammes. 
 
 unit. 
 
 
 
 
 
 1-0 
 
 
 
 The third column shows the 
 
 110 
 
 0-9 
 
 800 
 
 height which a balloon of 
 
 220 
 
 0-8 
 
 1,800 
 
 1,000 cubic metres capacity, 
 
 330 
 
 0-7 
 
 2,900 
 
 filled with common gas, 
 
 440 
 
 0-6 
 
 4,100 
 
 would reach with the dis- 
 
 550 
 
 0-5 
 
 5,500 
 
 charge of the amount of bal- 
 
 660 
 
 0-4 
 
 7,300 
 
 last given in the first column. 
 
 770 
 
 03 
 
 9,600 
 
 There may be average varia- 
 
 880 
 
 0-2 
 
 12,800 
 
 tions of 50 metres, due to 
 
 990 
 
 0-1 
 
 18,300 
 
 difference of atmospheric 
 
 1,100 
 
 o-o 
 
 Uncertain. 
 
 pressure. 
 
 The rising of a full balloon will be, as shown in this 
 table, in proportion to its decrease in weight, and the 
 zones of equilibrium will be as shown in the third col- 
 umn. Between these zones of equilibrium and the 
 earth the balloon is necessarily relaxed and conse- 
 
30 AfiRIAL NAVIGATION. 
 
 quently unstable, so that by the least increase of weight 
 it would sink to the earth, and by the least decrease of 
 weight would rise to its zone of equilibrium. 
 
 This increase and decrease of weight occur con- 
 stantly during the flight of the balloon. The force of 
 the sun's rays, dampness caused by rain, snow, hail, 
 etc., clouds, the unavoidable escape of gas, and many 
 other causes, constantly disturb the delicate equipoise 
 of the balloon, which can be maintained at a given 
 height only by the constant intervention of the aero- 
 naut. 
 
 As to the means by which this end is to be secured, 
 we do not yet know the first principles. Still, there are 
 means always available to counteract these accidental 
 variations of the buoyancy of the balloon, as by throw- 
 ing out ballast and letting a certain quantity of gas 
 escape. However complete these means may be, they 
 have the great drawback that the ballast is soon ex- 
 hausted, and the balloon, weakened by loss of gas, can 
 only settle lower and lower down as local causes present 
 themselves which increase its weight. This explains 
 the short duration of the flight in the air, and equally 
 of ascents made with completely impervious balloons. 
 
 The balloon cannot, therefore, be compared in any 
 way with a vessel floating on the water. It is rather an 
 unstable buoy, which, even if its movements could be 
 controlled, could not be of much service, because it can 
 remain only a few hours afloat. 
 
 That we are now, however, becoming more and 
 
COMPARISON OF BALLOONS WITH BUOYS. 31 
 
 more capable of coping with this difficulty, and that 
 we shall be able completely to overcome it, cannot in 
 the least be doubted. We already have at command 
 powerful motors of little weight, and we need only 
 combine these with propellers in order to create a 
 strong movement in ascending or descending. It is 
 only necessary for the aeronaut to give the proper 
 direction in order to keep his apparatus in equilibrium. 
 It seems as though accidental variations of buoyancy 
 had already been completely provided against. These 
 means, however, did not exist at the time of the inven- 
 tion of the balloon, and this of itself was enough to 
 render fruitless every effort of the aeronauts to steer 
 their balloons or to maintain their equilibrium; and 
 though this may now be considered quite possible, there 
 are still difficulties connected with it which are not to 
 be foreseen. 
 
CHAPTER IV. 
 
 THE AIR SHIP IN CALM WEATHER, OR IN THE ABSENCE 
 OF WIND. 
 
 WE have thus far considered the balloon only as a 
 floating mass, whose form has not been taken into the 
 account. This is no longer sufficient. In place of the 
 spherical " buoy," which is familiar to all, we now have 
 the various forms indicated by the terms "air ship" 
 or "flying machine," which are provided with motive 
 power and with means of propulsion, such as a screw 
 or oars. In order clearly to understand the conditions, 
 let us suppose that the air above the earth is completely 
 motionless, or without wind. From this simple condi- 
 tion we shall be able to go on to those of greater com- 
 plexity. 
 
 In this air ocean suppose there to be placed a float- 
 ing machine in complete equilibrium, and controlled 
 by a strong oarsman with two light oars shaped like 
 rackets. These will be so handled that the stroke is 
 made with the broad side toward the air and the re- 
 turn with the edge, in order that the forward move- 
 ment may not be retarded by the return stroke. This 
 return must produce the same phenomenon that is pro- 
 
THE AIR SHIP IN CALM WEATHER. 33 
 
 duced in the water, and even a spherical balloon must 
 yield more or less to the efforts of the oarsman. It is 
 clear, however, that it will move more rapidly if it is 
 given the elongated form of a boat or a fish, and that 
 the shape of the common balloon is the most unfavour- 
 able. Hence the more recent adoption of elongated 
 constructions in the classic form of a fish or a cigar. 
 
 It is to be noted, in this connection, that very soon 
 after the first appearance of the balloon this elongated 
 form was tried, and that attention was then given to its 
 steering. We shall here, in the main, adopt this form, 
 and assume accordingly a cigar-shaped flying machine 
 with a car furnished with a propeller or with a crew 
 of oarsmen. On the operation of these propellers or 
 oars the whole apparatus must move forward like a 
 boat. If also provided with a rudder, it may be turned 
 in any direction and carried to any elevation above the 
 earth, because it is assumed that the air is in a condi- 
 tion of rest, and the ship is therefore floating in an air 
 ocean in which all movement is arrested. 
 
 The theory of aerial navigation is in this case a 
 simple one, as it is sufficient for the direction of the 
 balloon that its form should be elongated and that 
 it should have a rudder. Furthermore, the oarsmen 
 might be replaced by some kind of motive power by 
 which greater force may be applied without a change 
 of weight, and greater speed secured without the ne- 
 cessity of modifying the ordinary operation of the 
 system. The speed that may be attained in a calm ap- 
 
34: AERIAL NAVIGATION. 
 
 pears, according to computation and experiment, to be 
 less than that which ordinary boats have indicated as 
 possible. It is true that in recent trials with the flying 
 machines at Chalais (Mendon) a spsed was reached of 
 6-5 metres per second equal to about fourteen miles 
 per hour but this required a much higher power than 
 would be applied to an ordinary boat of the same size. 
 
 However this may be, the great question might be 
 considered to be solved by this speed, if only the con- 
 dition could be granted that the air above the earth 
 should remain without movement. This, however, is 
 not possible, and the great difficulty of the problem is 
 due to the resistance of the wind. We shall recur to 
 this later, confining ourselves for the present to indi- 
 cating the inherent difficulties peculiar to this form 
 of balloons, which are really formidable, and which 
 nearly caused the death of Henri Giffard. This diffi- 
 culty results from a tendency of the balloon to swing 
 from end to end because of its elongated form. It is 
 very different from the instability already referred to, 
 which causes balloons of all forms constantly to rise 
 and fall. It is the inclination to swing or pitch from 
 front to rear, very much as a ship heaves. 
 
 This peculiarity is called longitudinal instability. 
 
 In order to understand this, let us assume, with Du- 
 puy de Lome, that the balloon, after having reached its 
 zone of equilibrium, has fallen a little, and as a conse- 
 quence its content of gas has contracted, and that the 
 envelope has consequently become somewhat relaxed. 
 
THE AIR SHIP IN CALM WEATHER. 35 
 
 From this moment, as soon as it inclines a little for- 
 ward, the gas, following its tendency to rise, moves 
 toward the rear end and increases its elevation, so that 
 the inclination is increased. If the person in charge 
 now attempts by any means to restore the proper posi- 
 tion, and goes a little beyond the mark, the gas will 
 move more or less suddenly to the front, and the bal- 
 loon will slope in the opposite direction. In 1855 such 
 an elongated balloon, in which Henri Giffard was de- 
 scending, pitched to such a degree that, as it reached 
 the ground, it broke loose from its net with such force 
 that it burst, and fell at some distance in two separate 
 parts. Thus we see that even in calm weather we have 
 to contend with a difficulty which may attach to pro- 
 pelled balloons, and which the early experimenters 
 could not suspect. Recognizing this difficulty, how- 
 ever, Dupuy de Lome was, by his observations and ex- 
 periments, enabled to overcome it with the modern 
 balloon of slight elongation. 
 
 The means applied by this excellent engineer were 
 of two kinds : The first lay in maintaining a constant 
 extension of the envelope by introducing air in pro- 
 portion as the gas contracted. As, however, the mix- 
 ture of air with the gas is not easy to accomplish, 
 Dupuy de Lome, following the example of General 
 Meusnier, introduced into his balloon a smaller one 
 filled with air for filling the place left by the con- 
 tracted gas. A double purpose was hereby accom- 
 plished : in the first place, the constant filling of the 
 
36 
 
 AfiRIAL NAVIGATION. 
 
 balloon was secured, so that it could fly through the air 
 as a stable body ; and, in the second place, the possibility 
 of the movement of the gas from one end to the other 
 was decidedly checked, which contributed very effec- 
 tively to its stability. 
 
 The second means consists in the manner of hang- 
 ing the car to the balloon * so that they were inflexibly 
 bound together. 
 
 This is illustrated in the accompanying Figs. 1 and 
 2, where the balloon is indicated by the line A B, and 
 the car by the line P Q. By suspending the car from 
 
 FIG. 1. 
 
 FIG. 2. 
 
 the points A and B with the cords or hangers A P, B P, 
 A Q, and B Q, the displacement of the points P and Q is 
 
 * This method of hanging was not, indeed, original with Dupuy 
 de Lome. It was already known in America and in France. 
 
THE AIR SHIP IN CALM WEATHER. 37 
 
 held within certain limits, and sufficient stability of the 
 whole is secured by the simple use of common ropes. 
 
 The rigidity thus secured must very materially steady 
 the air ship lengthwise, so that the tendency to take an 
 inclined position is much better counteracted by the 
 arrangement shown in Fig. 1 than by that shown in 
 Fig. 2. 
 
 It appears from the foregoing observations that cor- 
 rect ideas have been formed as to ballooning in calm 
 weather, and that, leaving out of the consideration the 
 question of stability of position in relation to the eleva- 
 tion attained, we must, in order to bring a balloon under 
 control 
 
 1. Give it an elongated form comparable to that of 
 ordinary boats. 
 
 2. Insure the constancy of its shape by means of a 
 small balloon placed inside of the large one, which will 
 replace the contracted or escaped gas with atmospheric 
 air. 
 
 3. Increase the longitudinal stability resulting from 
 the use of this small balloon by attaching the car, by 
 means of a rigid support, with triangular meshes. 
 
 4. Introduce a means of propulsion of suitable di- 
 mensions, combined with a motor, which shall have the 
 maximum of power with a minimum of weight. 
 
 5. Establish at the rear end, as in ordinary vessels, a 
 rudder by which the direction of the movement can be 
 controlled. 
 
 With these means the question of aerial navigation 
 
38 AfiRIAL NAVIGATION. 
 
 in its simplest form, and in cairn weather, may be re- 
 garded as already solved. Thus far its general prin- 
 ciples do not differ from those of ordinary water navi- 
 gation. 
 
 That the problem is still incompletely solved, that it 
 requires the creation of new and as yet unknown appli- 
 ances, must not be ascribed to the peculiar properties 
 of the atmosphere, but to another well-defined cause 
 namely, the wind, which we can neither avoid nor mod- 
 ify, and which, even in sailing a ship, we are obliged to 
 contend with and counteract. By wind we must under- 
 stand the moving of a stratum of air with relation to 
 the earth, or, for the aeronaut, a movement of the earth 
 with relation to the stratum in which he finds himself, 
 because the balloon must be considered as belonging to 
 this. 
 
 It is worthy of remark that wind considered as a 
 motive power does not exist for the aeronaut, that it 
 cannot be felt or observed by one who is immersed in 
 the moving air, and that it cannot in the least disturb 
 the equilibrium of the balloon.* It has for the aeronaut 
 only the practical and important result that the earth 
 moves under his feet with the velocity of the wind, and 
 
 * The velocity of the movement of the surface of the earth due 
 to its daily revolution about its axis is equally little felt, because 
 no power can be derived from it, and the free movement of the 
 living beings and objects upon it cannot be disturbed thereby. 
 The same phenomenon is to be observed in the case of carriages, 
 steamboats, and trains. 
 
THE AIR SHIP IN CALM WEATHER. 39 
 
 in its passage mountains, towns, cities, and villages, and 
 even the place which he desires to reach, are carried with 
 it. The navigation of the air in calm weather has, as it 
 were, an attainable fixed object ; practical aerial naviga- 
 tion has, on the contrary, the movable aim of the flight 
 of birds. 
 
CHAPTER V. 
 
 THE EXTRANEOUS OBSTACLE, OK THE WIND ITS 
 HOLE IN AERIAL NAVIGATION. 
 
 THE part that the wind plays in aerial navigation 
 has added greatly to the difficulty of solving the prob- 
 lem. It seems to me also not thus far to be generally 
 well understood and it becomes desirable that it should 
 be more closely studied. 
 
 What we understand as wind manifests itself on the 
 earth by the exertion of force which we call wind 
 power, violence, etc. In this view there is, indeed, for 
 the aeronaut, no such thing as wind. It exists for him 
 only as a source of motion which, at a given moment 
 and within the limits of the horizontal stratum in 
 which he is floated, is to be regarded as straight and 
 uniform. 
 
 If the balloon is, however, bound to the earth by 
 one or more ropes, or anchored, then he feels, like every- 
 thing else that is bound to the earth, the amount and 
 force of the wind. For this reason an ascent in an 
 anchored balloon is sometimes dangerous and always 
 unpleasant. 
 
 If, however, the bonds are broken which attach it to 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 41 
 
 the earth and the balloon is allowed to rise in the air, 
 its natural element, then the most severe shocks are 
 quieted in a few moments and are followed by com- 
 plete calm. The balloon, carried along by the storm, 
 seems to be immersed in a layer of still air, or in the 
 atmospheric ocean. The smoke of a cigar would, if 
 smoking were permitted, rise vertically, while the trees, 
 hundreds and perhaps thousands of metres below, are 
 bending under the force of the wind, and the ships on 
 the sea are braving the wild elements in great danger. 
 The correctness of this illustration will be readily ac- 
 cepted, and it is, as it were, a daily incident of balloon- 
 ing. It is, therefore, the basis of the following obser- 
 vations : 
 
 The wind if the repetition may be excused does 
 not exist for the aeronaut, because he is enveloped in a 
 layer of air and is cut loose from the ground. All that 
 occurs, so far as the balloon is concerned, whether it 
 can be propelled or not, is the same that would occur if 
 the air were still. If the balloon can be propelled, it 
 can move in any direction in this atmosphere, which to 
 it is always calm, as if there were no wind. When mov- 
 ing forward, a breeze of greater or less force from front 
 to rear will be felt; this, however, has no connection 
 with the wind observed on the ground, but is a di- 
 rect effect of the movement of the propelled balloon 
 through the air. If the movement ceases, a complete 
 calm soon follows. 
 
 The balloon, which belongs to the layer of air 
 
42 AERIAL NAVIGATION. 
 
 through which it is moving, has nothing to fear from it, 
 whether it is capable of propulsion or direction or not. 
 The wind makes no difference either as to the sort of 
 force which is in operation during the movement or 
 as to the speed with reference to the surrounding air 
 ocean in which it lies. All that takes place in the air 
 ship takes place as if the air were motionless, and the 
 earth moves under it with a velocity corresponding to 
 that of the wind. 
 
 This idea being accepted, we can follow the effect of 
 the movement of the ground, which Commandant Re- 
 nard has clearly set forth by an illustration, in which it 
 is assumed that there are assembled an air ship and 
 twelve small air boats, which are floating over Paris ; 
 that they are for the moment without motion, and that, 
 furthermore, the wind is blowing from the west or, 
 which amounts to the same thing, the air is motionless, 
 and France with Paris is moving to the west with a 
 speed of about seven metres per second [fifteen miles 
 per hour]. 
 
 On an order from the ship the small boats leave the 
 point of assembly. They move out in twelve different 
 directions, the ship alone remaining in place. Assum- 
 ing the speed of these boats through the air to be about 
 three metres per second [six and a half miles per hour], 
 they will then at the end of an hour be at the circum- 
 ference of a circle which has a radius of six and a half 
 miles, with the ship at the centre. 
 
 The earth has, however, moved to the west during 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 43 
 
 this manoeuvre at the rate of fifteen miles per hour. 
 Paris, which an hour before lay directly under the sta- 
 tionary ship, has now disappeared and lies fifteen miles 
 away from it. On the other hand, the region fifteen 
 miles from Paris, with the Marne and the small town 
 of Chalons, stretches out under the plane of the circle 
 of twelve boats, and the circumference of this region 
 will be described by a circle of six and a half miles 
 radius, of which Chalons is the centre. The effect of 
 the west wind has thus been limited to the moving of 
 the air fleet fifteen miles to the eastward without in 
 any way changing the relative positions of the vessels. 
 All have moved together in the same direction. Their 
 respective movements with reference to the ground 
 have been as follows : 
 
 The geometric circumference of the positions 
 reached by the boats, propelled with the same velocity, 
 forms at a given moment a circle of which the radius 
 corresponds with the distance covered by their own 
 speed through the air and of which the centre has been 
 moved to a distance corresponding to the velocity of 
 the wind. 
 
 This supposition is illustrated in the following four 
 diagrams, wherein P is the point of departure of the 
 twelve boats. 
 
 P 1 is the point reached by the ship, being at the 
 same time the centre of the circle in which the twelve 
 boats are placed after an hour's travel. 
 
 B E is the position of one of the boats at any 
 
44 AfiRIAL NAVIGATION. 
 
 period of its travel. Its axis is parallel to the line 
 PM. 
 
 M is the point reached by the boat B E at the end 
 of an hour. 
 
 P P 1 is the distance representing the velocity, V, of 
 the wind in one hour. 
 
 Propeller 
 
 FIG. 3. 
 
 P 1 M is the distance travelled by the boat B E in 
 one hour, v. 
 
 P M is the distance representing the actual travel of 
 the boat in one hour as seen from the ground. 
 
 The sketch shows the propeller as placed at the for- 
 ward end of the boat. 
 
 The actual speed of the boat is therefore dependent 
 on the motive power, the form of the vessel, and its size 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 45 
 
 and weight. It agrees, approximately, with the rate of 
 propulsion of the balloon or air ship. 
 
 The application of these theoretical observations 
 shows three cases in which the speed of the air boat, 
 as measured from the ground, may be less, or equal to, 
 or greater than that of the wind. 
 
 If it is less than that of the wind, as is assumed in 
 Fig. 3, then the small circle in Fig. 4 shows the geo- 
 
 Fio. 4. 
 
 metric circumference reached by the boats after one 
 hour, and the large one that reached after two hours, 
 while P P 1 represents the velocity, Y, and P P 8 that of 
 2V. 
 
 Because V is greater than v, P is outside of the cir- 
 cle. If the two lines P T 1 and P T 2 are drawn tangent 
 to the large and small circles, then it is clear that the 
 boats originally starting from P cannot at the end of 
 one hour have passed beyond the small circle nor beyond 
 
46 AfiRIAL NAVIGATION. 
 
 the angle T 1 P T 2 . After two hours, for the same reason, 
 the whole series has moved to the circle whose centre is 
 P 2 , the velocity of the wind for the two hours being rep- 
 resented by 2 V, and that of the boats by 2 v. Neither 
 can the boats after two hours have gone outside of the 
 angle T 1 P T 2 . The whole atmospheric space may there- 
 fore be divided into two parts, one of which, included 
 within the angle T 1 P T 2 , can be reached by the boats, 
 and the remainder of the space, outside of it, cannot 
 be reached by them. The angle T 1 PT 2 will, for this 
 reason, be called the " attainable angle." 
 
 For the point M, reached after one hour, P 1 M is the 
 direction in the air, and P M the direction over the sur- 
 face of the earth, representing also the whole distance 
 travelled by the boat in one hour. The maximum value 
 of this distance is Pm or V-f v, and the minimum PM 1 
 or V v. In the first case the line of travel of the boat 
 and that of the wind coincide. In the second case these 
 lines are directly opposed to each other. 
 
 The maximum deviation occurs at the tangent lines 
 P M 1 and P M 2 , where the direction of the movement is 
 perpendicular to the actual line of travel. 
 
 The angle P 1 P M or P 1 P M 2 will be called the " angle 
 of the maximum deviation," and comprises one half of 
 the attainable angle. It is expressed by the formula 
 
 "V 
 
 Sin. a = y. If the inherent velocity of the boats is the 
 
 same as the velocity of the wind, then, according to 
 Fig. 5, both tangents PT 1 and PT 2 are in the same 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 47 
 
 line, and the angle of maximum deviation is a right 
 angle. The attainable angle then becomes equal to 
 two right angles, so that one half of the horizon is 
 accessible to the boats. Now, if P 1 M is the direction 
 of the boat or of its bow in the air, then PM is the ac- 
 tual line travelled over. The angle of deviation MPP 1 
 is equal to one half of the angle MPX formed by the 
 
 FIG. 5. 
 
 direction of the wind and that of the boat ; the maxi- 
 mum velocity is twice that of the wind or of the in- 
 herent velocity, and the minimum velocity is zero. 
 
 Finally, if the inherent velocity v is greater than 
 that of the wind V, then, according to Fig. 6, the point 
 of departure, P, will fall within the geometric circum- 
 
4-8 AfiRIAL NAVIGATION. 
 
 ference of the attainable positions, and the balloon can, 
 therefore, command the whole horizon. 
 
 In this figure PM and PM 1 show the actual travel 
 of the boats, and in the first case P M and in the second 
 PM * show the direction of their movement through the 
 air. The maximum velocity PM is again V v, and 
 the minimum velocity PM ! = v V, the inherent ve- 
 locity and that of the wind being in opposition. 
 
 M 
 
 FIG. 6. 
 
 This geometrical analysis sets aside many incorrect 
 observations, and demonstrates the falsity of the opinion 
 that the inherent velocity of the boat need not be greater 
 than that of the wind in order, when going against it, to 
 reach a desired point by tacking like an ordinary sailing 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 49 
 
 ship. This, indeed, is impossible, while, whatever the 
 direction of the boat or its bow may be, it can never 
 get beyond the attainable angle, and it is further to be 
 considered that in changing the direction it must fall 
 farther to the rear. Consequently, to make the progress 
 of the air ship possible, the condition is indispensable 
 that its inherent velocity should be greater than that of 
 the ordinary prevailing winds in those countries where 
 aerial navigation is to be attempted. 
 
 This condition is clearly of only relative impor- 
 tance. 
 
 The boat that conforms to the theoretical require- 
 ments in calm weather, according to Chapter IV, can be 
 controlled on certain days, and on certain days not, and 
 in proportion to its increase of speed is the ability to 
 control it extended. 
 
 In order to make this last condition practically use- 
 ful, we must study the periods during which the wind 
 blows with different velocities. To this end the velocity 
 of the wind has been regularly observed at Chalons by 
 means of a self -registering anemometer placed at the top 
 of a mast ninety feet high on the plain of Chatillon. 
 The results of these observations are given in the fol- 
 lowing table : 
 
50 
 
 AERIAL NAVIGATION. 
 
 VELOCITY OP THE 
 
 Number of days 
 
 
 WIND AT CHALAIS. 
 
 in 1,000 when the 
 
 
 
 velocity of the 
 
 
 In metres 
 
 In kilo- 
 
 wind at Chalais 
 may be expected 
 to be less than 
 
 Remarks. 
 
 per 
 second. 
 
 metres 
 per hour. 
 
 that given in the 
 first column. 
 
 
 2-50 
 
 9 
 
 109 
 
 According to the third column, 
 
 5-00 
 
 18 
 
 323 
 
 we may expect that the wind 
 
 7-50 
 
 27 
 
 543 
 
 will blow less than 40 metres 
 
 10-00 
 
 36 
 
 708 
 
 per second, or 144 kilometres 
 
 12-50 
 
 45 
 
 815 
 
 per hour, on every day of the 
 
 15-00 
 
 54 
 
 886 
 
 1,000. Nevertheless, greater 
 
 17-50 
 
 63 
 
 937 
 
 velocities have been observed 
 
 20-00 
 22-50 
 
 72 
 81 
 
 963 
 
 978 
 
 in exceptional cases. During 
 the 11,049 hours of observa- 
 
 25-00 
 
 90 
 
 986 
 
 tion there was once 162, twice 
 
 27-50 
 
 99 
 
 991 
 
 153, and nine times 144 kilo- 
 
 30-00 
 
 108 
 
 995 
 
 metres, during hurricanes 
 
 32-50 
 
 117 
 
 996 
 
 from the southwest, which 
 
 35-00 
 37-50 
 
 126 
 135 
 
 998 
 999 
 
 uprooted trees and destroyed 
 roofs. 
 
 40-00 
 
 144 
 
 1,000 
 
 
 42-50 
 
 153 
 
 1,000 
 
 
 45-00 
 
 162 
 
 1,000 
 
 
 According to this table, when the inherent speed is 
 12-50 metres per second [twenty-eight miles per hour] 
 the boat can move in any direction eight hundred and 
 fifteen out of one thousand days, and during seven 
 hundred and eight of these days it can make two me- 
 tres and a half per second [more than five miles and a 
 half per hour] against a wind with a velocity of ten 
 metres per second [twenty-two miles and a half per 
 hour] . 
 
 This velocity would make the free navigation of 
 the air practicable under most circumstances. "We may 
 therefore conclude that the aeronautic problem will be 
 
THE EXTRANEOUS OBSTACLE, OR THE WIND. 51 
 
 practically completely solved when we shall have ar- 
 ried at the production of a balloon that can be pro- 
 pelled with a velocity of twenty-eight miles per hour, 
 and when this velocity can be maintained, for example, 
 for a whole day, or for ten or twelve hours. 
 
 By renewals of the motive force at different relays, 
 which it is possible to maintain, like the taking of 
 water for locomotives, an even shorter period may suf- 
 fice. We need therefore grope in the dark no longer, 
 and this is a great point already gained. We may also 
 count on a constant improvement in the propelling ap- 
 pliances, and on the possibility of lessening the resist- 
 ance of the air as the flying machine runs through it, 
 which will guarantee the final solution of the question. 
 Many experimenters will unconsciously work together, 
 and the art of navigating the air will finally be due not 
 to a single person but to many. Attention must, how- 
 ever, first of all be given to more powerful motors with 
 the least possible weight. Even then everything will 
 not have been achieved, and serious difficulties may 
 yet remain; but we shall have secured the great con- 
 dition that dominates all others in aerial navigation. 
 
CHAPTER VI. 
 
 PRACTICAL RESULTS ALREADY REACHED IN MA- 
 CHINERY FOR PROPELLING BALLOONS. 
 
 BEFORE discussing the practical results thus far 
 reached with the machinery for propelling balloons, it 
 will perhaps not be amiss to observe that the note- 
 worthy experiments and observations undertaken on 
 the part of the Government at the military arsenal 
 at Chalais relate exclusively to balloons. These have 
 thus far applied to modified and elongated forms which 
 alone are used by the French military department. 
 The experiments instituted were undertaken under the 
 direction of Commandant Renard, from whose descrip- 
 tion of them this account is taken.* 
 
 Meanwhile, it will appear further that the study of 
 aerial navigation is also prosecuted in another direction, 
 and can even be regarded in some degree to have en- 
 tered a wider field of observation. This does not de- 
 prive the investigations at Chalais of great scientific 
 value and of much importance to the study of aero- 
 nautics. 
 
 * Revue de V Aeronautique Theorique et Pratique. Premiere 
 annee, 1888. 
 
PRACTICAL RESULTS ALREADY REACHED. 53 
 
 The aerostatic installation at Chalais (Meudon), 
 where the investigation of aerial navigation was car- 
 ried on with reference to its military use, had since 
 1878 been applied especially to the propelling of bal- 
 loons and to the applicability of electric motors. The 
 condition was assumed that the balloon must return to 
 its point of departure, which in the earlier experiments 
 was not fully accomplished. The inherent velocity of 
 the balloon had not been sufficient for this purpose, and 
 must, for that end, be increased. This involved a seri- 
 ous difficulty, inasmuch as the motive power per unit 
 of time is in general as the cube of the velocity, and 
 that this rule obtains in aerial navigation. It was 
 also further considered that for the success of the 
 experiment the former speed must be doubled, and 
 that, under nearly similar conditions, the weight 
 of the motive appliances must be reduced to one 
 eighth. 
 
 Account must further be taken of the former great 
 obstacle of the resistance of the air caused by the 
 spherical form of the balloon. It was therefore re- 
 solved to make this oblong, in order that its velocity 
 might be increased to the utmost. It was thus neces- 
 sary to satisfy two conditions, which it was apparently 
 impossible to reconcile that is, the weight of the ma- 
 chinery must be very much reduced in combination 
 with greatly elongated balloons, and this without im- 
 perilling their stability. Finally, other details, espe- 
 cially the position and satisfactory working of the rud- 
 
54 AERIAL NAVIGATION. 
 
 der, required improvements, to which little attention 
 had yet been paid. 
 
 The motive power employed in these experiments 
 consisted of an electro-dynamic apparatus with a gal- 
 vanic column admirably suited to it. The machinery 
 was of the usual Gramme type, and the greatest pos- 
 sible power was thus secured with the least weight. In 
 1885 this apparatus was replaced by a stronger combi- 
 nation supplied by Gramme. 
 
 "Both appliances together weighed about two hun- 
 dred and twenty pounds, and as the force developed at 
 the shaft was estimated at eight horse power, the weight 
 of the machinery was twenty-eight pounds per horse 
 power. 
 
 This result was certainly satisfactory. But the great 
 difficulty lay not so much in the weight of the machin- 
 ery as in that of the galvanic column required to pro- 
 duce a force of eight horse power during a certain time 
 fixed at two hours while the total weight must not 
 exceed eight hundred and eighty pounds ; correspond- 
 ing, therefore, with a weight per horse power, indepen- 
 dently of the working time, of Ill Ibs., 
 
 and per horse power, per hour, of 55 Ibs. 
 
 Previously, however, in 1883, a trial had been made 
 with an experimental model of a propelled balloon of 
 only sixty cubic metres' capacity and provided with a 
 motor of one half horse power, weighing twenty- two 
 pounds, and with a galvanic column capable of pro- 
 ducing one half horse power for one hour and a quar- 
 
PRACTICAL RESULTS ALREADY REACHED. 55 
 
 ter. The speed obtained with this model was very 
 satisfactory, reaching 4-5 metres per second. 
 
 Accordingly, the galvanic column for eight horse 
 power was made by Commandant Renard and the elec- 
 tro-magnetic motor by Captain Krebs. The advance 
 thereby made, as compared with accumulators, with 
 Tissandier's galvanic column, and with human power, 
 is shown in the following table : 
 
 
 Renard's gal- 
 vanic column. 
 
 Accumulators 
 (practical aver- 
 age of the best 
 appliances). 
 
 Tissandier'a gal- 
 vanic column. 
 
 Man power 
 (eight men em- 
 ployed by 
 Dupuy de Lome). 
 
 Total weight* 
 
 400 
 
 
 225 
 
 600 
 
 Maximum energy in horse 
 power of 75 kilogrammes 
 on the shaft . . 
 
 9 
 
 
 1-33 
 
 0-65 
 
 Time of working 
 
 1 h. 45 m. 
 
 4h. 
 
 2h.30m. 
 
 3 h. 
 
 Weight per horse power, 
 independently of time : 
 Actual weight 
 
 44-4 
 
 300 
 
 170 
 
 900 
 
 Weight, Renard's column 
 being taken as the unit. 
 Weight per horse power 
 per hour : 
 Actual weight . 
 
 1-0 
 25-0 
 
 6-7 
 75 
 
 3-8 
 68 
 
 20-3 
 300 
 
 Weight, Renard's column 
 being taken as the unit. 
 
 1-0 
 
 3-0 
 
 2-7 
 
 12-0 
 
 If the motive power alone is considered without ref- 
 erence to its duration, then the weight of the galvanic 
 column of Chalais is only one fourth of that of Tis- 
 sandier, one seventh of that of accumulators, and one 
 
 * The weights given are in kilogrammes. 
 
56 AERIAL NAVIGATION. 
 
 twentieth of that of human power, according to Dupuy 
 de L6me. 
 
 If, on the other hand, account is taken of the dura- 
 tion of the working, and if the weight is reduced to the 
 unit of one horse power per hour, then the table shows 
 that the galvanic column of Chalais is three times 
 lighter than the accumulators and the galvanic column 
 of Tissandier, and twelve times lighter than human 
 power, as obtained by Dupuy de Lome. 
 
 The improved application of electric power in the 
 case of the balloon " La France " has thus marked a 
 great advance, and I would recall in this connection 
 (Chapter IV) the fact that Giffard, in 1855, in order to 
 lessen the resistance of the air, risked an ascent in a 
 balloon ten metres in diameter and seventy metres long. 
 The proportion was one to seven, and the result was 
 that the heavy pitching during the descent soon 
 wrecked it. 
 
 The balloons of Dupuy de Lome and Tissandier, 
 whose stability left nothing to be desired, were not 
 nearly so long as that of Giffard. The resistance to 
 the air was, however, with reference to the weight re- 
 quired for the motive power naturally much greater. 
 
 For this reason the elongation adopted at Chalais 
 in 1884 was sufficiently reduced. The balloon " La 
 France " had a diameter of 8 -4 metres and a length of 
 50*4 metres, so that the proportion was one to six. 
 Nevertheless, various improvements were made and pre- 
 cautions taken which obviated the danger of pitching. 
 
PRACTICAL RESULTS ALREADY REACHED. 57 
 
 A comparison of the results obtained with the above- 
 named balloons seems important with regard to the 
 elongation of the form. These are set forth in the 
 following table, wherein the value of the propelling 
 force is also shown per unit of cross-section of the 
 resisting surface, and where it is to be observed that 
 the fastest balloon is that which, other things being 
 equal, has the greatest power per unit of resisting 
 surface : 
 
 
 ll 
 
 Duptiy de 
 Lome (1872). 
 
 G. Tissandier 
 
 (1883). 
 
 Ilji 
 
 Dimensions of the balloon: 
 Diameter in metres 
 
 10-0 
 
 14-84 
 
 9-20 
 
 8-40 
 
 Length in metres 
 
 70-0 
 
 36-12 
 
 28-0 
 
 50*40 
 
 Relation of the diameters to 
 
 7-0 
 
 2-43 
 
 3-04 
 
 6*0 
 
 Total propelling force in 
 horse power. 
 
 3-0 
 
 0-65 
 
 1*33 
 
 9*0 
 
 Area of cross - section in 
 square metres 
 Propelling force per 100 
 square metres cross-sec- 
 tion: 
 In horse power 
 
 78-5 
 3-83 
 
 172-8 
 0-38 
 
 66-5 
 2-0 
 
 55-4 
 16*25 
 
 Compared with that of the 
 balloons of Dupuy de 
 Lome 
 
 10-0 
 
 1-0 
 
 5-3 
 
 42'7 
 
 Compared with that of the 
 balloons of G. Tissandier 
 
 1-9 
 
 0-19 
 
 1-0 
 
 8-1 
 
 The power per unit of cross-section thus appears to 
 have increased materially, for with Giffard's balloon it 
 was ten times, with Tissandier's five times, and with that 
 of Chalais forty-two times the power of Dupuy de L6me's 
 
58 AERIAL NAVIGATION. 
 
 balloon. The Chalais balloon has also eight times the 
 power of Tissandier's. 
 
 From the foregoing general rule concerning the re- 
 lation between power and speed, and from the figures 
 given above, it is further to be considered that the speed 
 of the Chalais balloon must amount to twice that of 
 Tissandier a relation which was very closely established 
 by experiment. 
 
 In conclusion, it appears, from a comparison of " La 
 France " with Tissandier's balloon, that the weight of 
 the motive power employed is in the proportion of one 
 to four; that the elongation of the former was twice 
 that of the latter ; and that the stability, because of the 
 precautions taken, was not endangered ; and, finally, that 
 the power per unit of resisting surface, or cross-section, 
 amounted in the former to eight times that of the latter. 
 
 Furthermore, the Chalais balloon differed in having 
 various improvements relating to the general form of 
 the envelope, the arrangement of the car and of the 
 rudder, the placing of the rudder and of the propellers, 
 etc. These details all contribute in greater or less de- 
 gree to the improvement of the conditions contributing 
 to speed and to steadiness of direction, which had in its 
 predecessors left so much to be desired. In a word, a 
 balloon had been made constituting a rigid mass in the 
 air, and within the limits of its movement obeying 
 immediately the least indication of its rudder. 
 
CHAPTEE VII. 
 
 THE YEARS 1884 AND 1885. 
 
 THE experiments with this balloon in 1884 and 1885 
 produced results which are of great use in the study of 
 aerial navigation. The first trial was made in calm 
 weather on August 9, 1884. The two aeronauts were 
 Commandant Reuard and Captain Krebs. They thought 
 it advisable to limit the trial to a few kilometres, and not 
 to make use of the full indicated power, which, however, 
 did not prevent their expectations being exceeded by 
 their success. As soon as they had reached the wooded 
 heights that enclosed the valley of Chalons the pro- 
 peller was put in motion. The balloon was immedi- 
 ately started forward and yielded readily to the indica- 
 tions of the rudder. Renard testified that they were in 
 complete control of the direction, and that they could 
 turn the balloon towards any point as easily as they could 
 a steamer in a smooth sea. 
 
 After having reached Villa Comblay, the bow was 
 headed for the meadow from which the balloon had 
 ascended, it having been decided to alight there in 
 
60 AfiRIAL NAVIGATION. 
 
 spite of the surrounding obstacles.* They reached this 
 field at an elevation of three hundred metres. The 
 speed of the screw was then slowly reduced, and the 
 safety-valve was opened, so that a slow descent fol- 
 iowed. With the help of the motor and with the rud- 
 der they kept the balloon almost immediately over the 
 landing place and laid the car gently on to the grass. 
 
 In this trip the important conditions were fulfilled 
 that the balloon had been controlled with practical 
 exactness, that it had moved freely in the air, and that 
 it was brought back exactly to the point of departure. 
 
 Three more experiments were made in 1884. On 
 September 12th the balloon went up in a fresh breeze 
 blowing from the west with a velocity of about six 
 metres per second (about thirteen miles per hour). It 
 withstood the wind, and might probably have been 
 brought back to Chalais if some mishap had not dis- 
 abled the machinery. 
 
 The accident was of very little importance in itself, 
 but it made an unfavorable impression and had a bad 
 effect. It probably contributed to this that many were 
 entirely opposed to experimenting exclusively with bal- 
 loons. This was, however, a wrong opinion, and was 
 due to a misconception of the scientific purpose in 
 view. 
 
 * The field is about seventy-five metres wide by one hundred 
 and fifty metres long, and is surrounded by high trees and build- 
 ings, while it is bordered at one side by a pond of some seven 
 acres. 
 
EXPERIMENTS WITH BALLOON "LA FRANCE." 61 
 
 Afterwards, on the 8th of November, another as- 
 cent was made, and the precaution was taken to carry 
 along the whole galvanic column. The weather was 
 beautiful, and the balloon was directed towards Bou- 
 logne. 
 
 After the Seine had been crossed near the bridge at 
 Billancourt, it was, as on the first trial, made to return 
 to Chalais without the least difficulty. During this 
 trip it attained a speed of six metres per second (thir- 
 teen miles per hour). In the afternoon of the same 
 day it was sent up again. In consequence of the rising 
 of a fog they did not dare to venture far from Chalais. 
 The balloon remained soaring within the circumference 
 of the park, and the landing was made in the field 
 from which it started. These ascents were always made 
 by the same aeronauts Messrs. Renard and Krebs 
 whose attention was given exclusively to the propelling 
 of the balloon, so that there was no question of a cor- 
 rect record of speed. They confined themselves to the 
 counting of the revolutions of the screw, and to the 
 measuring of the force and tension of the currents re- 
 sulting from the source of power. From these figures, 
 however, the actual speed has since been worked out in 
 close comparison with those of 1885. 
 
 These first experiments showed the need of a third 
 man in the balloon, in order that the necessary meas- 
 ures for steering could be carried out with greater 
 security. This required that the weight of the balloon 
 should be reduced, and consequently that its different 
 
62 AERIAL NAVIGATION. 
 
 parts should be modified. The car was furnished with 
 a light and sufficiently strong motive apparatus by 
 Gramme, which had for many weeks been most severely 
 tested. 
 
 On the 25th of August, 1885, the trials were re- 
 sumed. In the first flight, the return to Chalais was 
 prevented by the velocity of the wind. Save for this 
 apparent misfortune, the day's experiment was very 
 useful, as it indicated the satisfactory working of the 
 machinery. 
 
 On the 22 d of September, in a northwest wind 
 blowing four metres per second (nine miles per hour), 
 the balloon went up from the usual spot, with Com- 
 mandant Eenard and Mr. Dute Poitevin, the civil 
 aeronaut of the arsenal at Chalais. It was headed 
 towards Paris and started straight against the wind. 
 The full force of the machinery was employed, and, 
 notwithstanding the head wind, the balloon soon passed 
 the Seine, and shortly after that reached Boulogne and 
 Point-du-Jour. After passing the fortifications, the 
 course was laid towards Chalais, and, now favoured by 
 the wind, the balloon arrived there promptly. Eleven 
 minutes sufficed for the return trip, while the outward 
 trip had occupied forty-seven minutes. The trial was 
 repeated the next day, and though the wind now car- 
 ried the balloon towards Paris, the expedition was nev- 
 ertheless completed under the same conditions as the 
 day before 
 
 After that, the experiments were discontinued, as it 
 
EXPERIMENTS WITH BALLOON "LA FRANCE." 63 
 
 was desired to make various improvements and to in- 
 crease the power and speed of the machinery. 
 
 Concluding now the consideration of air balloons, 
 we will next turn our attention to an examination based 
 on Nature and on the movement of birds. 
 
CHAPTER VIII. 
 
 THE FLIGHT OF BIRDS. 
 
 THE movements of a bird in flying are generally too 
 complicated and too rapid to be observed in the usual 
 manner and with the naked eye. Furthermore, the 
 laws which govern the resistance of the air were until 
 now so imperfectly understood,* that it was not pos- 
 sible to take full account of the two important facts : 
 that the bird, supported only by the exertion of its own 
 mechanical force, is able to maintain its position in the 
 air ; and that flight is possible only because this fur- 
 nishes a fulcrum for the wings. Now, however, as the 
 study of mechanical flight has been taken up in such a 
 
 * The study of the laws governing the resistance of the air 
 has always been carried on under the simplest conditions. We 
 have confined ourselves to the resistance that rigid surfaces of 
 certain forms offer when they remain in the same relation to the 
 line of motion. These observations are, however, not applicable 
 to bird flight, because the resisting surfaces of the bird are very 
 complex. Their form and size, under the influence of the resist- 
 ing medium, and according to the greater or less spread of the 
 wings, are constantly being modified ; and, finally, these surfaces 
 are in constant motion and in constantly changing relation to the 
 line of advance. 
 
THE FLIGHT OF BIRDS. 65 
 
 systematic manner, an understanding of the flight of 
 birds has become more and more necessary; and we 
 borrow the following observations from the valuable 
 work, Le Vol des Oiseaux^ of Prof. E. J. Marey, of 
 Paris.* 
 
 The former opinion that man can fly for the simple 
 reason that birds fly now finds no acceptance. It had, 
 indeed, no reasonable foundation, because the most 
 complete means of conveyance attained up to this time 
 are not borrowed from Nature, but differ widely from 
 it. A correct knowledge of the laws of Nature should 
 be all the more valued, however, because through the 
 development of science in many directions it will be- 
 come more and more possible to establish the physio- 
 logical and mechanical conditions of bird flight. We 
 can already make observations as to all the movements 
 made in the raising and depressing of the wings, and 
 can count them, and can measure the strength of the 
 birds. We can also determine their course with much 
 exactness, and, from the manner of their flight, can 
 even determine their successive retarded and acceler- 
 ated movements. 
 
 In order to get a correct idea of the mechanism of 
 bird flight, it will, however, be necessary also to pay at- 
 tention to the anatomical similarity of the organs of 
 motion observed in birds and in animals moving on the 
 
 * Le Vol des Oiseaux, by E. J. Marey, Member of the Insti- 
 tute and of the Academy of Medecine ; Professor at the College 
 of France, Paris. G. Masson, 1890. 
 
66 AERIAL NAVIGATION. 
 
 earth's surface or in the water. Even anatomy cannot 
 be disregarded, for flying is not made impossible by 
 clipping the wings, nor by depriving them of some of 
 the flight feathers ; neither is the tail absolutely neces- 
 sary as a rudder, for in its absence the bird finds other 
 means which serve the purpose. Therefore, due con- 
 sideration must be given to anatomy. 
 
 Observations as to the movements of birds in flying 
 have been made possible by the graphical methods of 
 chronometric observation and photography, by optical 
 analysis of the movements, and by instantaneous pho- 
 tography. By these means we have in a measure ana- 
 lyzed the movements of birds ; yet, in order to obtain 
 practical results therefrom, we must be able to imitate 
 their flight, and attempts have been made in this direc- 
 tion. We are already able to reproduce some of their 
 movements, such as the up and down strokes of the 
 wings, and the floating in the air of a winged machine, 
 in which the weight and the surface provided for its 
 support are brought into accord, while w r e have been 
 able to determine the various directions taken by differ- 
 ent forms of such machines in their flight. 
 
 These imitations have already furnished encour- 
 aging results, so that the artificial appliances imi- 
 tating the action of bird flight have been observed 
 by optical instruments or by chronometric photogra- 
 phy to detect imperfections which were invisible to 
 the eye. 
 
 It is to be remembered in this connection that when- 
 
THE FLIGHT OF BIRDS. "67 
 
 ever a mechanical problem is thoroughly studied, the 
 mathematical formulae for its application can be estab- 
 lished, as has been done for nearly all machines. We 
 have, however, not yet gone so far as this with reference 
 to flying, and we have until now tried in vain to form a 
 scientific theory concerning it. For this reason the cal- 
 culations thus far made are little to be relied upon, and 
 considerable time will probably elapse before most of 
 the questions relating to it will be cleared up by experi- 
 ment and observation. Furthermore, while there is no 
 doubt that we shall eventually understand all the move- 
 ments of birds, there will still be needed for their appli- 
 cation a complete knowledge of the resistance that the 
 wings encounter in the air. This investigation is hardly 
 begun. We are, therefore, still far from attaining the 
 end in view, but we do know in what direction to turn 
 our efforts, and we are in a position to take due account 
 of the requirements already determined or still to be 
 learned. 
 
 The movements of all birds in flying are very differ- 
 ent, and they depend on various circumstances. They 
 are, for example, different in regular flying, in soaring, 
 and in sailing in the air the last two forms of fly- 
 ing being made with almost motionless, outstretched 
 wings. 
 
 We shall endeavour to set forth these methods of 
 flight after having made some observations on the phe- 
 nomena connected with the flying of the common boy's 
 kite, which has already been brought into the realm of 
 
68* AERIAL NAVIGATION. 
 
 science by that renowned student of Nature, Franklin, 
 who used it to prove the existence of electricity in 
 the air.* 
 
 * For this purpose a thin copper wire was substituted for 
 the string. 
 
CHAPTER IX. 
 
 THE BOY'S KITE. 
 
 THE laws that come into play in the flying of a kite 
 are involved in the flight of birds without the actual 
 movement of the wings, such as the sailing and soaring 
 above referred to. The kite is flown under two very 
 different conditions, namely, in a wind of greater or 
 less force, and in calm weather, or when the air seems 
 to be in a state of rest. 
 
 In the first case it is sufficient that the string of the 
 kite be held firmly or tied to a fixed -point, because if 
 ballasted by its tail it rises of its own motion, and con- 
 tinues to rise until it reaches an elevation where it 
 stands still in the air, and remains there so long as the 
 wind maintains the same velocity. In the second case, 
 it will rise in like manner whenever it is moved forward 
 by a person running and drawing the string with him. 
 This movement has only the result of creating a wind 
 under the kite, although it is not the air, but the kite, 
 that moves. The result of both forms of motion is the 
 same. (See Chapter V.) 
 
 Let it now be supposed that in both cases the kite is 
 
70 AfiRIAL NAVIGATION. 
 
 maintained steadily at the same height, and that it has 
 as little tendency to rise higher as to fall, so that the re- 
 sultant of the air pressure resolves itself into a vertical 
 and a horizontal force. 
 
 The vertical force is, in this analysis, applied to 
 overcome gravitation, and must, therefore, in order to 
 maintain the stability and equilibrium of the kite, be 
 equivalent to its weight. 
 
 The horizontal force perceptibly indicated by the 
 tension of the string will, however, be neutralized, for 
 the immovable position of the kite shows that the equi- 
 librium attained is not disturbed by any of the existing 
 forces. 
 
 Still, until this condition of equilibrium is attained 
 that is, so long as the kite is rising it is exposed to vary- 
 ing air pressures, and these are dependent on the angle 
 at which its surface is presented to the wind. At the 
 moment when the kite is first let up, we may assume 
 that its face is nearly perpendicular to the current, and 
 that the whole force of the wind acts horizontally 
 against it. The kite then develops a maximum draw- 
 ing power, and the string is under the strongest tension, 
 so that the vertical force is barely sufficient for the lift- 
 ing of the weight. 
 
 In rising, however, the angle of the kite with the 
 direction of the wind becomes constantly smaller, and 
 so the tension on the string grows less. We feel, as it 
 were, less pulling by the kite, and the decrease continues 
 
THE BOY'S KITE. 71 
 
 until the moment when it reaches its greatest height 
 and stands still, or the moment when it arrives at its 
 state of equilibrium. 
 
 The equilibrium is disturbed, however, whenever the 
 wind rises or becomes stronger, or whenever the person 
 holding the string moves forward. The kite will by 
 this increase of wind tend to rise higher ; it will, on the 
 other hand, tend to fall when the velocity of the wind 
 decreases. 
 
 Furthermore, the force exerted on the kite may have 
 different values with winds of the same force. This is 
 dependent on the manner in which the string is attached 
 to it, because this determines the angle at which the sur- 
 face is presented to the wind. 
 
 The rising of the kite, then, depends on both the 
 velocity and the direction of the wind and on the angle 
 of the kite with this direction ; for it is by this that the 
 development and effect of the horizontal and vertical 
 forces which act to raise the kite, and which there- 
 fore present themselves under modified forms, are regu- 
 lated. 
 
 Let it be supposed that the place of the kite is taken 
 by a bird with outstretched wings moving with great 
 velocity through a still air, or that it stands motionless 
 in a strong wind, with a tendency to fall towards the 
 earth ; then, in both cases, the wings are exposed to the 
 action of the wind, and the composite air pressure on 
 the bird's mass will act in the same manner as on the 
 
72 AfiRIAL NAVIGATION. 
 
 kite. This can thus be divided into two forces, of which 
 the vertical is equal to the gravity or the weight of the 
 bird ; and the other the horizontal, whether due to the 
 velocity of movement or to the resistance offered to the 
 wind by the body and wings, equals the pressure against 
 these. 
 
CHAPTER X. 
 
 THE ORDINARY FLYING OF BIRDS "ROWING" 
 FLIGHT. 
 
 THE rowing flight of birds takes its name* from 
 the similar movement in the water of oars .moved by 
 rowers. The two movements have, however, the differ- 
 ence that that of the oars is horizontal, while that of the 
 wings is vertical. The work of propelling a rowboat is 
 developed during the forward stroke of the oars in the 
 water, while little if any force is developed during the 
 return stroke, because this movement is in the air. 
 
 The mechanical force required for " rowing " flight 
 is developed during the downward stroke of the wings, 
 not while they are being lifted. A part of the force is 
 taken up and accumulated in the mass of the bird, as 
 momentum, which during the passive phase, or while 
 the wings are being lifted, serves to support the body 
 of the bird against the air, like a kite. 
 
 The amount of force so developed is not a constant 
 quantity. It tends towards a minimum, and this is 
 
 * Ordinary flying, with regular strokes of the wings, is called, 
 in Dutch, Roeiende flight. The designation "rowing" is used 
 in all cases as its English equivalent. 
 
74 AERIAL NAVIGATION. 
 
 reached when the number and extent of the strokes are 
 reduced to the utmost. This indeed is fully shown by 
 various experiments (see Chapter VIII), by which sev- 
 eral problems connected with animal motion may be 
 solved. 
 
 When mechanical flight is under consideration the 
 question, What force does the bird consume in flying? 
 acquires the greatest interest. On this will indeed de- 
 pend the power to be applied to the propelling of flying 
 machines, whether the muscular strength of the man 
 can be used, or whether special mechanical appliances 
 must be provided. 
 
 To determine this, the sum of the energy expended 
 being the force multiplied by the distance travelled 
 by its point of support must be determined. This we 
 express in the case of living or animal motive power, as 
 in the case of ordinary motors, in kilogramme-metres.* 
 
 It is to be remembered here that it is very difficult 
 to estimate with precision, in the case of the flight of 
 a bird, the force and the distance through which the 
 supporting point travels, because of the complication 
 and rapidity of the movements. Observations and ex- 
 periments concerning bird flight have, therefore, pro- 
 duced no satisfactory results from which to estimate 
 the energy consumed in its rowing flight, f This point 
 
 * This unit indicates the power required to raise one kilo- 
 gramme to the height of one metre (the unit in English is " foot- 
 pounds "). 
 
 f In this connection, the strange calculations of Navier may 
 
THE ORDINARY FLYING OF BIRDS. 75 
 
 must some day be reached by the help of chronometric 
 photography, but these observations are of the most 
 delicate character, and their application calls for much 
 scientific knowledge. It is to be remembered also that 
 they relate only to the condition of the moment, and 
 that they are made while the force exerted by the bird 
 is changing every instant, and this decreases as its speed 
 increases. In rowing flight the force exerted reaches 
 its maximum, though only for a few moments, at the 
 instant when the bird starts up ; as soon as a certain 
 speed is reached the flight becomes easier, and the air 
 gives greater support to the wings, while the length 
 and number of strokes diminish. Consequently, the 
 bird needs to exert considerably less force in full flight 
 than in its rising or in the beginning of its flight. 
 
 be recalled, by which it is shown that thirteen swallows exert one 
 horse power, or 75 kilogramme-metres, per second. The above 
 uncomplimentary expression is justified because the data on which 
 the computation was founded were not reliable. Without taking 
 account of the nature of the movements of bird flight, or of the 
 resistance of the air, Babinet thought it might be assumed that, 
 considering that a bird would, in consequence of gravitation, fall 
 4-90 metres in the first second, in order to fly horizontally it must 
 exert as much force as would be necessary to lift its own weight 
 4-90 metres. Concerning this, it is pertinent to say that if we 
 take the unit of time not as one but as two seconds, the height of 
 fall becomes 4*90 metres x 2 s , or 19'60 metres, and that it must, 
 therefore, lift its weight 19'60 metres in two seconds, or 9 - 8 metres 
 per second, and so must exert twice the force. D'Esterno has, 
 therefore, thought it necessary to consider only the height of fall 
 during the time in which the bird, before flying, is subjected to 
 the influence of accelerating gravitation. Now, this is a correct 
 standard, but it can be established only by many experiments. 
 
76 AERIAL NAVIGATION. 
 
 It has, in fact, been observed that in the case of the 
 sea-gull the number of strokes per second in full flight 
 is little more than three, while it is as much as five at 
 the beginning of the flight.* 
 
 Let us now suppose that each stroke of the wings 
 requires the same force, then the amount of work done 
 at the beginning of the flight and in full flight will be 
 in the proportion of five to three. 
 
 Furthermore, the extent of the strokes decreases 
 with their number, and amounts in full flight to only 
 about one third part of that made at the first moment 
 of rising. It may thus be estimated that if, at the be- 
 ginning of the flight, T represents the work done by 
 the bird in one second, the work in full flight will 
 amount to only -f X i T = % T, and so that the more 
 
 * It is established that the average number of wing-strokes per 
 second is, for the 
 
 Stork If stroke. 
 
 Carolinian kite 3 strokes. 
 
 American vulture 2f " 
 
 Great gull 3 " 
 
 Common gull 5-J " 
 
 Pelican 1^, or 70 to the minute. 
 
 Pigeon 10 strokes. 
 
 The wing-strokes are, moreover, governed by various conditions. 
 In descending, they decrease, and sometimes cease entirely, when 
 the flight is very rapid. They increase, on the other hand, in ris- 
 ing and when the bird holds itself in one position, when it desires 
 to increase its speed, when it carries a heavy body with it, and, 
 finally, when its wings are clipped. 
 
 This has already been observed by Mouillard in the case of 
 pigeons whose flight feathers he had cut to make the wings 
 shorter. 
 
THE ORDINARY FLYING OF BIRDS. 77 
 
 and more rapid the movement, the less and less effort 
 will be required to maintain the bird's position in 
 the air. 
 
 It is also to be observed in this connection that the 
 movement of the wings meets with more supporting re- 
 sistance in the air as the horizontal speed of the bird 
 increases. This appears clearly in the flight of a gull 
 over the surface of the sea. It makes at first long 
 strokes of at least one hundred or one hundred and ten 
 degrees scope, but as its speed increases the sweep of 
 the stroke decreases, until the angle covered is only 
 thirty to forty degrees. These birds sometimes fly for 
 a considerable space close to the water without rising 
 or falling. Their movements are then marked by great 
 regularity. 
 
 Further, it appears that the elevation at which the 
 bird flies is maintained when the sweep of the strokes 
 lessens, and that those of less sweep suffice for its sup- 
 port then, just as the greater sweep did at the begin- 
 ning of the flight. The difference shown between the 
 beginning and the continuance of horizontal flight de- 
 pends on this, that as an increased speed is attained a 
 firmer support is given by the air. 
 
 This supposition is confirmed by the following ex- 
 periment : The legs of a large gull were tied to a long 
 string that could unwind readily. At first the bird 
 flew off as though it were free, but as soon as further 
 horizontal movement was prevented by a tension on the 
 string it fell heavily down, and was, in spite of the 
 
78 AERIAL NAVIGATION. 
 
 movement of the wings, unable to support itself in the 
 air. This phenomenon is, in certain respects, the op- 
 posite to that which we notice when the bird begins to 
 fly, because there is then an increasing velocity. 
 
 The fact last stated seems to be explained by the re- 
 sistance of the air : that is, when a rapid movement is 
 given to the air by an external force, as by the down- 
 ward stroke of the wings, its resistance becomes less. 
 Thus, when the bird moves its wings up and down 
 without changing its position, they act on a column of 
 air which at first offers resistance, but afterwards, by 
 reason of its quickened motion, escapes from under the 
 wings. On the other hand, if the bird is moving hori- 
 zontally, then the wings bear successively on a series of 
 columns of air, and they find in each of these the origi- 
 nal resistance due to its inertia. This theory has been 
 established by a series of experiments. 
 
 While the vertical resistance of the air is thus in- 
 creased by a swift movement of the bird, the same is 
 not true with reference to horizontal resistance. This 
 decreases, however, during a certain time, under the 
 influence of the velocity, which is shown by the lifting 
 wing, which presents itself in the air at an angle of in- 
 creasing acuteness, but when that angle has decreased 
 to a minimum the resistance of the air to the move- 
 ment of the bird no longer decreases it increases, on 
 the contrary, as the squares of the velocities. Thus the 
 velocity of flight has its limits. 
 
 We may, indeed, in the case of all birds, observe 
 
THE ORDINARY FLYING OF BIRDS. 79 
 
 that the flight at its beginning requires the exertion of 
 much force. Pigeons, which can for such a consider- 
 able time support themselves easily, almost playfully, 
 high in the thin air, and which can fly to such great 
 distances, will after successive ascents with a flight of 
 hardly twenty metres' length, refuse to fly at all, gasp- 
 ing with open beak. If they are then compelled to fly 
 again, they take only a downward sweep, and go almost 
 immediately to rest. 
 
CHAPTER XI. 
 
 HOVERING FLIGHT. 
 
 HOVERING flight is to be regarded as the gliding of 
 the bird over a stratum of air. It occurs only in a calm, 
 and requires further, as a condition for this movement, 
 that the bird shall previously acquire a rapid motion. 
 This speed, however it may first have been acquired, will 
 be slowly expended and used up during the hovering^ 
 It serves to support the bird and to overcome gravita- 
 tion. Thus, in like manner, in the falling sweep gravi- 
 tation tends to increase the speed, so much so that it 
 may be fully maintained during the whole time of such 
 descending flight. Hovering flight has recently been 
 compared with the flying of a kite, and has been ob- 
 served under the following circumstances : 
 
 1. The bird which has for some time flown with 
 strokes of the wings discontinues the strokes for a time, 
 and assumes the horizontal movement ; or 
 
 2. It lets itself fall from a high position and spreads 
 its wings as it gains sufficient speed for hovering. The 
 force developed in falling carries the bird along, after the 
 manner of a kite of which the string is drawn forward. 
 Such hovering, which interrupts the regular rhythm of 
 
HOVERING FLIGHT. 81 
 
 rowing flight, may often be noticed in the case of herons, 
 storks, hawks, gulls, vultures, and in general with all 
 birds with outstretched wings. 
 
 In this flight the bird cannot raise itself in the air 
 without greater or less loss of the velocity which has 
 been attained by the movement of the wings. The loss 
 of elevation, theoretically assumed, is not always percep- 
 tible to the eye, neither is it always inevitable. It ap- 
 pears, in fact, by observation that the bird cannot only 
 hover without falling, but in case of need it can with 
 the loss of a good part of its velocity rise higher. In 
 this connection it is interesting to watch the manner of 
 flight of falcons. They begin when set free by flying 
 against the wind at an angle with the horizon of from 
 fifteen to twenty degrees, which apparently calls for 
 much effort ; for if the distance to be gone over is too 
 great, the bird interrupts its rising flight from time to 
 time and is carried back horizontally by the wind so far 
 as to come each time over the point from which it 
 started. It thus rises by a zigzag course without a loss 
 of elevation in the return movement, and continues thus 
 until it has reached the position required for falling 
 upon its prey. Its fall from the high air is made with 
 great velocity, the wings being pressed closely against 
 the body, describing a curve which brings it directly 
 upon the quarry. Should this, however, escape it, then 
 a slight change in the position of the wings and of the 
 body suffices to turn its course upward again and to 
 carry it back to the height from which it first swooped 
 
82 AERIAL NAVIGATION. 
 
 down. This manoeuvre is sometimes made repeatedly, 
 until the falcon reaches its quarry and brings it tumbling 
 to the earth, where it is despatched. 
 
 The pursued bird, on the other hand, tries to escape 
 by turning suddenly upward or to one side, but the 
 direction of the swoop of the falcon is nearly always so 
 precise that it rarely misses its aim. 
 
 The velocity of its descent is greater in proportion as 
 its direction is steeper. The falcon sometimes comes 
 down perpendicularly and, as it were, in the twinkling 
 of an eye. The duration of this fall is estimated to be 
 in this case only the one-hundredth part of that of the 
 ascent. The rising from such a descent is, however, 
 very rapid. 
 
 The hovering flight which a bird can assume when 
 it descends from an elevation may 'also sometimes be 
 used to rise to a certain height. 
 
 When a pigeon seated at the edge of a roof flies to 
 the ground, it does this with a hovering movement, but 
 in various ways, according to the point to be reached, 
 whether this is vertically under the point of departure 
 or at some distance from it horizontally. In the first 
 case the pigeon may simply go straight down by spread- 
 ing the wings and the tail in such a way as to have three 
 points of support in the air. The velocity attained 
 is nevertheless considerable, and before it reaches the 
 ground it has to check its motion with several strong 
 strokes of the wings. In order to reach the ground with 
 less velocity, the pigeon sometimes describes circles 
 
HOVERING FLIGHT. 83 
 
 which are wider according as a slower descent is re- 
 quired. On the other hand, if the point to be reached 
 is horizontally far enough away from the starting point 
 to be reached by a sloping sweep, the bird simply lets 
 itself go, gliding downward through the air with out- 
 stretched wings, and if the movement given by gravita- 
 tion is insufficient, it is aided by a few strokes of the 
 wings. This brings up an important question, What is 
 the greatest horizontal distance that a bird can cover 
 when it lets itself glide through the air from a given 
 height? This is dependent in downward hovering on 
 the relation of the height of the drop to the horizontal 
 distance traversed. This relation has been variously 
 estimated. According to D'Esterno, it must be taken as 
 one to eight, equal to an angle of seven degrees formed 
 between the line traversed and the horizon. According 
 to Moulliard, the angle amounts to ten degrees. Tatin 
 found by his experiments with hovering appliances that 
 the proportion of one metre vertical to eight metres 
 horizontal gave the slightest slope that could be de- 
 pended upon. 
 
 Finally, Bretonniere, on the basis of his observations 
 on the flight of storks, concludes that the least slope at 
 which hovering can take place is at an angle with the 
 horizon of ten degrees.* This rough estimate or calcu- 
 
 * Bretonniere's observations related to the descent of storks 
 from the high-lying rocks on which stands the city of Constantino. 
 According to these, the birds swept through the air to a distance 
 in a direct line of more than one kilometre. The velocity of the 
 
84: AERIAL NAVIGATION. 
 
 lation is based on very close measurements of the relative 
 heights and distances between the places of departure 
 and of arrival of the birds. In estimating the angle be- 
 tween the line of flight and the horizon, it is to be con- 
 sidered that the course is never a right line for its whole 
 length, but is at the beginning a curved line, which ap- 
 pears to be parabolic, and at the start nearly vertical, 
 slowly attaining the minimum slope, which is continued 
 to the end. An imaginary line was drawn through the 
 points of departure and arrival, and this was taken as the 
 average inclination of the course. 
 
 Here the question arises whether or not the bird al- 
 ways takes such account of the effect of gravitation as to 
 reduce the resistance of the air to its horizontal progress 
 to a minimum, so as to reach the end of its course just 
 when its momentum is expended. This condition being 
 complied with, hovering at an angle of ten degrees may 
 be observed to take the best advantage of gravitation for 
 traversing a given horizontal distance. Knowledge as to 
 this has not yet been acquired. The computations of 
 Bretonniere relate only to the rectilinear part of the 
 course of the stork, so that he includes the parabolic 
 portion or the part in which the bird first falls by grav- 
 ity with a vertical movement and with accelerating speed 
 in order after that to go with a slight slope in which the 
 
 bird's movement and the inclination of its course appear by the 
 numerous observations not to vary in any marked degree, and with 
 a velocity of flight of twenty metres per second the inclination of 
 the line was equal to an angle with the horizon of ten degrees. 
 
HOVERING FLIGHT. 85 
 
 rate of fall is diminished. He considered oiily that por- 
 tion of the course in which the bird moves at a fixed 
 speed and at a fixed inclination, and while the movement 
 is regular in both respects. In illustration of these re- 
 marks, in the following sketch the direction of the wings 
 of a hovering bird are indicated by the heavy lines at A 
 and at B, the course of the bird's movement, at first 
 parabolic and afterwards rectilinear, by the dotted line 
 ABC, and the horizon by the dotted line D E. 
 
 M. Bretonniere now computed the two angles a and 
 f$ ; that formed by the direction of the wings and the 
 horizon a = 5, and that formed by the line of travel 
 
 FIG. 7. 
 
 /9 = 5 23' 11". Wherefore a-f /?, or the angle of the 
 line of travel with the horizon, amounts to about ten 
 degrees. 
 
 It is here to be remembered that when the combined 
 force, including the amount of air resistance caused by 
 
86 AfiRIAL NAVIGATION. 
 
 the sloping plane of the wings, is separated into a ver- 
 tical and a horizontal force, then, the more the angle of 
 the wing plane with the horizon increases that is, that 
 as the descent of the bird becomes steeper the hori- 
 zontal force in fact increases ; but, on the other hand, 
 the reacting vertical force which supports the bird in 
 the air decreases, so that it is compelled to fly faster. If 
 the bird were not able to comply with this condition, it 
 would not be sufficiently supported, and might lose its 
 balance. 
 
 If, on the other hand, we suppose the bird to be soar- 
 ing upward, then the sum of air resistance will increase 
 with the angle of the wing plane with the horizon, and, 
 consequently, the reacting horizontal force of this air 
 pressure must have a more and more retarding influence 
 on the flight. The momentum of the bird, already 
 established, whatever its origin, whether by falling or 
 by the use of the wings, would appear to be insufficient, 
 and to require increased air resistance through greater 
 velocity. 
 
 In order to reduce these considerations to figures, 
 Marey supposes a hovering plane of a certain size to be 
 placed at an angle with the horizon of ten degrees ; the 
 total vertical air pressure is taken as one hundred and 
 thirty-two grammes, and the horizontal pressure as fifteen 
 grammes. Then, if the weight to be supported is not more 
 than one hundred and thirty-two grammes, the angle of 
 ten degrees is sufficient. If, on the other hand, the 
 weight to be supported is greater for example, two 
 
HOVERING FLIGHT. 87 
 
 hundred and ten grammes then the reacting vertical 
 force of the air resistance must be made equal to the 
 weight. This is possible without changing the direc- 
 tion of the plane or its angle with the horizon, if only 
 the velocity of travel, and thereby the resistance of the 
 air, can be correspondingly increased. If, however, we 
 must maintain the same velocity, then, in order to in- 
 crease the resistance and the consequent vertical sup- 
 porting force, we shall be obliged to increase the angle 
 with the horizon to twenty-five degrees. This will, it is 
 true, carry the weight, two hundred and ten grammes, 
 but the retarding resistance of the air in a horizontal 
 direction will in like manner increase that is, to ninety- 
 five grammes and the horizontal velocity will decrease. 
 The angle of twenty-five degrees is thus less favourable 
 than one of ten degrees. In the case of a bird, the loss 
 of velocity always increases, and especially as a result of 
 its need to maintain its position against the force of 
 gravitation. In this it can indeed often succeed only by 
 flying faster, and in that case meeting less resistance to 
 its progress because it cuts the air at a sharper angle. It 
 will also lose less of the momentum which has been ac- 
 cumulated in its mass by the increased action of the 
 wings ; while it results from this that it requires in full 
 flight less effort for greater velocity than seems to be 
 needed for less velocity. 
 
 It is to be considered, further, that when the bird 
 flies upward the air is not brought under a pressure of 
 the upper side of the rising wing. If, indeed, the air 
 
88 AfiRIAL NAVIGATION. 
 
 were so pressed by the upper side of the wing from 
 below upward an upward current would be produced. 
 This, however, is not the case, for birds which fly up- 
 ward with great velocity turn their flight feathers on 
 their axes with wonderful skill, so that they cut the air 
 and create no pressure. If, however, the bird is in full 
 flight, then the turning of these feathers does not take 
 place. Neither does the folding of the wings with which 
 it is automatically connected ; so that the air pressure 
 on the upper side of the wings is dependent on 
 
 1. The relative velocity of the wind. 
 
 2. The rapidity of the lifting of the wings. 
 
 3. The slope of the surface of the wings. 
 
 The vertical reacting force of the air resistance under 
 the wings is regulated by the stroke, and this has also 
 been shown by various experiments. 
 

 CHAPTER XII. 
 
 SAILING FLIGHT. 
 
 THE sailing flight of birds corresponds in many re- 
 spects with hovering. It is possible only when the 
 wind can act on the under side of the wings. If there 
 is no wind, then the sailing bird must propel itself 
 through the air by the action of its wings, for it can fly 
 in no other way. 
 
 Sailing flight is confined to particular birds which 
 are, physically, peculiarly constituted for it. Those 
 best adapted for it have long, narrow, flat wings. For 
 this flight often only a light wind is required, as is seen 
 in the case of the frigate-bird and the Carolina kite, 
 which fly in regions where, according to Barte, the air 
 is comparatively calm. In regions where the wind is 
 stronger, only such birds can sail as have wings of 
 much less surface, as the common and larger gulls, 
 storm birds, and vultures. 
 
 The existence of wind is, nevertheless, an absolute 
 requirement for sailing flight; and while it has been 
 thought that birds were seen to sail in still air, it is 
 highly probable that while a calm reigns at the surface 
 
90 AfiRIAL NAVIGATION. 
 
 of the ground there must still be a wind in the higher 
 strata where they are.* 
 
 It is, however, to be remarked that many mechanics 
 have denied the possibility of this flight, and have con- 
 sidered it to be as chimerical as perpetual motion. 
 They considered that the name " sailing flight " indi- 
 cated an incorrect comparison, and that the bird in no- 
 wise fulfils the conditions of a sail-boat. In this, how- 
 ever, they were wrong, and it is fair to suppose that 
 they had never observed sailing flight correctly, for 
 much resemblance is to be observed between the sailing 
 of boats and the sailing flight of birds. It is only 
 necessary, in this connection, to take account of the 
 condition: that the wind strikes the sails of a boat 
 from the side, and the wings of a bird from under- 
 neath. 
 
 The wind which strikes the sails of a boat or the 
 wings of a bird at an acute angle is reflected from the 
 surface of either and flows away. It thereby creates 
 a counterbalancing force or reaction which sends the 
 
 * According to Barte, sailing flight on a wind of from three to 
 five metres per second (four and a half to seven and a half miles 
 per hour) requires a wing surface of fifty-five to sixty square 
 decimetres per kilogramme of weight, and in a wind of from nine 
 to twelve metres (nineteen to twenty-five miles per hour) a sur- 
 face of thirty to thirty-five square decimetres ; while in a gale of 
 twenty to twenty-five metres (forty to fifty-five miles per hour) 
 only such birds can fly as have wings of twenty-five to thirty 
 square decimetres per kilogramme. Barte, Memoire relatif au 
 Probleme de Locomotion dans VAir, I'Aeronaute, Octobre, 1872, 
 page 191. 
 
SAILING FLIGHT. 91 
 
 boat or the bird forward in a direction that is more or 
 less different from its own. 
 
 The sail-boat can sail so close to the wind only be- 
 cause its keel prevents it from leaving its course ; or, 
 in other words, it is thereby kept from giving away be- 
 fore the force of the wind. The action of the air on 
 the wings tends, according to their angle, to turn the 
 course of the bird upward, and this tendency, which is 
 called lifting propulsion, is more or less counterbal- 
 anced by the force of gravitation, according as the bird 
 desires to maintain the same height or to fly higher or 
 lower. The equivalent of the effect of the rudder, by 
 which a sail-boat is kept from falling away from its 
 course, the bird possesses in its tail, which it uses as a 
 rudder and also as a means for changing the position of 
 its centre of gravity. It will thus be understood that 
 the pressure of the wind has a tendency to turn the 
 bird and to tumble it over frontwise, and that this is 
 prevented by simply moving the centre of gravity to 
 the rear. Sail-boats and sailing birds are thus correctly 
 compared with each other; and, in fact, naval officers 
 who have watched this sailing flight acknowledge that 
 the study of sailing gives useful indications for the 
 elucidation of the flight of birds. 
 
 Based on considerations of this kind, D'Esterno, as 
 early as 1864, attempted to form a theory of sailing 
 flight. He was of the opinion that birds could not sail 
 against the wind without losing velocity. Other writ- 
 ers, however, have gone further. Mouillard had ob- 
 
92 AERIAL NAVIGATION. 
 
 served birds which were able from a state of rest in the 
 air to rise and go forward against the wind without a 
 stroke of the wings. 
 
 According to Audubon, the frigate-bird can make 
 head against a storm and hold its own position without 
 falling back. He also says that storm birds can rise 
 against the wind. Marey has likewise seen large gulls 
 begin with a sailing flight against a very strong wind, 
 though they then made very slow progress. According 
 to the testimony of all writers who have observed the 
 vertical rising of a bird in the face of the wind, this 
 manoeuvre requires a stiff breeze. If the wind is light, 
 then, according to Mouillard, the bird rises with a spiral 
 course. A circular line of travel therefore admits of 
 sailing flight in a breeze that is too light for a recti- 
 linear course. By means of such circling the eagle 
 maintains itself at a great height in the thin air. One 
 was observed by Humboldt himself at an elevation of 
 seventy-three hundred metres (twenty-four thousand 
 feet). Under these circumstances, I trust that the 
 theory of D'Esterno may be left to the future with its 
 further investigations. 
 
 In this connection I think it will be well to say a 
 word about the parachute, which belongs in a greater 
 or less degree to the outfit of the balloon. With the 
 parachute, courageous aeronauts in one case a woman 
 have ventured to leave the car at a giddy height and 
 descend to the earth. The parachute opens with the 
 fall, and when opened it meets so much resistance 
 
SAILING FLIGHT. 93 
 
 from the air that the ground is reached slowly and 
 without danger. Hanging from the parachute, a man 
 soars or sails downward and assumes in many re- 
 spects the conditions of soaring or sailing bird flight. 
 He can, in full compliance with the rules for sailing 
 a boat, determine the direction of the descent, and fix 
 with considerable accuracy the point at which the land- 
 ing shall be made. 
 
CHAPTER XIII. 
 
 THE LAW OF AVA^ZIJSTI. 
 
 THE centre of air pressure takes different positions 
 under the wings of the bird, according to the law of 
 Avanzini. 
 
 When a bird stretches its wings out horizontally to 
 descend vertically from an elevation, the centre of bear- 
 ing of the wings and the centre of air pressure coincide. 
 As soon, however, as the bird moves rapidly in a slant- 
 ing direction the centre of air pressure is transferred 
 to the hinder part of the wings, more and more so in 
 proportion as the flight becomes faster and as the an- 
 gle of the wing surface with the direction becomes 
 sharper. 
 
 This transferring of the centre of air pressure was 
 discovered by Avanzini in his experiments relative to 
 the resistance afforded by water when planes are moved 
 in it at different inclinations. 
 
 De Louvrie supposed that in the moving of a plane 
 in -a slanting direction through the air a resistance cor- 
 responding to that encountered in water must be created. 
 This is confirmed by the observation that a bird soaring 
 through the air at great speed carries its wings and con- 
 
THE LAW OF AVANZINI. 
 
 95 
 
 sequently its centre of gravity to the rear. In this case, 
 in order that the equilibrium may not be disturbed and 
 that the bird may not lose its balance, it follows that the 
 resultant of the air pressure must not fall on the centre 
 of the bird, but must also be transferred to the rear. 
 Cayley has in like manner maintained that this trans- 
 ferring of the centre of air pressure takes place when- 
 ever the wings are carried at a very acute angle with 
 the direction of flight.* 
 
 It also appears from the observations of M. Mouillard 
 that the direction of the wings is modified in accordance 
 with the velocity of soaring or travel. Birds that soar 
 very slowly carry their wings to the front, so that they 
 
 form an angle within which the head is placed as shown 
 in Fig. 8. Other birds which fly rapidly carry their 
 wings, on the other hand, to the rear, so that they form 
 an angle in front as shown in Fig. 9. 
 
 The changing of position of the centre of air pressure 
 
 * ISAeronaute, 1877, p. 260. 
 
96 
 
 AfiRIAL NAVIGATION. 
 
 under the wings of a rapidly soaring bird may suggest 
 the thought that a loss of balance is possible. Against 
 this danger the bird is able to provide in several ways ; 
 the tail, which acts as a rudder, may be turned vertically 
 upward, the wings may be carried backward, or, finally, 
 
 FIG. 9. 
 
 the neck may be stretched forward. The last is, for 
 example, to be seen in the case of the heron, which in 
 normal flight draws in its neck and holds its head be- 
 tween its shoulders, but which when pursued by a bird 
 of prey stretches out its neck and therewith increases 
 its speed. 
 
 The more the centre of gravity is thrown forward 
 the greater is the velocity of flight. This assumption is 
 based not only on what is observed in the case of birds, 
 but is also deduced from a series of observations with 
 hovering planes. Previously to these observations it was 
 attempted to reduce the hovering of birds to the simplest 
 form. A square of paper was with this view bent in the 
 middle so as to form an angle with two equal planes. In 
 the fold or angle a light needle was fastened with a little 
 
THE LAW OF AVANZINI. 
 
 97 
 
 wax, and this was loaded at the ends with small balls of 
 equal weight, so that when the apparatus was hung from 
 the middle in a horizontal position it was perfectly bal- 
 anced. As the centre of gravity now lies in the angle 
 and midway of the length, if the object is allowed to fall, 
 the outer edge of the fold will remain horizontal and 
 will be the lowest, as shown in Fig. 10. When, how- 
 ever, the ball is removed from one end and the centre of 
 gravity is thus transferred towards the other end, the 
 
 
 
 
 
 
 
 
 
 1 
 
 ' 
 FIG. 10. 
 
 FIG. 11. 
 
 object floats in a slanting direction, and descends with 
 increasing velocity towards the ground in the manner 
 shown in Fig. 11.* 
 
 The apparatus may also be made to assume a verti- 
 cal position as it descends, as when both leaves of the 
 bent sheet are turned down at the upper rear corner as 
 in Fig. 12. That is, the object, apparently in opposi- 
 
 * It is also asserted that a similar phenomenon is to be observed 
 in the steering of a boat. 
 
98 
 
 AERIAL NAVIGATION. 
 
 tion to gravitation, is seen at a given point of its side- 
 long descent to turn upward, which is accompanied 
 with a loss of velocity of movement. This has been ex- 
 plained by the fact that so long as the apparatus in 
 descending had attained little speed, the influence of 
 
 FIG. 12. 
 
 the curved course had not much effect; but, as the 
 speed increases, the apparatus acts as under the influ- 
 ence of a rudder and turns upward, as shown in the 
 figure. The force of gravity which had caused the in- 
 creasing velocity in the descent acts after the turning 
 as a retarding influence, so that the object is brought 
 to a standstill. 
 
 With a height sufficient to permit the experiment, 
 a second descent will follow, and a series of revolu- 
 tions may be observed before the apparatus reaches the 
 ground. 
 
 If the paper is arranged as shown in Fig. 13, with 
 curved instead of flat wings, then the apparatus will be 
 
THE LAW OP AVANZIXL 
 
 99 
 
 seen at a certain point, after descending a little, sud- 
 denly to change its course and to fall heavily towards 
 the ground. In this case, at the moment when the 
 rudder-like action was exhausted, the new direction was 
 helped by gravitation, aided rather than hindered by 
 the descent, as in the former case. 
 
 FIG. 13. 
 
 The movements of this little paper contrivance have 
 much resemblance to those of birds, and were it pos- 
 sible during its descent suddenly to change the shape 
 of the leaves, we might imitate the downward sweeping 
 and the upward turning of the falcon, as described in 
 Chapter XL* 
 
 * Soaring devices are made of various shapes and forms. The 
 aeroplane described by Cayley descended with a weight of two 
 hundred pounds from the heights to the plain at an angle of ten 
 degrees with the horizon. Pline constructed, twenty years ago, 
 curious light toys in the form of birds and butterflies, which, by 
 the bending or extending of the wings, thus slightly changing 
 
100 AfiRIAL NAVIGATION. 
 
 The importance of a close study of the little appli- 
 ances which imitate mechanically the flight of birds 
 may now be generally understood. Artificially con- 
 trived appliances of the character of those prepared in 
 1875 and 1877 by Alphonse Penaud and Tatin have 
 recently been taken up by Pichancourt, whose mechan- 
 ical birds, weighing twenty-five grammes, with waving 
 wings 0-35 metre wide, and with India-rubber feathers, 
 worked with great regularity. These appliances can 
 with a slow rising make a flight of some twenty metres' 
 length. A larger machine, weighing six hundred and 
 seventy-five grammes, when started forward by the 
 hand, reached by its own movement a height of twenty- 
 eight metres, and a distance of twenty-one metres 
 against the wind, notwithstanding its velocity was four 
 metres per second (over eight miles per hour). These 
 small mechanical appliances, it is true, are intended 
 chiefly for toys, but their regular working gives them 
 an unmistakable value for experiment and observation. 
 
 the centre of gravity, can be made to take on various movements, 
 going fast or slowly, smoothly or by fits and starts, and finally 
 straight or on a sweep. The movements of these little toys were, 
 because of their lightness, very slow, as the action of gravity 
 which gave them their motion was slight as compared with the 
 resistance of the air. Still, it was impossible, by reason of their 
 slow movements, to follow all of their various changes with the 
 eye or to distinguish all of their accelerations and retardations 
 during their course, which must be seen with accuracy in order 
 to understand soaring flight practically. This difficulty has now 
 been overcome, since photographic observations of soaring devices 
 have analyzed and determined them. 
 
CHAPTER XIV. 
 
 THE EXERTIOK OF FORCE BY BIRDS. 
 
 THAT birds consume or exert any force at all in 
 their soaring and sailing flight has often been doubted. 
 According to Mouillard, the old falconers observed that 
 falcons which sought to capture their prey, and in rising 
 flew out and back, exerted no force in the manoeuvre, 
 though this seemed to be the case at first sight. They 
 convinced themselves of this by watching the breath- 
 ing of the birds, which was little if at all accelerated 
 beyond what it was when only a few moments' use had 
 been made of the wings. 
 
 The falconers likewise thought that the bird was 
 also, so to speak, refreshed by the strong air currents 
 in which it had been roaming. The truth is, however, 
 that they had performed only the slightest mechanical 
 work. 
 
 As artificial bodies, corresponding in form with the 
 bird, properly balanced in the air, glide or float, and, in 
 proportion to the height at which they are released, 
 travel over considerable distances, so it appears that 
 these movements, which compare exactly with soaring 
 flight, require no exertion of force ; gravitation alone 
 
102 AfiRIAL NAVIGATION. 
 
 does the work^'in this case, which is shown by the de- 
 creasing elevation of the object above the ground, 
 Hcc'ording to the'* distance that it has travelled in its 
 floating. 
 
 Sailing flight is especially distinguished by a series 
 of soaring and " rowing " movements. The force of the 
 wind is here the source of power. In " rowing " flight 
 the pectoral muscles of the bird perform a negative 
 work. These great muscles offer a resistance to the 
 lifting of the wings, but they yield to the force of these 
 movements, and finally give way under it; just as a 
 man who takes a heavy object from a high place and 
 sets it on the ground, when his muscles are strained 
 against the weight, but in reality yield to it. 
 
 In soaring or sailing flight the bird has, theoret- 
 ically, exerted and consumed no force, because it per- 
 forms only an imperceptible movement in changing its 
 centre of gravity. Meanwhile it holds its wings out- 
 stretched in both soaring and sailing, so that the entire 
 weight of its body is upheld and supported by the re- 
 sistance of the air. The bird is, therefore, not inappro- 
 priately likened to an athlete, who, with straightened 
 outstretched arms, is able to hold himself up between 
 two points of support, although the whole weight of his 
 body is bearing upon them. In this case, also, no work, 
 or at least no perceptible work, is done, for the position 
 of the body is not changed ; yet the enormous exertion of 
 strength required under this strain is evident from the 
 fatigue that follows. 
 
THE EXERTION OF FORCE BY BIRDS. 103 
 
 The bird, when soaring or sailing, exerts a force 
 which may be compared with this that is, it carries 
 the weight of its body between its two outstretched 
 wings, whose points of support are at the centre of the 
 air pressure under them. Now, these centres of pressure 
 may, in soaring or sailing, lie much nearer to the body 
 of the bird than in " rowing " flight. Yet the force re- 
 quired for this flight is much less than that exerted by 
 the large muscles of the breast in supporting the soar- 
 ing bird. It is, therefore, very important to inquire 
 whether or not the pectoral muscles of sailing birds 
 have something special in their arrangement and oper- 
 ation that enables them to sustain the required ex- 
 ertion. 
 
CHAPTER XV. 
 
 ATMOSPHEKIC CUKKENTS. 
 
 IT is true that we can draw inferences as to the di- 
 rection of winds, and as to storms, from barometric vari- 
 ations, or from the atmospheric pressure at the surface 
 of the earth ; but no correct idea can thus be formed of 
 the currents which may prevail at different elevations, 
 resulting from the increasing rarity of successive strata. 
 With regard to this we are wandering in complete un- 
 certainty, for it has not yet been possible to determine 
 the influence of this rarity by observations. A contrary 
 belief formerly prevailed quite generally, that in the 
 higher strata the currents had fixed directions which 
 could be made serviceable in aerial navigation ; and that 
 at different elevations, currents, and counter-currents 
 existed, which would serve for going and coming in dif- 
 ferent directions. Though I doubt it very much, still the 
 possibility that such currents exist can as yet hardly be 
 contested with absolute certainty when we consider the 
 trade- winds and monsoons that exist elsewhere. Before 
 we can assume that they are so general, they must first 
 be established by observation and demonstration. The 
 currents in the strata cannot, however, be tested and 
 
ATMOSPHERIC CURRENTS. 105 
 
 determined without the aid of balloons or other means 
 of traversing the air, for observations taken from the 
 surface of the earth as to the direction of the movement 
 of clouds are still very uncertain. 
 
 Observations with appliances made for determining 
 the force and velocity of the wind at the surface can- 
 not be used for studying the movements of the upper 
 air, because the observer is immersed in this and is borne 
 along with it, while the anchoring of a balloon at a 
 great height has never yet been accomplished. The im- 
 portance of an exact knowledge of the meteorological 
 conditions of our atmosphere cannot, however, be de- 
 nied, but, as the foregoing remarks indicate, there are 
 great difficulties in the way of making observations in 
 the boundless air. It is worth while, nevertheless, to 
 call attention to observations made at about the same 
 period by Gay-Lussac in his scientific experiments with 
 the balloon in 1804, and by Saussure and Von Hum- 
 boldt in high Alpine regions. In later times many ob- 
 servatories have been built on high peaks, and in their 
 balloon ascensions Messrs. Glaisher, Gaston, and Tissan- 
 dier rendered important services to science. The ques- 
 tion has, therefore, presented itself as to the manner of 
 observation to which the greatest weight should be given 
 in seeking general knowledge of atmospheric phenomena. 
 
 Concerning this, however, there seems to be no room 
 for doubt that the condition of the atmosphere on high 
 mountains, in view of the temperature, the hygrometric 
 
 conditions, and the state of the wind, differs very much 
 
 8 
 
106 AfiRIAL NAVIGATION. 
 
 from that in the free air, so that the preference is to be 
 given to observations by which the free, high air can be 
 reached. 
 
 Meanwhile there are already sufficient indications 
 that meteorological observations taken on the Eiffel 
 Tower in Paris, where not only the horizontal but also 
 the vertical or up-and-down movements of the air are 
 being studied, will be of great value. In June, 1889, an 
 anemo-cinemographic apparatus was set up there by 
 which to observe the direction and the mean force of 
 the wind. A second and more complete apparatus, 
 made by the Brothers Richaud, was set up in October, 
 1891, by which the vertical movement was given by 
 means of a small wheel with four wings or screw blades 
 set, at a pitch of forty-five degrees, on a vertical axis, 
 and running in either direction, according as the result- 
 ant of the air current is upward or downward, while it 
 stands still under a horizontal wind of even the greatest 
 velocity.* 
 
 According to the new apparatus, on November 23 
 and 24, 1891, this velocity reached thirty-four metres 
 
 * Ordinary anemometers seldom suffice for these conditions. 
 They necessarily lead to the inference that the air pressure exerted 
 on the opposite wings will have the same velocity. In order to 
 obviate any source of error, or effect of external conditions, the 
 apparatus now used is placed in the axis of a vertical cylinder 
 twenty-five centimetres high (ten inches), which is open above and 
 below ; it is thus protected against the direct action of horizontal 
 currents, and seems to give satisfactory results. The velocity of 
 the wind is shown graphically on a strip of paper, which unwinds 
 at the rate of three centimetres per minute. 
 
ATMOSPHERIC CURRENTS. 1Q7 
 
 per second (about seventy-eight miles per hour) on the 
 morning of the 24th, and in less than thirty seconds 
 fell off to 19'9 metres per second (from seventy-eight 
 miles to forty-five miles per hour). The pressure, which 
 is as the square of the velocity, was thus reduced to 
 about one quarter in half a minute. 
 
 In this time the anemo-cinemograph gave the av- 
 erage velocity during a period of one minute as 26*3 
 metres (about fifty-eight miles per hour) ; while the 
 same apparatus, on January 23, 1890, indicated thirty- 
 two metres per second (about seventy-two miles per 
 hour) ; so that it was considered probable that the 
 greatest velocity reached was forty metres per second 
 (ninety miles per hour). 
 
 Thus far, the greatest vertical velocity on the Eiffel 
 Tower reached about 6*8 miles per hour (more than 
 three metres per second), on the 24th of November, 
 1890, between 10.30 and 11.30 in the morning, with 
 a rising wind. The horizontal velocity in the same 
 time reached 18'8 metres per second (about forty-one 
 miles per hour), giving, as the resultant of both of 
 these velocities, an increasing force with a velocity of 
 nineteen metres per second (about forty-two miles per 
 hour), with an angle of nineteen degrees with the hori- 
 zon. The observations on the Eiffel Tower have not 
 continued long enough for laws or inferences as to the 
 general conditions of the atmosphere to be deduced 
 from them ; so that I think we must limit ourselves to 
 these conclusions : 
 
108 AfiRIAL NAVIGATION. 
 
 1. Descending currents seem to be less frequent 
 than rising currents, and to have less velocity. 
 
 2. Every rapid and continued fall of the barometer 
 is accompanied by a more or less rising current of from 
 two to three metres per second (about four and a half 
 to six and a half miles per hour). The horizontal cur- 
 rent is then also strong, the sky is covered, and the 
 change of temperature is slight, so that the rising cur- 
 rent cannot be ascribed to the influence of an increas- 
 ing temperature of the tower itself. This occurs by 
 night as well as by day. 
 
 3. The relation of the amount of the resultant of 
 the horizontal and vertical force of the wind under dif- 
 ferent conditions cannot yet be sufficiently indicated. 
 The vertical velocity during the storm very often in- 
 creases, however, during the brief moment of calm fol- 
 lowing the blast. 
 
 4. The currents always rise during a rapid fall of 
 the barometer. During a rising barometer they some- 
 times rise and sometimes descend. The investigation 
 of these phenomena will probably yield important re- 
 sults when a sufficient number of observations to that 
 end shall have been collected. 
 
 5. The longest periods of descending currents have 
 been observed during very rapid rising of the barom- 
 eter, or during continued high pressures. There have 
 also been observed during such conditions successive 
 descending and rising currents, each continuing several 
 hours. 
 
CHAPTEE XVI. 
 
 THE APPLICATION OF THE PRINCIPLE " LE PLUS 
 LOUED QUE L'AIK." 
 
 THE principle "Le plus lourd que Vair" which was 
 considered in Chapter I, has many firm partisans. 
 These have not failed to urge their opinion for practi- 
 cal application, and it was further advanced by the 
 construction of several floating appliances. 
 
 These appliances were generally very different, and 
 were of various kinds. They may be grouped under 
 three classes : 
 
 1. The screw flyer (helicopterous). 
 
 2. The straight- winged (orthopterous). 
 
 3. The aeroplane. 
 
 The first apparatus of the screw character (helicop- 
 terous) was originally advocated by Vicomte Ponton 
 d'Amecourt, Lalandelle, Nadar, Forlamini, and others. 
 It was based on the application of one or more screws 
 with vertical or slightly inclined axes operated by a 
 sufficient motor.* The screws were depended on to de- 
 
 * The first idea of this movement had already been set forth 
 in an apparatus submitted to the French Academy in the latter 
 part of the last century by Messrs. Lannoy and Bienvenu. 
 
110 AERIAL NAVIGATION. 
 
 velop the resistance or motive power in the air which 
 was intended to support the apparatus and also to move 
 it forward. 
 
 Small toys made according to this plan were able to 
 maintain their position in the air for some moments. 
 When, however, account was taken of the power re- 
 quired to operate these screws in the air, it was soon 
 seen that no motive force as yet available would suffice 
 for the support of the necessary weight. The vertical 
 force developed in the shaft of the screw must at least 
 equal the weight of the apparatus to be supported 
 and propelled. According to the calculation of Drze- 
 wiecki,* however, this force applied to a horizontal 
 screw would suffice to support and propel an aeroplane 
 loaded with twenty or twenty-five times more weight 
 than could be allowed in the case of a vertical screw 
 machine. The operation of the last-named screw ap- 
 paratus, therefore, from the point of view of useful 
 work, was very unsatisfactory. 
 
 The second or straight-winged device (orthopter- 
 ous) aimed at an imitation of the rowing flight of birds, 
 according to the earlier conception of their movements. 
 It had two or four horizontal inclined wings, which 
 were set in motion by a light motor, and which, in 
 order to support the apparatus, must be successively 
 
 * See the various writings of S. Drzewiecki ; among others, 
 Les Oiseaux consider es comme des Aeroplanes animes and Le vol 
 Plane, published at Paris by E. Bernard & Co. The first paper is 
 out of print and I have tried in vain to get a sight of it. 
 
THE PRINCIPLE " LE PLUS LOURD QUE L'AIR." HI 
 
 raised and lowered. By this means the propulsion by 
 the inclination of the wings and the direction of the 
 movement by the tail were secured. In the first appli- 
 cation the wings were so arranged that, like the slats 
 of a window-blind, they opened in rising to obviate the 
 downward resistance of the air. It was fancied that 
 this would correspond with the action of the wings of 
 a bird. The erroneous opinion was entertained that the 
 flight feathers of the bird turned in their places when 
 the wings are lifted, so as to let the air pass through 
 freely. According to the investigations of Prof. Marey, 
 this earlier interpretation can no longer be maintained. 
 It is shown in Chapter XI that the flight feathers turn 
 on their axes only when the bird flies rapidly upward 
 not when it is in full flight. Greater attention must 
 therefore also be given to the movement of the wings 
 themselves, which during a descent are moved more to 
 the front, and during an ascent to the rear, describing 
 in their movement a sort of inclined ellipse ; the lower 
 edge of the wing is directed a little to the rear in de- 
 scending, and to the front in rising. 
 
 If we take account, further, of the resistance that a 
 plane of the size of a bird's wing encounters in the air 
 when it is depressed as rapidly as it is in practice, the 
 amount of the resistance will be found to be far below 
 the weight of the bird, which indicates an absurdity. 
 
 Calculations based on the unit of time are, as is 
 shown in Chapter X, not to be relied upon. Finally, 
 Drzewiecki has observed that the insufficiency of the 
 
112 AERIAL NAVIGATION. 
 
 normal centre of support of the bird can be shown by 
 direct proof if a plane of the size of a wing is moved up 
 and down with the rapidity of wing-strokes.* 
 
 These calculations and experiments had seriously 
 disturbed confidence in the theory of the straight- 
 winged apparatus (orthopterous). The important de- 
 ductions of Marey, set forth in Chapter. X, that the 
 resistance of the air due to the downward stroke of the 
 wings increases as the speed of the bird in a horizontal 
 direction becomes greater, had, however, been left out 
 of the consideration. From this Drzewiecki deduced, in 
 1885, the principle that the descending wing during the 
 flight of a bird assumes the condition of an aeroplane. 
 
 The movements of the bird had always been studied 
 under the supposition that it could hold itself motion- 
 less in the air ; and no account was taken of the moving 
 of the bird itself, although the velocity of this progress 
 is much greater than that of the wing-strokes. If, ac- 
 cording to the indications of Prof. Marey, we combine 
 the movement of the wings throughout their whole sweep 
 with the forward movement of the bird, then it appears 
 that the upper side of the wing stands at an angle with 
 the horizon both in rising and in descending, and that 
 this angle is substantially constant. The wing is thus 
 converted to the condition of a movable aeroplane, and 
 the under side of the body and tail of the bird to that 
 
 * Communication of Drzewiecki to the Imperial Technical So- 
 ciety of St. Petersburg, April 13, 1885. 
 
THE PRINCIPLE " LE PLUS LOURD QUE L'AIR." H3 
 
 of a fixed aeroplane. Therefore, if account is taken of 
 the rapid forward movement of the bird, then it appears 
 that the straight-winged system of flying machines in 
 correct relation to bird flight resolves itself, as it were, 
 into the aeroplane system ; and the first or screw flying 
 system assumes the same character. The three systems 
 so far correspond as to appear as one ; while together 
 they represent the principle "Le plus lourd que Vair" 
 
 We must henceforth regard the bird as an animated 
 aeroplane, which makes it possible that we may be able 
 to determine the mechanical laws governing artificial 
 flight, and that we may indicate the way by which we 
 shall reach the result of aerial navigation through an 
 investigation of this aspect of the question. We must 
 therefore also consider the aeroplane with regard to its 
 mechanical construction, the dimensions of its bearing 
 surface, its conditions and velocity of movement, the 
 weight to be carried, and the proportions of the sup- 
 porting surface to this, the angle with the horizon of 
 the plane itself and of its line of travel, the motive 
 power required to secure the movement, etc. Further- 
 more, in forming a theory of the aeroplane, it is neces- 
 sary to take accurate account of all questions relating 
 to the conditions of equilibrium, and to consider also 
 whether or not the observations of bird flight and the 
 resulting calculations made always accord with the in- 
 ference deduced therefrom. 
 
 For such scientific investigation we must start with a 
 simple supposition : that a horizontal aeroplane moves 
 
AERIAL NAVIGATION. 
 
 in a direction which, under a certain angle with the 
 horizon, creates a resistance in the air that is perpen- 
 dicular to the plane. This resistance is, therefore, a 
 function of the size or dimension of the plane, of the 
 velocity of its movements, and of the angle with which 
 the air comes in contact with it. It may, therefore, ac- 
 cording to Chapters IX and XI, be separated into a 
 vertical impulse and a horizontal force which offers a 
 resistance to the movement. 
 
 The flight of birds is also subject to this law : they 
 cannot maintain their position in the air without great 
 speed.* The correctness of these theoretical considera- 
 tions cannot well be disputed, yet their practical applica- 
 tion is difficult because of the lack of correct data as to 
 
 * The normal speed of birds increases with their weight and 
 decreases with the increase of the spread of their wings. 
 
 Ducks, which sometimes weigh eleven kilogrammes per square 
 metre, are obliged, in order to sustain themselves in the air, to fly 
 with much greater speed than swallows or larks, whose weight per 
 square metre is not more than 1-5 kilogramme. The swallow, the 
 pigeon, and many other birds, reduce the surface of their support- 
 ing planes as they increase the velocity of their flight, folding the 
 wings and tail ; when it is to be observed that the tail is not used 
 as a rudder, but as an auxiliary sail. 
 
 In the absence of the requisite velocity, birds cannot rise, as is 
 well known to sportsmen, and as is clearly shown in the experi- 
 ments of Marey, given in Chapter X. If the bird in its flight does 
 not attain its normal speed, it then stretches out its wings to the 
 utmost and spreads out its tail like a fan. If it has, on the other 
 hand, attained speed enough, then the wings are reduced to the 
 average spread, and the tail is closed. Drzewiecki concludes that, 
 according to the theory of the aeroplane, the work performed by 
 the bird in flying does not exceed the muscular effort of other 
 animals. 
 
THE PRINCIPLE " LE PLUS LOURD QUE L'AIR." H5 
 
 the resistance encountered in a fluid medium by surfaces 
 moving in an oblique direction. Nevertheless, it is pos- 
 sible, with the aid of the empirical formula of Colonel 
 Duchemin, to calculate a table of weights which a hori- 
 zontal aeroplane can carry per square metre, moving 
 through the air at different velocities and at different 
 angles ; also the power required to propel the plane at 
 the same velocities and angles. From these tables it has 
 been deduced that the greatest amount of work with the 
 least consumption of power coincides with an angle (of 
 incidence) with the horizon of 1 50' 45'', which is called 
 the " optima angle." Further observations and compu- 
 tations will probably establish this angle as the correct 
 one, and, according to Drzewiecki, will lead to the fol- 
 lowing inferences : 
 
 1. That the carrying power of the aeroplane is a 
 direct consequence of its forward movement at a slight 
 angle with the horizon, and originates in the vertical 
 force created by the resistance of the air. 
 
 2. That the work done in floating becomes directly 
 available for horizontal propulsion. 
 
 3. That so long as the position of the plane is main- 
 tained at the optima angle of incidence during the hori- 
 zontal movement the apparatus must have a uniform 
 speed, which is called the normal velocity, and is de- 
 pendent on the weight of the plane, so that a heavy 
 apparatus must move faster than a light one. 
 
 4. That the expenditure of force required for for- 
 ward propulsion corresponds with the normal velocity 
 
116 AERIAL NAVIGATION. 
 
 and the weight of the apparatus, so that the resistance 
 during the movement, per unit of load, is constant for 
 the normal velocity and the optima angle. Drzewiecki 
 estimates it from four to five per cent of the weight of 
 the apparatus, so that the horizontal force of one kilo- 
 gramme should yield a duty of twenty to twenty-five 
 kilogrammes. 
 
 In the movement of the aeroplane the maintaining 
 of its stabilit} T or of its dynamic equilibrium is to be 
 regarded as of great importance. According to the 
 observations of Avanzini (see Chapter XIII), and also 
 according to the direct observations of Joessel, the cen- 
 tre of the resistance is transferred towards the front when 
 a plane under changing angles of constantly increasing 
 acuteness is exposed to the pressure of running water. 
 This transference is sufficient to maintain substantially 
 the equilibrium of the plane, because the force of the 
 resistance and of the movement, acting on different 
 points, form a couple which gives the plane a proper 
 angle. In this connection we may refer to the various 
 observations and experiments made by Langley at Wash- 
 ington, Maxim at London, and Lilienthal at Berlin, and 
 we may therefore count on seeing this question brought 
 to a solution, which, however, will meet serious obstacles 
 because of the considerable expenses required for such 
 experiments. 
 
CHAPTER XVII. 
 
 CONCLUSION. 
 
 FROM the foregoing statements and considerations 
 we arrive at the following results as to air balloons : 
 
 1. That in 1855 Giffard tried to improve the art of 
 aerial navigation by a considerable increase in the length 
 of the balloon, which, however, resulted in great diffi- 
 culties and disappointments. To this there was applied 
 a motor which gave a propelling force of 3 -82 horse 
 power per assumed unit (one hundred square metres) of 
 cross section. 
 
 2. That in 1872 Dupuy de Lome contributed im- 
 portant improvements with a view to increasing the 
 stability of the balloon, and applied a small motor of 
 0-65 horse power, with a propelling force of 0-38 horse 
 power per unit of cross section. 
 
 3. That in 1883 Tissandier also resorted successfully 
 to a certain increase of the length of the balloon, and 
 applied a propelling force of 2 horse power per unit of 
 cross section. And, finally 
 
 4. That in 1885, by means of several improvements, 
 there was found to be no difficulty in re-establishing 
 nearly the increased length of the balloon attempted 
 
118 AERIAL NAVIGATION. 
 
 by Giffard in 1855 ; and that with a motor of one quar- 
 ter the former weight there was obtained a propelling 
 power amounting to eight times that of Tissandier. 
 Furthermore, the balloon of Renard and Krebs, made 
 at the arsenal of Chalais, attained the important result 
 that in seven ascents a return was five times made to 
 the point of departure, showing that they five times had 
 complete control of its direction. A speed of 6 -5 metres 
 per second (about fourteen miles per hour) was reached, 
 showing that, according to the table in Chapter V, it may 
 be fairly estimated that during four hundred and fifty 
 hours out of one thousand this balloon could, with more 
 or less completeness, be driven in any direction. As 
 compared with the results of 1884, the speed was nearly 
 doubled, and the motive force was carried to nearly 
 eight times that of Tissandier. 
 
 These results are important, for in aerial navigation 
 velocity is of much more consequence than lifting 
 power, which for many reasons is always limited. In 
 aerial navigation, as is shown in Chapter V, we can con- 
 trol direction only by velocity ; and, indeed, it has also 
 been shown that the flight of birds is especially depend- 
 ent on velocity. It further appears, from the communi- 
 cations of Commandant Eenard, that an effort is now 
 being made at Chalais to double the velocity, and so 
 to carry it to thirteen metres per second (about twenty- 
 nine miles per hour). If, in strict accordance with 
 Chapter V, it is assumed that a velocity of 12'5 metres 
 per second (27'96 miles per hour) is sufficient, and that 
 
CONCLUSION. 
 
 the power of the motor is as the cube of the velocity, 
 then we have for the increased velocity of the Chalais 
 
 12'5 3 
 balloon a power of 8 X rr^ or about fifty-seven horse 
 
 D'O 
 
 power, which is a very satisfactory result. 
 
 Applying again the tables of Chapter V, we can esti- 
 mate approximately that with this speed during eight 
 hundred and fifteen hours in one thousand we may 
 move in any direction, and we may count on a speed 
 of twenty-five metres per second (about five and a half 
 miles per hour) during seven hundred and eight hours 
 in one thousand. In view of the exceptionally compe- 
 tent opinion of Commandant Renard, I do not doubt 
 that such a speed can be attained. It is not necessary 
 to adhere exactly to the dimensions and arrangements of 
 the Chalais balloon, and we may even secure an increase 
 of speed by various improvements. In spite of all this, 
 the weight of the motor required for such great power 
 must constitute a serious embarrassment, and, with due 
 respect for the opinion of Renard, I venture to think 
 that the solution of this difficult problem is perhaps not 
 to be expected at an early date. 
 
 A balloon in moving against the wind is further ex- 
 posed to the combined influence of the two opposed 
 forces with the great velocities of thirty-six and nine 
 kilometres per hour. Even if able to withstand this, 
 the velocity now secured cannot be regarded as sufficient 
 for the future ; and so the question comes more and 
 more seriously to the front, whether or not a balloon 
 
120 AERIAL NAVIGATION. 
 
 constructed of light material can be so made as to resist 
 the combined force of the air pressures. Thus far this 
 may be greatly doubted; and though the expectations 
 of Commandant Renard may be satisfied up to a certain 
 point, still the truly magnificent aim of navigating the 
 air with balloons may not yet be reached, because they 
 cannot be propelled with sufficient velocity to meet all 
 conditions of wind. This does not mean that the con- 
 tinuance of the observations of Renard and Krebs on 
 air balloons is not much to be desired at this time ; for 
 the scientific results to be expected from their investi- 
 gations will benefit not only the art of ballooning, but 
 that of aerial navigation generally. 
 
 Under these circumstances we may anticipate that 
 the balloon will give place to flying machines made on 
 the principle " le plus lourd que Vair" which has the 
 advantage that we shall be no longer dependent on the 
 limited time to which the use of gas with balloons re- 
 stricts us. We must, however, in the application of this 
 principle, at the outset keep it clearly in mind that the 
 apparatus must be as light as possible, and that it must 
 be driven at the highest possible speed. We must, fur- 
 thermore, consider closely the laws regulating the flight 
 of birds, and apply them more and more accurately as 
 continued investigation develops them. Constructors, 
 however, need not disturb themselves as to this. We 
 already know, especially from the scientific investiga- 
 tions of Prof. Marey, how Nature has outlined the so- 
 lution of the problem in the flying of birds ; and it is 
 
CONCLUSION. 121 
 
 evident that in the application of natural laws to aerial 
 navigation we cannot follow them blindly. Drzewiecki 
 has very justly observed that birds perform two very 
 distinct operations with the same organ ; for the wings, 
 by a wonderfully simple combination, form both an 
 aeroplane the extent of whose surface, whose position 
 and whose angle are changed at pleasure and a mo- 
 tive power whose greater or less activity is under con- 
 trol. Birds, also, when descending towards the earth, 
 can draw in their wings without in the least endanger- 
 ing their safety. 
 
 This is very remarkable, and worthy of close study. 
 For the present I shall be excused if I confine myself to 
 the remark that the combination of these different con- 
 ditions in a single organ is necessary to the bird in view 
 of the natural laws relating to vertebrate animals. Al- 
 ternate or " rowing " flight has been shown in the case 
 of small birds to possess advantages which it has not 
 in the case of larger ones with long wings and great 
 weight. This is also the reason why large birds confine 
 themselves especially to sailing and hovering flights. 
 For this, no continuous propulsion, and consequently no 
 up-and-down movement of the large wings, is required, 
 and wing-strokes in the case of such birds seem to call 
 for much exertion. 
 
 From the indications of Drzewiecki it further ap- 
 pears : 
 
 1. That a heavy flying machine must clearly be sup- 
 ported by an aeroplane of considerable dimensions. 
 
122 AfiRIAL NAVIGATION. 
 
 2. That this aeroplane must not be used as a motive 
 force, while the power developed by the different " row- 
 ing motions " would, because of the low velocity, be very 
 slight. Furthermore, that the construction of this aero- 
 plane would have to be very strong, giving considerable 
 dead weight. 
 
 3. That, according to the foregoing, it will be well, 
 in any case, to provide a special motor, working unin- 
 terruptedly, as, for example, is the case with the screw 
 propeller. 
 
 4. That in the movement of the (rowing) aeroplane 
 it would necessarily result that the mutual relation of 
 the centre of air resistance and the centre of gravity 
 would be continually changing, which would endanger 
 the stability of the apparatus. This change is, in the 
 case of the bird, constantly regulated by the sinews; 
 while with a flying machine it would require a very 
 complicated automatic apparatus, which, even with the 
 most extreme sensitiveness, could never be compared 
 with the perfect combination of the living bird. 
 
 With an immovable aeroplane and independent pro- 
 pelling screws, the varying positions of the centres 
 named will, on the other hand, become fixed, and the 
 stability of the aeroplane can be secured for a deter- 
 mined angle. 
 
 Drzewiecki has, therefore, recommended for the 
 construction of the flying machine a simple aeroplane 
 comparable to the outstretched wings of a large soaring 
 bird, placed on a framework with wheels on which it 
 
CONCLUSION. 123 
 
 may be rolled along until it acquires the velocity needed 
 to raise it from the ground ; also a light motor, suffi- 
 cient to drive a screw that will support the apparatus in 
 the air. The various movements in the machine due 
 to the changes of the centre of gravity, and the normal 
 velocity, with the force required for horizontal propul- 
 sion, must be regulated by bringing the apparatus into 
 a correct relation with the supporting surface of the 
 aeroplane. 
 
 Very light motors have already been made, and by 
 the use of hydrocarbon compounds an effective power 
 can be produced with little weight; while modern in- 
 genuity has by no means said its last word on this 
 subject. 
 
 Moreover, it can no longer be denied that the ques- 
 tion of aerial navigation has now assumed a really sci- 
 entific character. It may, therefore, be supposed that 
 the great problem will be carried to a complete solu- 
 tion ; still, at the outset, nothing more will be attempt- 
 ed than a flying machine suited to carry only a very 
 limited number of persons. These will be, as indeed 
 was the case in the first navigation of water, only skiffs 
 and small boats, which, however, will be able to render 
 valuable service in meteorological, military, and various 
 other fields, as for postal work, etc. It is, of course, not 
 to be expected that these skiffs will escape the law of the 
 evolution that grows out of necessity, as has been the 
 case with all means of transportation on the earth. At 
 the same time, we cannot, without seeming to paint a 
 
124 AfiRIAL NAVIGATION. 
 
 lively picture after the manner of Jules Verne, imagine 
 the growth of these skiffs into vessels carrying valuable 
 freight or into war vessels and monitors, so that the 
 wish must involuntarily come to our clever sailors that 
 it may be granted to them to sail in air ships to higher 
 spheres. 
 
 In conclusion, may I further observe that rapid 
 travel in the free air need encounter no serious diffi- 
 culty ! 
 
 ARCACHON, May, 1892. 
 
EXTRACTS FROM A LATER PAMPHLET 
 BY MR. FIJNJE. 
 
 AFTER the publication of his original pamphlet, the 
 author received a copy of Experiments in Aero-Dynam- 
 ics, by Prof. S. P. Langley, of- the Smithsonian Insti- 
 tution, and, based on this and on other more recent 
 writings, he wrote a second pamphlet as an extension 
 of it. 
 
 The new pamphlet begins thus : " Since the appear- 
 ance of my first observations on aerial navigation, this 
 subject has made an important advance, especially as a 
 result of the investigations of Prof. S. P. Langley, of 
 Washington. Recurring to what I then wrote, I am 
 glad to see that I need to retreat from none of my for- 
 mer conclusions, and that, on the contrary, I can main- 
 tain them without fear. The agreement is remarkable 
 between the conclusions that I advanced and those 
 which Prof. Langley has set forth in his important ex- 
 periments, and, which appear in his paper on Mechan- 
 ical Flight." 
 
 [The following extracts from this more recent publi- 
 cation relate largely to details of Prof. Langley's experi- 
 ments. They are followed by somewhat copious ex- 
 
126 AERIAL NAVIGATION. 
 
 tracts, of a general character, from Prof. Langley's own 
 report.] Translator. 
 
 In considering the various opinions as to soaring 
 and sailing flight, I am met by an insurmountable diffi- 
 culty when I try to regard the two methods of flying as 
 one, according to the German students of the subject. 
 In relation to this I cannot accord the same value to 
 the German opinion as to that which seems to have 
 been developed by Prof. Marey. In support of this 
 statement, I will recall from my earlier pamphlets only : 
 
 1. That soaring flight takes place only in a calm, 
 and must be due to and maintained by the weight of 
 the bird ; and, on the other hand 
 
 2. That sailing flight is possible only with prefer- 
 ably the strongest practicable wind, and is impeded by 
 the gravity or weight of the bird. 
 
 Now, the result of both of these methods of flight 
 may show great apparent similarity, but, on comparing 
 the directly opposite causes to which the two are due, I 
 can conceive no clear idea of their identity. Neither 
 can I agree with the opinion that the flight of birds is 
 not subject to the same natural laws that control me- 
 chanical flight. Still, we must not leave out of the 
 consideration the ability of the bird so to exert its mus- 
 cular power as to cause more or less increase of its 
 weight. Birds also have the important advantage that 
 they can increase their normal speed with their weight, 
 and can reduce it in more rapid flight. 
 
 Ducks, which must sometimes carry eleven kilo- 
 
EXTRACTS FROM A LATER PAMPHLET. 127 
 
 grammes per square metre, are thereby obliged, in 
 order to maintain their position in the air, to fly with 
 much greater velocity than swallows and larks, whose 
 weight per square metre is rarely more than 1'5 kilo- 
 grammes. The swallow, the pigeon, and many other 
 birds even reduce the area of their supporting surfaces 
 when they increase their speed by drawing in their 
 wings and closing their tails. 
 
 [After referring to the fact that in railway travel 
 heavy trains may be drawn at great speed if locomotives 
 are made heavy enough to develop the necessary friction 
 on the rail, and that in water transportation increased 
 service is secured by the use of larger vessels of suitable 
 draft, the author says :] Translator. 
 
 The increasing carrying capacity of railroad trains 
 and of vessels is in proportion to an increase of the size 
 and weight of the means of transportation. Whether 
 or not this principle can be regarded as applicable to 
 aerial navigation cannot now be determined, but it is 
 not likely that mechanical flight can be excluded from 
 the operation of this general law. We are only now 
 justified in expressing a preference for such appliances 
 for navigating the air as are heavier than the air that 
 they displace ; but as these find for the development of 
 their capacity no support, as on rails or in water, they 
 will require at the outset great rapidity of movement 
 and the least possible weight in order to maintain their 
 position in the air. We must also consider the difficulty 
 that we are limited in the power we can use for propul- 
 
128 AfiRIAL NAVIGATION. 
 
 sion and for maintaining the stability of the floating 
 machine. 
 
 The remarkable investigations of Prof. Langley are 
 especially important in this connection. Aerial naviga- 
 tion has thereby been enabled to enter on a new phase, 
 one which must lead to a solution of the question. 
 
 These investigations relate in general to the resist- 
 ance of layers of air to flat aeroplanes, propelled hori- 
 zontally under different conditions, or which fall by 
 gravitation, and to the air resistance created by the re- 
 volving of a propelling screw. 
 
 Langley, in developing the velocity desired for his 
 experiments, employed a swinging lever (" turn-table " 
 or " whirling-table ") 18-30 metres long. With the use 
 of a teu-horse-power engine a velocity of 30-15 metres 
 per second was given to the end of the lever, equal to 
 about 108*5 kilometres per hour (about seventy miles). 
 The apparatus was arranged for velocities from 4'5 to 
 forty-five metres per second,* and the actual velocity 
 was registered by an electrical appliance. The principle 
 was adopted that when an object is moved through the 
 air at a given velocity it has to resist the same pressure 
 that it would be exposed to in a wind of the same ve- 
 locity. In accordance with this principle, it was found 
 
 * That is. Prof. Langley says : " but owing to the slipping of 
 belts the number of turn-table revolutions was less than this for 
 the higher velocities, so that the highest attained in the experi- 
 ments did not reach this upper limit, but was a little over one 
 hundred feet (thirty metres) per second, or about seventy miles 
 per hour." Translator. 
 
EXTRACTS FROM A LATER PAMPHLET. 129 
 
 possible, by the use of extremely sensitive and ingen- 
 ious appliances, to establish the resistance caused by 
 the horizontal movement, or by the falling of the aero- 
 planes through the air. 
 
 In the experiments the aeroplanes were fixed exactly 
 horizontal, or at various angles with the horizon, and 
 provision was made for observing the time required for 
 a fall through a height of 1-22 metres (four feet). 
 
 The apparatus was so arranged that the centrifugal 
 force could exert no disturbing influence. With regard 
 to the other influence that a circular movement might 
 exert, through its effect on the circulation of the air, 
 which can be determined only by elaborate experiments 
 the formulae suggested thereon cannot be relied upon 
 Prof. Langley judged this influence to be negligible, 
 as he shows by an appropriate example, . . . indicating 
 that the difference appears so small that the average 
 pressure on the outer edge, and so much more on the 
 whole plane, may be assumed to be the pressure, and 
 consequently the velocity, at the centre. The principle 
 here involved will be considered further on. 
 
 The planes used in the experiments, which must 
 necessarily have a certain thickness, were cut off square. 
 The values obtained from them were thereby easier to 
 calculate, but they were not so favourable as if the angles 
 had been rounded off, or if the thickness had been grad- 
 ually reduced to a section according with "stream- 
 lines." 
 
 The friction of the air on the surface may, as 
 
130 AfiRIAL NAVIGATION. 
 
 was shown by the experiments, be disregarded. It 
 was calculated at y^ the part of the pressure ex- 
 erted on the aeroplanes at the speeds under consid- 
 eration. 
 
 From considerations of cost the observations were 
 taken in the open air, and therefore the conditions were 
 most favorable in calm weather, for in a confined build- 
 ing the air assumes a slow movement and forms eddies. 
 In practice, however, the open air is almost never at 
 rest, and the observations were greatly delayed for this 
 reason. An octagonal fence twenty feet high resulted 
 in no improvement, and Prof. Langley advises that at 
 all costs a large, completely enclosed building be used 
 for future experiments. This building should furnish 
 ample space. 
 
 It is to be remembered that these observations were 
 undertaken at a time when all the renowned natural 
 philosophers had asserted that the force required for 
 horizontal flight is equal to the sum of that needed to 
 uphold the object motionless in the air and that re- 
 quired to move it against the resistance of the air. 
 According to this, the force required must increase with 
 the velocity of movement. 
 
 The opposite, however, is shown by Prof. Langley's 
 observations. In the horizontal movement of aeroplanes 
 of equal size and weight, fixed at such an angle that 
 they would sustain themselves at a given velocity, it 
 was found that the propelling force needed for this 
 movement decreased as the velocity increased, so that 
 
EXTRACTS FROM A LATER PAMPHLET, 
 
 the earlier theoretical considerations would never have 
 led to a solution of the question. 
 
 The most important thing to be kept in mind is to be 
 found in the results of the experiments, which are given 
 at length, and concerning which it may be premised : 
 
 1. That the velocities were determined by exact ob- 
 servations of the time required for the revolutions (of 
 the whirling-table) ; and 
 
 2. That the wind pressures were established by exact 
 measurements of the different deviations from the cen- 
 tre, as they were indicated by a recording pencil point, 
 and which are the result of the velocity reached by the 
 end of the lever. To this end the amounts of the de- 
 viations were found experimentally by the use of differ- 
 ent weights. 
 
 Here follows a series of tables of mathematical cal- 
 culations, for which the reader is referred to Prof. 
 Langley's report.* They relate to trials of aeroplanes 
 of different shapes, set in pairs, the support at the end 
 of the lever being between them. The planes had each, 
 except the last one, an area of half a square foot one 
 square foot for each pair. Their dimensions were : 
 
 6 inches by 12 inches, f weighing per pair 123 grammes. 
 8 " 6 " " " 114 " 
 
 * See Smithsonian Contributions to Knowledge, vol. xxvii. 
 
 f The first measurement refers to the advancing edge. In 
 other words, the first two pairs travelled with the narrow edge in 
 front, and the others with the broad edge in front. 
 
132 AfiRIAL NAVIGATION. 
 
 12 inches by 9 inches, weighing per pair 115 grammes. 
 18 " 4 " " " 114 " 
 
 15 " 4 " " "' 118 " 
 
 The planes were set level or at various angles with 
 the horizon, they were at rest or propelled at different 
 velocities, and the results are indicated in the tables. 
 For example with the pair last described in the above 
 enumeration with a total front line of thirty inches 
 and a width (in the direction of movement) of four 
 inches, the planes at rest and horizontal dropped four 
 feet in O69 second. At an angle of one degree and 
 with a velocity of 24*6 metres per second, they fell in 
 2 '20 seconds and then soared. With a velocity of 23*3 
 metres per second at an angle of one degree, they " fell 
 slowly" (in 6-15 seconds). With a velocity of 20-9 
 metres per second, at an angle of two degrees, they 
 soared and then fell in 4-15 seconds. With a velocity 
 of 22-8 metres per second and an angle of two degrees, 
 they fell in 5*80 seconds. W^ith a velocity of 23 '7 metres 
 per second and an angle of three degrees, they stayed at 
 the top. 
 
 In a table to determine "horizontal velocities at 
 which inclined planes are supported by the air," it is 
 shown that a pair of planes of the third dimensions 
 given, having a front reach of twenty -four inches 
 and a width in the line of travel of six inches, when 
 set at an angle of twenty-five degrees soared at a 
 velocity of 11*0 metres per second, at an angle of six 
 
EXTRACTS FROM A LATER PAMPHLET. 133 
 
 degrees with a velocity of 16'2 metres per second, and 
 at an angle of five degrees with a velocity of 18-7 per 
 second. 
 
 By reversing the position according to the meas- 
 urement first indicated, giving a total front length of 
 twelve inches and a width of twelve inches, at an an- 
 gle of 
 
 30, the required velocity was 10 -5 metres per second ; 
 20, " " 12-3 " " 
 
 15, " " 14-7 " " 
 
 13, " " 16-2 " " 
 
 9, " " 21-2 " " 
 
 From these tables the author makes the following 
 deductions : 
 
 1. That the duration of the fall of the aeroplane 
 is greater in proportion as its advancing edge is .greater 
 than the width. It is therefore clear that the volume 
 of air of which the inertia is to be overcome by the 
 movement of the aeroplane increases : 
 
 (a) With an increase of the edge of the plane that is 
 perpendicular to the line of travel ; and 
 
 (b) With the velocity of movement. 
 
 This result is not surprising, and is illustrated by the 
 familiar example of a skater, who at high speed can 
 cross a sheet of ice that would not bear him if standing 
 still ; while ice is sometimes in a condition to bear two 
 skaters moving side by side, when it would give way if 
 one followed the other. 
 
134 AfiRIAL NAVIGATION. 
 
 2. That as the horizontal velocity of movement be- 
 comes greater, it takes less force to support the object 
 in the air than to maintain its velocity. 
 
 3. That the resistance to the air of two pairs of aero- 
 planes, placed at a sufficient relative distance above each 
 other, is double that of one pair, but that with an insuf- 
 ficient separation, say five centimetres for the planes 
 used, it may be less. 
 
 4. That the velocities in these experiments were often 
 grouped under those from 5 to 8 metres, from 12'5 
 to 13-5 metres, and from 22-5 to 24 metres per second. 
 With a velocity of twenty- three metres per second, the 
 time of falling (four feet) of two pairs of aeroplanes at 
 the respective distances from each other of 15 -2 and 10-2 
 centimetres, was sometimes the same as for single pairs. 
 The case was different when the separation was only 5'1 
 centimetres. 
 
 In order, independently of any formula, to establish 
 by direct observation the fact that the force required for 
 horizontal soaring becomes less in proportion as the 
 velocity increases, Prof. Langley used what he called a 
 self-registering component-pressure recorder.* 
 
 A series of tables is now given, for which the reader 
 is referred to Smithsonian Contributions to Knowledge, 
 vol. xxvii. The last is as follows : 
 
 * For a description of this, see Prof. Langley's report. 
 
EXTRACTS FROM A LATER PAMPHLET. 135 
 
 
 
 
 
 Weight with 
 
 Angle 
 with 
 hori- 
 zon. 
 
 Soaring speed. 
 
 Hori- 
 zontal 
 pressure. 
 K. 
 
 Work expended 
 per minute. 
 60 RV. 
 
 planes of like 
 form that one 
 horse power will 
 drive through the 
 
 
 
 
 
 air at velocity V. 
 
 
 Metres per Feet per 
 
 
 KUogram- 
 
 Foot- 
 
 Kilo- 
 
 
 
 second. second. 
 
 
 metres. 
 
 pound*. 
 
 grammes. 
 
 
 45 
 
 11-2 1 36-7 
 
 500 
 
 336 
 
 2,434 
 
 6-8 
 
 15 
 
 30 
 
 10-6 ! 34-8 
 
 275 
 
 175 
 
 1,268 
 
 13-0 
 
 29 
 
 15 
 
 10-2 36-7 
 
 128 
 
 86 
 
 623 
 
 26-5 
 
 58 
 
 10 
 
 12-4 i 40-7 
 
 88 
 
 65 
 
 474 
 
 34-8 
 
 77 
 
 5 
 
 15-2 49-8 
 
 45 
 
 41 
 
 297 
 
 55-5 
 
 122 
 
 2 
 
 20-0 65-6 
 
 20 
 
 24 
 
 174 
 
 95-0 
 
 209 
 
 The author then continues : 
 
 A uniform supporting power per square unit is as- 
 sumed when, with increased dimensions, the form and 
 inclination of the aeroplane remain the same.* 
 
 The determination of the propelling power exerted 
 by the whirling arm, and the estimate of the amount of 
 useful work there done, could be arrived at only experi- 
 
 * Prof. Langley says : " This, strictly speaking, holds good 
 only for a system of planes whose weight, inclusive of any actual 
 motor or other attached weight, is five hundred grammes per 
 square foot of inclined plane surface, and which is made up of 
 30 x 4 - 8 inch planes. The experiments with the plane-dropper 
 show that in horizontal flight, at attainable speeds, a system of 
 such planes can be made by placing one above the other at a dis- 
 tance of about four inches without any sensible diminution of rela- 
 tive efficiency. Whether these relations of power, area, weight, 
 and speed, experimentally established for small planes, will hold 
 good in the same ratios for indefinitely large ones, I am not pre- 
 pared to say ; but from all the circumstances of experiment I can 
 entertain no doubt that they do so hold far enough to afford entire 
 assurance that we can thus transport (with fuel for a considerable 
 journey) weights many times greater than that of a man." 
 
136 AERIAL NAVIGATION. 
 
 mentally. Prof. Langley limited his investigations to 
 screw propellers, not because they were the only prac- 
 ticable device for propulsion, but because they seemed 
 to offer the most important advantages for this purpose 
 and for reasons of convenience. For this investiga- 
 tion he prepared a dynamometer-chronograph, by which 
 the driving force and the actual work done were indi- 
 cated by a self-registering apparatus, in which three 
 pencil points traced separate lines on a cylinder moved 
 by clockwork. 
 
 It was necessary to take into account the renewal of 
 the air in contact with the blades of the propeller, as 
 this has a great influence on the amount of useful work 
 and on the exertion of force in the direction of the 
 shaft or end thrust. If a screw, working on a fixed 
 support, is revolving in still air, a portion of its work 
 will be expended and a certain force exerted in the di- 
 rection of its axis. If the screw is then subjected to 
 the action of a wind blowing parallel to its axis, then, 
 for the same consumption of power, the end thrust will 
 be increased. There is a perceptible wind in a direc- 
 tion parallel to the axis when the apparatus is driven 
 through the air, and effects observed are greatly influ- 
 enced thereby. This influence can be measured by 
 a dynamometer placed at the end of the whirling 
 lever. 
 
 Prof. Langley first used in his experiments wooden 
 screws with four, six, or eight blades, pitched at va- 
 rious angles ; and afterwards two aluminum screws 
 
EXTRACTS FROM A LATER PAMPHLET. 137 
 
 of twenty-four inches and thirty inches diameter re- 
 spectively. 
 
 The observations, with an aluminum screw having 
 two blades and a diameter of thirty inches, the blades 
 being pitched at an angle of seventy-five degrees with 
 the axis, gave the following results : 
 
 Speed of screws, 1,032 revolutions per minute. 
 
 Velocity of dynamometer drum, 1,063 feet per 
 minute. 
 
 Power developed in the direction of the shaft, 0-20 
 pound. 
 
 Work done, being the speed of the whirling arm 
 multiplied by the end thrust, 373 foot-pounds per 
 minute. 
 
 The work done is thus about one half of the actual 
 power. 
 
 It is to be remarked in this connection that a screw 
 with two blades has the maximum efficiency (as a pro- 
 peller in air), in contradistinction to a windmill, where 
 both practice and theory have shown that, so far as is 
 practicable, the whole circle should be furnished with 
 blades. 
 
 With a screw propeller, the air is met by each blade 
 after it has yielded to the pressure of the previous 
 blade, and cannot, because of loss of inertia, offer so 
 much resistance as if it were still at rest as was sug- 
 gested in my earlier observations on the rowing flight 
 of birds. 
 
 The greater the velocity of advance, the less the 
 10 
 
138 AERIAL NAVIGATION. 
 
 amount of back-flow * and the more effective the work- 
 ing of the screw. 
 
 It would appear from the investigations of Prof. 
 Langley that the resultant of the pressure exerted on a 
 moving plane is perpendicular, and that the following 
 deductions may be made : 
 
 1. That less force is required to support a body in 
 the air when it is moving horizontally than when it is 
 at rest. 
 
 2. That this force diminishes with the increase of 
 velocity of lateral movement ; and that, therefore, the 
 power needed to maintain the soaring of inclined planes 
 will apparently lessen as the velocity increases. 
 
 3. That the length of time occupied by the fall of 
 horizontal planes increases as their lateral travel grows 
 faster, and that the time will increase as the edge 
 of the plane that is at right anges to the line of 
 travel is longer than the edges that are parallel to 
 this line. 
 
 4. That the power required to maintain the horizon- 
 tal velocity of a soaring plane, set at an angle, dimin- 
 ishes with increased speed. 
 
 5. That aeroplanes set one above another exert no 
 unfavourable effect on each other if they are separated 
 
 * By back-flow (" slip ") is meant the difference between the 
 actual velocity of advance and the velocity that would be secured 
 if the propeller were working in immovable air, like a common 
 screw in a solid nut. 
 
EXTRACTS FROM A LATER PAMPHLET. 139 
 
 by a distance at least equal to the length of the edge 
 that is parallel to the line of travel. 
 
 This condition is practically the most noteworthy, 
 because it indicates that we may avoid the difficulties 
 attending the use of very large aeroplanes. 
 
 Finally, the possibility is demonstrated of causing 
 inclined aeroplanes to soar at a velocity of about twenty 
 metres per second (about forty-four miles per hour), 
 with a load of about ninety kilogrammes (about one 
 hundred and ninety-seven pounds) per horse power. 
 At the same time it is to be noted that we have steam 
 motors weighing less than ten pounds per horse power, 
 and that the weight that aeroplanes will have to carry 
 is not more than ten per cent of what the investigations 
 in question have shown. We may therefore assume 
 that the above rules will be applicable to planes of 
 larger dimensions, though we cannot yet assert that 
 objects are to be carried soaring in the air in the best 
 way by the use of aeroplanes. 
 
 It was stated on page 129 that further consideration 
 would be given to the assumption that we are within 
 the limits of exactness when we assume the average 
 pressure on the whole plane to be the same as the 
 pressure at the centre. This was correct in that in- 
 stance, but is not to be taken as a general rule. With 
 reference to this, we learn from the observations of 
 Lauriol * that the pressure on each unit of the ae'ro- 
 
 * Revue de rAeronaute, fourth year. 
 
140 AfiRIAL NAVIGATION. 
 
 plane is indeed proportionate to the square of the 
 velocity of movement, but is not dependent on the ve- 
 locity of movement of neighbouring points. Also with 
 the self-registering apparatus for the resultant and com- 
 ponent forces, we must consider not only the forces 
 exerted on the plane, but also its momentum with 
 reference to the centre of the lever. This indicates the 
 points which are moved at the greatest speed, also at 
 the greatest distance from the lever, so that the pressure 
 and the distance, or the two factors of the moment, 
 decrease simultaneously. The deviations that can re- 
 sult from this are, however, in the apparatus discussed, 
 still within the limit of exactness. 
 
 The circular movement of the apparatus has also 
 the inevitable result of carrying the air with it, espe- 
 cially by the points which, like the aeroplane under 
 trial, stand perpendicular to the line of advance. A 
 body carried in a circular movement at the end of an 
 arm r = 9 M or thirty feet long, at a speed of 20 M or 
 sixty-seven feet per second, is thereby subjected to the 
 effect of a centrifugal force, which, per unit of the 
 
 V 2 400 
 mass, amounts to : -^- = 44, or about 4*5 times, 
 
 the gravity being assumed at 9-8. 
 
 The air will not, however, be exposed to such a 
 great centrifugal force, for it will tend to move in the 
 direction of the radii towards the outer side, which will 
 have the result : 
 
 That the relation between the velocity of the air 
 
EXTRACTS FROM A LATER PAMPHLET. 
 
 and of the plane will be modified in quantity and in 
 direction. The renewing of the air will thus, by the 
 contact with the aeroplane, no longer appear under the 
 same conditions ; and as the pressure on the aeroplanes, 
 according to Laugley, will be controlled by the greater 
 or less renewal of the air, it is to be feared that the 
 value of the pressure may be modified by the addition 
 of the component centrifugal force. 
 
 If, on the other hand, the component centrifugal 
 force be disregarded, then the displacement of the cen- 
 tre of pressure in the planes under trial was not cor- 
 rectly indicated, and before determining the power the 
 self-registering moments of the arm of the lever should 
 have been carefully studied. Here the question comes 
 up as to whether or not these forces may be entirely dis- 
 regarded, as they cannot yet be determined. This calls 
 still for an exact comparison with the results that may 
 be reached by velocities in rectilinear movement, and 
 this, for a speed of twenty metres per second (forty- 
 four miles per hour), is only possible by observations to 
 be taken on a railway car, which would even then call 
 for the most careful consideration, and which could 
 probably be carried out under favourable conditions on 
 the Netherlands Railway. 
 
 Lauriol also considers Langley optimistic in his views 
 when he decides that one horse power is sufficient for 
 moving a weight of more than ninety kilogrammes 
 (one hundred and ninety-seven pounds) at a velocity 
 of twenty metres per second. Very possibly there may 
 
142 
 
 AfiRIAL NAVIGATION. 
 
 be more or less justice in this, but an increase of the 
 power of machinery need create no preponderating dif- 
 ficulty, and concerning this further investigations are 
 necessary to a final conclusion. The importance of 
 direct observations at high velocities and on a straight 
 course is, in my opinion, imperative. 
 
 Finally, Drzwiecki, who has already been mentioned 
 in my first publication, compares the results of his ear- 
 lier theoretical observations and computations with the 
 practical investigations of Prof. Langley.* 
 
 
 V. 
 
 a. 
 
 P. 
 
 R. 
 
 Langley, experimentally. . 
 Drzwiecki, by computation 
 
 20m. 
 20m. 
 
 2 
 1 50' 45" 
 
 5-38 kilos. 
 5-17 " 
 
 20 grms. 
 21-7 " 
 
 [The author, referring to the prize papers published 
 in the Cosmopolitan Magazine, by Hiram S. Maxim and 
 John P. Holland, says :] Translator. 
 
 Mr. Maxim is, according to Prof Langley, recog- 
 nized as one who has already distinguished himself by 
 the practical application of his ideas. The apparatus 
 projected by him is now probably complete. It is made 
 on the principle of the aeroplane, with a width of about 
 one hundred feet measured between the extremities of 
 the wings, forming practically stiff, kite-shaped support- 
 ing planes. The machine is provided with two equal 
 screw propellers, comparable with those of the great 
 transatlantic steamers, operated by steam engines of 
 
 * Revue de /' 'Aeronaute, fourth year. 
 
EXTRACTS FROM A LATER PAMPHLET. 143 
 
 about the same nominal horse power as those of the 
 earliest steamers. This power is, according to Lang- 
 ley, probably sufficient for maintaining the horizontal 
 soaring movement of the machine, if only it can be 
 moved in the right direction. 
 
 Especially must the machine be put together in the 
 stoutest manner and constructed with the greatest me- 
 chanical skill. In view of Mr. Maxim's great energy 
 and determination and of his knowledge, we may trust 
 that he will be able to make head against the remaining 
 mechanical difficulties of aerial navigation. This will 
 now be the hearty wish of all ; yet it cannot be con- 
 cealed that he is sure to meet with great difficulties in 
 connection with the steering of his apparatus ; and these 
 must be overcome during its free flight in the air. 
 
 On the other hand, it is not to be denied that in the 
 high velocity of movement that must be attained there 
 exists a guarantee that success will be reached in this 
 also, as may be observed in the case of the movements 
 of bird flight. We can therefore await with confidence 
 the final success of aerial navigation. Nevertheless, he 
 who shall first trust himself to such a means of trans- 
 portation, and take the risk of flying through the ele- 
 ment that lies above us at an amazing speed, must dis- 
 play a dauntless heart and great presence of mind. If 
 he succeeds, however, which in the end cannot be ques- 
 tioned, then there can be no limit to the renown he will 
 reap. 
 
 It must, however, be borne in mind that it is not 
 enough to secure the means for sailing through the air ; 
 we must also learn to make use of these means. In this 
 aspect a comparison may be made with swimming, skat- 
 ing, and riding the bicycle, for which we have the means 
 and the strength, but for which we have to learn the 
 
AfiRIAL NAVIGATION. 
 
 method of application. Probably here, as with every- 
 thing else, it will be the first step that costs, and it is to 
 be expected that the first navigation of the air will be 
 attended with risk of life. Still, this should be no insur- 
 mountable obstacle, for the first balloon ascensions were 
 not without danger, and they were made nevertheless. 
 What yet remains to be assured before aerial navigation 
 can become practicable, as was the case in ordinary navi- 
 gation, is the ability to steer the apparatus, and concern- 
 ing this we are not as yet in a position to form any defi- 
 nite conclusion. 
 
 As supplementing the author's remarks, it will be of 
 interest to refer to the admirable article in the Cosmo- 
 politan Magazine for June, 1892, for which Mr. Maxim 
 received the first prize offered by that magazine. It is 
 here suggested that the trial machine be constructed in 
 a large building, for protection against wind, and that 
 a circular railroad be provided, one mile in circumfer- 
 ence, the machine being mounted on wheels. The con- 
 clusion of the paper is as follows : 
 
 " We should first ascertain how much power was re- 
 quired to propel its bare poles or tubes through the air 
 at various velocities. The machine should be run 
 around the one- mile track at all speeds from twenty 
 miles per hour to one hundred miles per hour, and the 
 power actually required should be carefully noted. 
 These runs would enable us to ascertain how our pumps 
 worked at high speed, and how much our screws pushed, 
 and if we put a brake to the wheels we should find out 
 the slip of the screws. We could also ascertain the effi- 
 ciency of our condenser at various speeds, and the tern- 
 
EXTRACTS FROM A LATER PAMPHLET. 
 
 perature of the water could be taken. In order to run 
 on a railway track, the machine, of course, must be pro- 
 vided with wheels, and two sets of these would be neces- 
 sary ; one set should be of great weight, so as to hold 
 the machine down when running on the track, and the 
 other set should be very light, for actual flying. Springs 
 should be interposed between the axletrees and the ma- 
 chine, after the manner of railway carriages, and there 
 should be attached above each wheel some sort of an in- 
 dex or indicator to show the exact load resting on each 
 wheel. When all the parts of the machine had been 
 made to operate smoothly and satisfactorily, the silk 
 could be placed on the aeroplanes, and then our serious 
 experiments might be said to commence. We should 
 first begin by running slowly say at the rate of twenty 
 miles per hour and carefully note the lift on the in- 
 dexes over each wheel. If we found that with a speed 
 of twenty miles an hour three fourths of the load was 
 lifted off the forward axletree and only one fourth off 
 the hind one, then we should change the centre of 
 weight farther forward so as to bring it as near as pos- 
 sible under the centre of effort or lift. We should then 
 make another trial, and if we found that the lift was 
 equal both fore and aft, we should increase the speed 
 very carefully gradually observing the lift at the four 
 corners of the machine until the whole weight of the 
 machine was supported by the aeroplane, and the whole 
 weight of the wheels about one ton by the railway 
 track. Then, when there was neither lift nor load on 
 either wheel, we might consider that we had arrived at 
 a stage in our experiments where we could turn our at- 
 tention to the subject of steering. 
 
 "A boat has to be steered in only one direction 
 namely, a horizontal direction to the right or to the 
 
146 AERIAL NAVIGATION. 
 
 left. A locomotive torpedo or a flying machine must be 
 steered in two directions, right or left and up or down. 
 We should experiment with the more difficult one at 
 first, namely, the up-and-down or vertical direction. We 
 should attach two long arms to our aeroplane in such a 
 manner that they would project a considerable distance 
 in the rear of the machine. To these arms we should 
 pivot a very large and light silk-covered rudder and 
 connect it with ropes so that it could be turned up or 
 down by a small windlass from the machine. We should 
 then take a run on the track and see if changing the 
 angle of this rudder would increase or diminish the load 
 on the forward or hind wheels. If we found that it 
 would do this, but not sufficiently so, we should attach 
 another rudder in exactly the same manner to the for- 
 ward end of the machine. Suppose that at a speed of 
 thirty-five miles per hour, with both rudders set at the 
 same angle as the aeroplane, we should find that the 
 whole weight of the machine was carried by the aero- 
 plane, and the whole weight of the wheels (two thousand 
 pounds) by the track ; we could then consider that the 
 adjustment of our load was correct, and that the centre 
 of weight was directly under the centre of effort for a 
 speed of thirty-five miles an hour. We should then ele- 
 vate the front edge of the forward rudder and depress 
 the front edge of the rear rudder ; this would cause the 
 machine to lift on the forward axletree and the rear end 
 of the machine to press on the hind axletree. If we 
 found by changing the angle of the rudders that the 
 load could be increased or diminished on either axletree 
 to the extent of fifteen per cent of our whole load, we could 
 consider that this phase of the problem was solved. 
 
 " For horizontal steering, we should try first the effect 
 of the screws. There should be a three-way valve in the 
 
EXTRACTS FROM A LATER PAMPHLET. 147 
 
 steam pipe connected with a lever, so that we should be 
 able to partly close off the steam from the engine of one 
 screw and turn more steam on to the other. This would 
 probably be all that would be found necessary ; if not, 
 we should try rudders. 
 
 " To prevent the machine from swaying in the air, 
 the aeroplane should be so constructed that no matter in 
 which direction it tilted it would diminish the lifting 
 power of the lifted part and increase the lifting power 
 of the depressed part. This would be simple and auto- 
 matic ; moreover, the stability of the machine could be 
 still further increased by having the centre of gravity 
 much below the centre of lift. Having all things in 
 readiness, the heavy wheels should be removed and the 
 light ones put on, and taking one man with us to attend 
 to the two horizontal rudders and to keep the machine 
 on an even keel, we should take our first fly, running 
 the engines and doing the right and left steering our- 
 selves. A day should be selected when there was a fresh 
 breeze of about ten miles per hour. We should first 
 travel slowly around the circular railway until we came 
 near that part of the track in which we should face the 
 wind. The speed should then be increased until it at- 
 tained a velocity of thirty-eight to forty miles an hour. 
 This would lift the machine off the track, and probably 
 would slightly change the centre of effort. This, how- 
 ever, would be quickly corrected by the man at the 
 wheel. While the machine was still in the air careful 
 experiments should be tried in regard to the action of 
 the rudders ; it should be ascertained to what degree 
 they had to be tilted in order to produce the desired ef- 
 fect on the machine. The machine should also be run 
 at a speed less than thirty-five miles per hour in order 
 to allow it to approach the earth gradually ; then the 
 
148 AfiRIAL NAVIGATION. 
 
 speed should be increased again to more than thirty-five 
 miles an hour in order to rise, at the same time trying 
 the effect of running one propeller faster than the other 
 to ascertain to what extent this would have to be done 
 in order to cause the machine to turn to the right or to 
 the left. If the machine should be constructed so that 
 each particular foot of its surface carried a load of one 
 pound two ounces, and if we should stop the engine 
 dead and allow the machine to fall, it would approach 
 the earth at a speed of fifteen miles an hour, or one mile 
 in four minutes. This evidently would cause a consid- 
 erable shock, and unless there was a good deal of elas- 
 ticity to the parts and a good deal of travel between the 
 axletrees and the machine, the shock would probably be 
 sufficient to distort or injure some part of the light 
 structure. But it is not necessary to approach the earth 
 directly. Prof. Langley found in his experiments that 
 when a horizontal plane was travelling rapidly through 
 the air it approached the earth as though it were ' set- 
 tling through jelly.' 
 
 " A large field as near our railway as possible should 
 be selected for alighting, and having approached the 
 field so as to be facing the wind, we should gradually 
 descend by slowing up the engines, and finally alight 
 while the machine was still advancing at the rate of 
 twenty miles an hour. If the wind should be blowing 
 at the rate of ten miles an hour the machine would ap- 
 proach the earth very gradually indeed, so that all shock 
 would be avoided. It would only require a few yards of 
 comparatively smooth ground to run on after alighting 
 in order that there should be no disagreeable shock or 
 danger. The cost of these experiments would be from 
 fifty thousand to one hundred thousand dollars, and the 
 time required would be two years." 
 
EXTRACTS FROM A LATER PAMPHLET. 149 
 
 The author continues : 
 
 Mr. John P. Holland, to whom was awarded the 
 second prize offered by the Cosmopolitan, agrees with 
 Maxim that the navigation of the air appears to be pos- 
 sible only with the use of the aeroplane, and that noth- 
 ing is required for it that is not already known and 
 proved. There is wanting only a suitable apparatus, 
 combining what is now in daily use, and satisfying the 
 following requirements : 
 
 1. The machine must be able to lift and support 
 itself in the air. 
 
 2. It must be capable of rising and alighting ver- 
 tically, and slowly or rapidly at will, in storm or 
 calm. 
 
 3. It must be incapable of tipping over or up- 
 setting. 
 
 4. It must be capable of rapid horizontal motion, 
 and of easy and steady steering in any direction. 
 
 5. The complete machine and each of its parts must 
 be so strong that there would be required to destroy it 
 a strain or stress six to ten times greater than any to 
 which it is ever likely to be subjected. 
 
 The motor must, therefore, be strong and light. It 
 must be ample to lift its own weight and that of the 
 machine with its ballast, and to move it steadily 
 through the air. Mr. Holland is of the opinion that 
 these requirements can be fully met by the use of the 
 screw propeller and the aeroplane. 
 
 Agreeing with his opinion, I found it the more 
 
150 AfiRIAL NAVIGATION. 
 
 entitled to acceptance because he has already distin- 
 guished himself as a constructor by the building of a 
 submarine boat or torpedo, and he chooses this as the 
 example best to be followed in navigating the air. 
 This did not surprise me, for I had already (Chap- 
 ter III) pointed out the similarity of air balloons with 
 sea and river buoys; but the comparison of the torpedo 
 with devices for traversing the air seems to me much 
 closer. Both must always move with great speed 
 through the surrounding fluid, the first through the 
 water and the second through the air, and each must 
 find support in its medium in order to maintain its 
 stability and to travel. Both also have a tendency to 
 sink or fall in the fluid, which, however, must not be 
 permitted, so that they must not exceed a certain 
 weight relatively to the resistance of the medium in 
 which they are immersed. There thus exists, as to the 
 motive power and the required lightness, an undoubted 
 similarity in the conditions that must serve for the tor- 
 pedo and for the air machine, and this justifies Mr. 
 Holland's preference. 
 
 We can also point to a considerable number of pow- 
 erful and at the same time light motors, used in con- 
 nection with torpedo boats, which, including boiler and 
 fuel, weigh only sixty pounds per horse power. In this 
 matter attention may also be called to the following : 
 
 Mr. Norman L. Munro's yacht Norwood had boilers 
 and engines weighing only nineteen pounds per horse 
 power. 
 
EXTRACTS FROM A LATER PAMPHLET. 151 
 
 Mr. H. S. Maxim has built and operated a boiler 
 and engines that weigh together only nine pounds per 
 horse power. 
 
 Mr. Stringfellow, of London, built a complete steam 
 motor, nearly a quarter of a century ago, that weighed 
 only thirteen pounds per horse power. Prof. Langley 
 is authority for the statement that effective steam en- 
 gines have lately been built weighing less than ten 
 pounds per horse power. 
 
 It is further to be said that 
 
 Freninges, of Copenhagen, obtained by the lift of 
 his wheel the effect of sixty-three per cent of the power 
 applied. 
 
 Langley, in his observations, obtained a lifting effect 
 of two hundred and forty pounds per horse power. 
 Maxim obtained similar results. 
 
 These machines are all light enough, and even the 
 heaviest that of the torpedo, weighing sixty pounds 
 per horse power has a not inconsiderable margin, for, 
 with a useful effect of sixty-three per cent and a weight 
 
 of sixty pounds, about ^ = 95 pounds per horse 
 
 DO 
 
 power will be delivered. Making the usual deduction 
 for loss and friction, we get a weight of less than one 
 half of what one horse power can lift. 
 
 Meanwhile Mr. Holland considers fourteen pounds 
 per horse power enough for the weight of the rest of 
 the machine, giving a total weight of 95 -j- 14 = 109 
 pounds per horse power, leaving a margin of 240 109 
 
152 AERIAL NAVIGATION. 
 
 = 131 pounds per horse power before reaching the 
 limit of the lifting force. 
 
 He then considers whether or not the Norwood 
 boilers and engines will meet the conditions set up. 
 He supposes a pair of propeller wheels of suitable di- 
 mensions to be placed in a framework concentrically or 
 on concentric shafts with the Norwood boiler and en- 
 gine, as shown in the figure. Care must be taken so to 
 place the machinery that its centre of gravity falls in or 
 under the propeller shafts. 
 
 FIG. 14. Scale, one-sixteenth inch^l foot. 
 
 The apparatus will rise when the upward thrust 
 caused by the revolution of the propellers is greater 
 than the weight of the machine. The maximum speed 
 of ascent will depend on the amount of reserve lifting 
 power. This, arid the speed of descent, may be regu- 
 lated by the throttle- valve. 
 
 The machine answers in this condition for- higher 
 requirements than a balloon, because it completely satis- 
 fies conditions 1, 2, and 3, and, besides, a motor can be 
 
EXTRACTS FROM A LATER PAMPHLET. 153 
 
 made light and strong enough to meet the require- 
 ments of the 5th condition. There remains, then, only 
 the 4th condition of rapid horizontal propulsion, which, 
 as Holland shows, may be attained without providing 
 any special power for the purpose. For this, aeroplanes 
 are employed, and modifying the design, as shown in 
 Figs. 15, 16 and 17, to permit of inclining the axes of 
 the screws to a horizontal position, the power may be 
 applied directly to lifting at first, and, when a suitable 
 elevation has been attained, the axes of the screws, with 
 the engines and framework, may be revolved about their 
 common centre of gravity through ninety degrees, so 
 that the axes or the common axis is placed horizontally. 
 
 While the machine is rising vertically, the power 
 exerted by the screws serves both to support its weight 
 and for the upward movement. When the axis is in- 
 clined, by the revolving of the framework, the power is 
 in part transferred to the production of a horizontal 
 movement, and in part to the support of the machine, 
 in connection with the soaring of the aeroplanes. The 
 operation is reversed in descending. We have then 
 only to regulate the inclination of the axis, according to 
 the direction and force of the wind, to make vertical 
 descent possible even during a storm. 
 
 Thus the 2d, and the first part of the 4th condition, 
 will be satisfied, while for the second part of the 4th 
 there will be needed only vertical and horizontal rud- 
 ders, after the manner of submarine boats and White- 
 head torpedoes. 
 11 
 
154 AfiRIAL NAVIGATION. 
 
 The superficial extent of aeroplanes is fixed by 
 Chanute's table, which gives more than is needed, as it 
 is based on experiments with flat planes of considerable 
 thickness and with rectangular edges. We should, 
 therefore, get better results with modified forms and 
 sharpened edges. This is indicated by the important 
 experiments of Horatio Phillips, of London, in 1885, 
 where ordinary planes were compared with a thin plane 
 with sharp edges, concave on the under and convex on 
 the upper side. These experiments were confined to 
 angles of fifteen degrees with the horizon, yet their re- 
 sults were remarkable. They should be more decisively 
 repeated with Prof. Langley's apparatus. 
 
 FIG. 15. ELEVATION. 
 
 At an angle of fifteen degrees with the horizon, a 
 thin flat plane had a power for lifting, according to 
 Phillips, of 4-5 and, according to Chanute, of 3-714 
 times that of horizontal movement. The effect of the 
 thickness of the edges in Chanute's tables is, however, 
 uncertain, but, to judge from the correspondence of his 
 results with those of Langley, there must have been a 
 great similarity between the planes used in the experi- 
 ments. 
 
 The results obtained by Phillips were sixteen per 
 
EXTRACTS FROM A LATER PAMPHLET. 155 
 
 cent more favorable than Chanute's, which probably 
 resulted from the finer edges of the planes, and by the 
 form. The results ought, however, to have been still 
 more favorable, if the planes had been concave in the 
 line of the direction of the wind and convex at the 
 back, with stream lines at the edges. A plane of this 
 sort, moderately concaved, but quite thick toward the 
 leading edge, gave a force in lifting of 10-34 times that 
 of the horizontal movement. This result seems, there- 
 fore, to be 2-75 times better than that of the angular 
 plane and 2 -3 times better than by Phillips's experi- 
 ments. If these last are trustworthy, we need use only 
 three hundred and sixty-five square feet of aeroplane 
 where Chanute's table indicates one thousand square 
 feet. The smaller dimensions are shown in the sketch, 
 Eig. 17. 
 
 It is, however, quite possible that the superiority of 
 the smaller planes tried by Phillips will appear less with 
 smaller angles of elevation, though Holland suggests 
 that it will continue for the smallest angles practical 
 with aeroplanes. It appears also that the shapes of 
 their sections modify the stream lines, reducing the 
 horizontal resistance without changing the lift. This 
 makes a greater angle of inclination possible, and ob- 
 viates the liability to vibration that Maxim observed 
 with very small angles, giving the power of a large 
 surface at slight inclination, without its disadvantages. 
 
 Remembering that observation has shown the sur- 
 face of the aeroplane, for a certain weight, to be in- 
 
156 AERIAL NAVIGATION. 
 
 versely as the square of the velocity, and that the lift- 
 ing power and the horizontal force increased directly as 
 the square of the velocity, it is further possible that we 
 may attain great speed with a very compact machine ; 
 but this opinion can lead to no practical results until it 
 is established by more extended suitable experiment. 
 
 FIG. 16. END VIEW. 
 
 Chanute's table shows also that for a good weight 
 and great speed a small angle of inclination will suffice. 
 One square foot of aeroplane, at an inclination of four 
 degrees with the horizon, will, with a velocity of eighty 
 miles per hour, give 4-448 pounds lift and a horizontal 
 resistance of 0-3104 pound; so this aeroplane must be 
 moved 7,040 feet per minute against a resistance of 
 0-3104 pound, amounting to 2,185-216 foot-pounds per 
 minute, which is equal to 0-0662 horse power per square 
 foot of aeroplane. Using the Norwood engines, with 
 four hundred indicated horse power, we get a useful ef- 
 fect of sixty-five per cent less than with some torpedo 
 boats and we have 400 X "65 = 260 horse power avail- 
 able, and for the surface of the aeroplane, according to 
 
 9RO 
 
 Chanute, - =3,928 square feet of aeroplane surface; 
 
 3,928 X 4-448 = 17,471 total lifting power. 
 
 Holland further estimates the weight of the com- 
 
EXTRACTS FROM A LATER PAMPHLET. 157 
 
 plete machine, including engines, with all appliances 
 and operators, as twenty-nine pounds per indicated 
 horse power. 
 Total weight (400 horse power X 29 pounds) 11,600 pounds. 
 
 Total lifting power 17,471 " 
 
 Reserve lifting power 5,871 " 
 
 The correct adjustment of length to breadth of the 
 calculated aeroplane is very important. That this is by 
 no means a matter of indifference appears in a general 
 way: 
 
 1. From the observations of Froude, with regard to 
 frictional resistance of flowing water, which, with planes 
 of equal area, increased with the increase of the width 
 across the stream and with the decrease of length in the 
 direction of the stream ; and 
 
 2. From the observations of Prof. Langley, who de- 
 duced the same results for resistance in the air. 
 
 We are, however, wandering in complete uncertainty 
 as to the value to be ascribed to the different measure- 
 ments, if we consider a large continuous surface, espe- 
 cially if it is capable of concaving, with an increase of 
 efficiency, as is indicated by sailing vessels. We can thus 
 make no calculation as to whether this advantage equals 
 or overbalances that of the narrow planes or not. A 
 single great plane will be simpler and lighter than a 
 great number of small planes. On the other hand, from 
 the point of view of safety, this would seem to offer less 
 liability to accident, as will be seen by a comparison of 
 Figs. 15, 16, 18, and 19. 
 
158 
 
 AERIAL NAVIGATION. 
 

 EXTRACTS FROM A LATER PAMPHLET. 159 
 
 According to Chanute, the flying machine has to 
 encounter three elements of resistance due to the 
 weight of the apparatus, to the velocity of movement, 
 and to the friction on the surface (skin friction). 
 
 According, however, to the observations of Langley 
 and Phillips, the loss of power by the skin friction and 
 by the slip is included in the propelling power, so that, 
 speaking in general terms, we need take account only of 
 the velocity. 
 
 Mr. Holland has deduced his pair of screw propellers 
 from the observations of Dr. Freninges. They must be 
 able, with four hundred revolutions per second, to lift 
 together a weight of 17,471 pounds. Their diameters 
 are fixed at 16*89 feet and 14-16 feet, which at the same 
 speed will give them equal power, and, of this, sixty- three 
 per cent is assumed to be available. 
 
 The axes of the propellers in rising are placed ex- 
 actly over and eight feet above the centre of gravity. 
 For horizontal movement they are in the plane of the 
 centre of resistance and five feet above the centre of 
 gravity. 
 
 The weight of the motor and gearing is fixed as per 
 the statements given : 
 
 Weight of Motor and Gear. 
 
 Boiler, complete, with water 4,000 pounds. 
 
 Engines, propellers, and frame . . . 2,000 " 
 
 Total weight of motor 6,000 " 
 
160 AfiRIAL NAVIGATION. 
 
 Weight of motor and gear per indicated horse power, 
 
 6,000 -T- 400 = 15 pounds per horse power. 
 Weight of body, aeroplanes, connections, and oper- 
 ators : 
 
 Aeroplane frame 1,800 pounds. 
 
 Body 900 " 
 
 Cover for both 1,176 " 
 
 Trussing, stays, and braces 200 " 
 
 Three men . 450 " 
 
 4,526 " 
 Weight of machine and operators per indicated horse 
 
 power, 
 
 4,526 -T- 400 = 11-31 pounds. 
 
 Weight of machine and motor, complete, with oper- 
 ators, per indicated horse power, 
 
 10,526 -^ 400 = 26-31 pounds per horse power. 
 
 Carrying Power. 
 
 Total lifting power at 80-miles speed . . . 17,471 pounds. 
 Total weight, complete, but unloaded . . . 10,526 " 
 
 Carrying power 6,945 " * 
 
 As to the accidents and difficulties which may be 
 encountered, Holland says that, in view of the rapidity 
 of horizontal movement, a comparison with railroad 
 travel is suggested. In this comparison aerial naviga- 
 tion is distinguished from railroad travel by an extraor- 
 dinary smoothness of movement and the absence of many 
 
 * Cosmopolitan Magazine for November, 1892, p. 94. 
 
EXTRACTS FROM A LATER PAMPHLET. 161 
 
 difficulties with which, railroad men have to contend, 
 such as irregularities in the roadbed due to the slightest 
 settlement, the joints of the rails, curves, vibration of the 
 track, drawbridges, etc. Then, too, no care need be 
 given to the correct position of signals, and there is 
 nothing to be feared from obstructions by snow, freight 
 trains, etc. 
 
 As to the possibility that the machine may not always 
 maintain its position in the air, this cannot be altogether 
 denied, even with the greatest care devoted to the plan- 
 ning and execution of the apparatus. Should, however, 
 such trouble unexpectedly arise in the air, the vehicle 
 still cannot suddenly come to a standstill and fall at 
 once. It will, on the contrary, continue until its mo- 
 mentum is exhausted, and the descent can without dif- 
 ficulty be so controlled as to alight on a smooth place, 
 with little speed and without shock or injury. This 
 seems to be the opinion of Mr. Maxim, as well as of 
 Mr. Holland. Even when alighting in the water there 
 would not be a particle of immediate danger, for no 
 shock would be felt, and the machine would float like 
 an ordinary boat. If the injury is slight and can be 
 quickly repaired, the machine can rise from the water 
 and continue its flight. 
 
 The framework and the propellers can be made 
 strong enough for all contingencies. 
 
 If we examine the relative positions of the point 
 upon which the propelling power acts, and of the cen- 
 tres of resistance, of support and of gravity, during hori- 
 
162 
 
 AERIAL NAVIGATION. 
 
 zontal movement and during ascent and descent, we 
 must see that the machine cannot capsize, for the laws 
 of Nature will prevent it. 
 
 Such difficulties as may be apprehended have indeed 
 all been met and overcome in submerged vessels and 
 
 FIG. 18. DESIGN WITH SUPERPOSED AEROPLANE. 
 Scale one-sixteenth inch=l foot. 
 
 torpedoes. They are evidently the same in this case, 
 and they can be prevented by the same means, includ- 
 ing the use of rudders of small size. 
 
 Finally, taking the estimates made as a basis, we 
 must calculate on a considerable addition to our reserve 
 force, to provide against unforeseen conditions and to 
 enable us to make subsequent improvements. 
 
 A thoughtful consideration of the projects and ideas 
 of Mr. Holland cannot fail to lead to the conviction 
 that the possibility of navigating the air is no longer to 
 be disputed on theoretical grounds. On the practical 
 side we have still to consider 
 
 1. In how far the velocities and the phenomena at- 
 
EXTRACTS FROM A LATER PAMPHLET. 163 
 
 tending circular movement will correspond with those 
 of rectilinear movement. 
 
 2. Whether or not an apparatus constructed of alu- 
 minum, for the sake of lightness, will be in all respects 
 strong enough. Possibly experience with the torpedo 
 boats has given some indications as to this. 
 
 3. What is the best form for aeroplanes, and what 
 is the minimum speed required at low angles of inclina- 
 tion, in order to carry a given weight of apparatus and 
 load with the necessary stability in the air ? 
 
 4. How steering at high velocities is to be insured. 
 This may not be easy to do, and the difficulty may turn 
 out to be only a temporary one. 
 
 5. What would be the influence of barometric con- 
 ditions and the greater or less rarity of the air on its 
 resisting power for the propulsion of the machine? 
 The table on page 29, and the observations made in 
 Chapter III, should be consulted for an assurance as to 
 this influence. 
 
 It cannot be doubted that a scientific shipbuilder, 
 possessing the required theoretical knowledge, will be 
 able, following these principles, to plan an apparatus 
 for navigating the air and to construct it and put it in 
 operation. Such a machine could, perhaps, lay no 
 claim to the best solution of the question, nor to cor- 
 rect proportion of its details, but that was also the 
 case in the past with ordinary navigation. It is more 
 to be expected here, because the investigations re- 
 quired for aerial navigation are not yet completed, 
 
164 
 
 AfiRIAL NAVIGATION. 
 
EXTRACTS FROM A LATER PAMPHLET. 165 
 
166 AERIAL NAVIGATION. 
 
 as is plain from the preceding considerations of the 
 subject. 
 
 Knowledge is power, and it is most desirable that 
 the whole subject be earnestly studied, so that the gaps 
 still remaining may be filled. The development of 
 aerial navigation was checked for nearly a century by 
 the lack of knowledge to be gained only by thorough 
 investigation. Scientific investigation really began only 
 in the second half of this century, and it seems to me 
 that in this field the installation at Chalons and the 
 experiments of Prof. Langley are distinguished above 
 all else. Some delay is to be expected. The necessary 
 observations must require much time in my opinion 
 three years, if not longer and the World's Fair at 
 Chicago will not see them completed. It will, on the 
 other hand, stimulate public interest to see aerial navi- 
 gation practically exhibited there, even though not 
 completely successful, as is, of course, to be expected. 
 
 This wonderful nineteenth century may yet show, as 
 its final great achievement, a thus far unexpected per- 
 fection of the balloon, and, what will be still more im- 
 portant, a successful application of Nadar's principle, 
 "Leplus lourd que Pair" 
 
 This may exert a powerful influence on social con- 
 ditions, of which we can now form no adequate idea. 
 
 ARCACHON, February, 1893. 
 
PROF. LANGLEY'S EXPERIMENTS* 
 
 No account of what has been done in connection 
 with the navigation of the air would be complete, if 
 even fully comprehensible, without further reference to 
 the remarkable experiments in the field of aerodynam- 
 ics devised and carried out by Prof. Langley. These 
 are fully set forth in Volume XXVII of the Smithso- 
 nian Contributions to Knowledge. It will be useful to 
 reproduce here some of the less detailed portions of 
 Prof. Langley's report. He says : 
 
 "To prevent misapprehension, let me state at the 
 outset that I do not undertake to explain any art of 
 mechanical flight, but to demonstrate experimentally 
 certain propositions in aerodynamics which prove that 
 such flight under proper direction is practicable. This 
 being understood, I may state that these researches have 
 led to the result that mechanical sustentation of heavy 
 bodies in the air, combined with very great speeds, is 
 not only possible, but within the reach of mechanical 
 means we actually possess; and that while these re- 
 searches are, as I have said, not meant to demonstrate 
 the art of guiding such heavy bodies in flight, they do 
 
 * Experiments in Aerodynamics, by S. P. Longley, Smithso- 
 nian Institution, Washington, 1891. 
 
168 AERIAL NAVIGATION. 
 
 show that we now have the power to sustain and propel 
 them. 
 
 " Further than this, these new experiments (and the- 
 ory also, when reviewed in their light) show that if in 
 such aerial motion there be given a plane of fixed size 
 and weight, inclined at such an angle, and moved forward 
 at such a speed that it shall be sustained in horizontal 
 flight, then the more rapid the motion is the less will 
 be the power required to support and advance it. This 
 statement may, I am aware, present an appearance so 
 paradoxical that the reader may ask himself if he has 
 rightly understood it. To make the meaning quite in- 
 dubitable, let me repeat it in another form, and say that 
 these experiments show that a definite amount of power 
 so expended at any constant rate, will attain more eco- 
 nomical results at high speeds than at low speed e. g., 
 one horse power thus employed will transport a larger 
 weight at twenty miles an hour than at ten, a still larger 
 at forty miles than at twenty, and soon, with an increas- 
 ing economy of power with each higher speed, up to 
 some remote limit not yet attained in experiment, but 
 probably represented by higher speeds than have as yet 
 been reached in any other mode of transport a state- 
 ment which demands and will receive the amplest con- 
 firmation later in these pages. 
 
 "In this untrodden field of research, which looks to 
 mechanical flight not by means of balloons but by 
 bodies specifically heavier than the air in which they 
 move, I think it safe to say that we are still, at the time 
 this is written, in a relatively less advanced condition 
 than the study of steam was before the time of Newco- 
 men ; and if we remember that such statements as have 
 been commonly made with reference to this, till lately 
 
PROF. LANGLEY'S EXPERIMENTS. 169 
 
 are, with rare exceptions, the product of conjecture 
 rather than of study and experiment, we may better see 
 that there is here as yet no rule to distinguish the 
 probably important from the probably unimportant, 
 such as we command in publications devoted to the 
 progress of already established sciences. 
 
 " I do not, then, offer here a treatise on aerodynam- 
 ics, but an experimental demonstration that we already 
 possess in the steam engine as now constructed, or in 
 other heat engines, more than the requisite power to 
 urge a system of rigid planes through the air at a great 
 velocity, making them not only self-sustaining, but 
 capable of carrying other than their own weight. This 
 is not asserting that they can be steadily and securely 
 guided through the air, or safely brought to the ground 
 without shock, or even that the plane itself is the best 
 form of surface for support ; all these are practical con- 
 siderations of quite another order, belonging to the yet 
 inchoate art of constructing suitable mechanisms for 
 guiding heavy bodies through the air on the principles 
 indicated, and which art (to refer to it by some title 
 distinct from any associated with ballooning) I will 
 provisionally call aerodromics* With respect to this 
 inchoate art, I desire to be understood as not here offer- 
 ing any direct evidence, or expressing any opinion other 
 than may be implied in the very description of these 
 experiments themselves." 
 
 There was used in these experiments w r hat was called 
 a " whirling-table " a revolving arm, sixty feet long, 
 
 * From acpoSpo/jiew, to traverse the air ; aepofy6fws, an air- 
 runner. 
 
 12 
 
170 AfiRIAL NAVIGATION. 
 
 driven by a central axis, geared to a ten-horse-power 
 engine. The plane of revolution was about eight feet 
 above the ground. The highest speed attainable for 
 the end of the arm was about seventy miles per hour. 
 The precise velocity was determined by an electrical 
 self-registering apparatus. 
 
 The aeroplanes used in the experiments were mount- 
 ed at the end of one of the arms in such a way as to 
 reduce resistances due to centrifugal force and to fric- 
 tion to a minimum, and these resistances were carefully 
 measured by suitable appliances. Other devices were 
 used for recording the resultant pressure, the compo- 
 nent pressure, the velocity of fall of the plane at rest 
 and in motion, and the time-power consumed. 
 
 " Perhaps the most important primary fact exhibited 
 by these experiments is that the time of fall for hori- 
 zontal planes of all shapes is greater as the horizontal 
 velocity increases, and also (as the form of the curves 
 shows) that this retardation in the velocity of falling 
 goes on at an increasing rate with increasing velocities 
 of translation. 
 
 "Secondly, we see that those planes whose width 
 from front to back is small in comparison with the 
 length -of the advancing edge have a greater time of 
 fall than others. This difference is uniform and pro- 
 gressive from the 6 X 12 inch planes to the 18 X 4 
 inch planes. Expressing this advantage quantitatively, 
 the curves show that the planes having an advancing 
 edge of six inches and a width of twelve inches from 
 front to back, when they have a horizontal velocity of 
 twenty metres per second, fall the distance of four feet 
 
PROF. LANGLEY'S EXPERIMENTS. 171 
 
 in - 7 second, while planes of the same area and weight 
 having the advancing edge eighteen inches and four 
 inches from front to back, when moving with the 
 same velocity, are upheld to such an extent that their 
 time of fall is two seconds. This interesting compara- 
 tive result is also indirectly valuable in giving additional 
 evidence that the largely increased time of fall of the 
 better-shaped planes at the high speeds is not due to the 
 lateral friction of the falling piece against the frame. 
 The friction with the 6 X 12 inch planes is as great 
 as with any of the others, yet their time of falling is 
 only slightly greater at high speeds than at rest. At- 
 tention is called to the fact that at the highest velocity 
 attained in the present series of experiments twenty 
 metres per second the curve shows that the time of 
 falling of the 18 X 4 inch planes was increasing very 
 rapidly so much so as to make it a subject of regret 
 that the slipping of belts prevented experiments at still 
 higher speeds. We may, however, reasonably infer that, 
 with a sufficient horizontal velocity, the time of fall may 
 be prolonged to any assigned extent, and that for an 
 infinite velocity of translation the time of fall will be 
 infinite, or, in other words, that the air will act as a 
 solid support. 
 
 " It may be of interest to connect these observations 
 with some partly analogous facts which are more fa- 
 miliar. 
 
 " It is frequently observed that a sheet of very thin 
 ice will bear up a skater, if he is in rapid motion, which 
 would not sustain his weight if he were still ; and even 
 if we neglect the slight difference of specific gravity be- 
 tween water and ice, and suppose the latter to have no 
 differential buoyancy, the rapid skater will still be able 
 to pass safely over ice that would not bear his weight if 
 
172 AERIAL NAVIGATION. 
 
 he were at rest ; for while his mass is the same in hoth 
 cases, that of the ice called into play in sustaining him 
 is only that corresponding to one unit of area when he 
 is at rest, but to many when he is moving. 
 
 " In this form of explanation and illustration the at- 
 tention is directed only to the action of the air beneath 
 the plane, but, in fact, the behaviour of the air above the 
 plane is of perhaps equal importance, and its action has 
 been present to my mind throughout these experiments, 
 although for the purpose of concise exposition only the 
 former is here referred to. By analogous reasoning in 
 the case of a heavy body immersed in any continuous 
 fluid, even gaseous, while the mass of air or gas whose 
 inertia is called into action is small and affords a slight 
 sustaining power when the body is at rest, it becomes 
 greatly multiplied by lateral motion, and the more rapid 
 this lateral motion the greater will be the sustaining 
 action of the fluid. So, then, in the case of any heavy 
 body which will fall rapidly in the air if it fall from rest, 
 the velocity of fall will be more and more slow if the 
 body be given successively increasing velocities of lateral 
 translation and caused to run (so to speak) upon fresh 
 masses of air, resting but a moment upon each. 
 
 " The above analogy, in spite of its inefficiency as re- 
 gards the effect of elasticity, is useful, and may be fur- 
 ther extended to illustrate the relative results obtained 
 with the differently shaped planes and with the same 
 plane under different " aspects " ; thus the action on the 
 air of a plane whose advancing edge is twice its lateral 
 edge e. g., the 12 X 6 inch plane, with twelve-inch side 
 foremost may be compared to that of two skaters side 
 by side, each advancing over his own lines of undis- 
 turbed ice ; but the same plane with the six-inch side 
 foremost, to the same skaters, when one is behind the 
 
PROF. LANGLEY'S EXPERIMENTS. 173 
 
 other, so that the second is passing over ice which has 
 already yielded to the first and is partly sinking. 
 
 " The second series of experiments, made on the same 
 dates as the first, was to cover the third object of ex- 
 periment that is, to determine for different angles of 
 inclination what speed is necessary in order to derive 
 an upward thrust just sufficient for sustaining the 
 planes. 
 
 " The results of these two series of experiments fur- 
 nish all that is needed to completely elucidate the propo- 
 sition that I first illustrated by the suspended plane, 
 namely, that the effort required to support a bird or 
 flying machine in the air is greatest when it is at rest 
 relatively to the air, and diminishes with the horizontal 
 speed which it attains, and to demonstrate and illustrate 
 the truth of the important statement that in actual hori- 
 zontal flight it costs absolutely less power to maintain a 
 high velocity than a low one. It has already been ex- 
 plained that when the planes have such an angle of ele- 
 vation and such a horizontal velocity that they first rise 
 from their support, and are then with a slightly dimin- 
 ished velocity just sustained without falling, they are 
 said to ' soar,' and the corresponding horizontal veloci- 
 ty is called ' soaring speed.' " 
 
 The planes experimented with, described in the 
 previous pages, were set in pairs, and in one set of 
 experiments observations were taken of the effect of 
 placing one above the other at different distances of 
 separation. 
 
 " The results of these observations with two sets of 
 planes, one above the other, give us a first conception 
 of the form and initial vertical amplitude of the wave 
 
174 AERIAL NAVIGATION. 
 
 that is set in motion in the air by a plane passing hori- 
 zontally through it in the manner of these planes. 
 
 " These later observations also furnish incidentally 
 additional data as to the velocity of soaring. When 
 inclined at an angle of ten degrees, the single planes 
 and the double planes, at a distance of four inches apart 
 and upward, are sustained in the air if they have a hori- 
 zontal velocity of about 13*2 metres per second. When 
 set at one degree, soaring took place at velocities from 
 twenty-one to twenty-three metres per second. Close 
 observation also indicated that the error of verticality 
 of the plane-dropper during motion did not exceed one 
 degree ; hence, for these velocities the soaring angle 
 may be taken at about two degrees. . . . 
 
 " The most general and perhaps the most important 
 conclusion to be drawn from them appears to be that 
 the air is sensibly disturbed Bunder the advancing plane 
 for only a very slight depth ; so that for the planes four 
 inches apart, at the average speeds, the stratum of air 
 disturbed during its passage over it is at any rate less 
 than four inches thick. In other words, the plane is 
 sustained by the compression and elasticity of an air 
 layer not deeper than this, which we may treat, for all 
 our present purposes, as resting on a solid support less 
 than four inches below the plane. (The reader is again 
 reminded that this sustenance is also partly due to the 
 action of the air above the plane.) 
 
 " I may add that these experiments with the horizon- 
 tal plane, when properly executed, give results of a char- 
 acter to forcibly impress the spectator ; for, since there is 
 no inclination, there is no visible component of pressure 
 to prolong the fall, yet the plane nevertheless visibly 
 behaves as if nearly deprived of its weight. The pair of 
 
PROF. LANGLEY'S EXPERIMENTS. 175 
 
 18 X 4 inch planes, for instance, one tenth of an 
 inch thick and weighing four hundred and sixty-four 
 grammes, has a specific gravity of about 1,660 times that 
 of air ; yet while the retardation due to the still air in 
 the direct fall is but 8< 03, that due to the same air in 
 strictly lateral motion is 1 8 -50 a most noteworthy result 
 in its bearing on the use in mechanical flight that may 
 be derived from a property of the air much utilized by 
 Nature, but hitherto almost wholly neglected in this con- 
 nection by man its inertia. 
 
 " The experiments consisted in measuring with a dy- 
 namometer the actual resistance to motion experienced 
 by planes when just ' soaring ' or supporting themselves 
 under all the circumstances of flight in free air, except 
 that the plane is restricted from the ' flouncing ' caused by 
 irregular currents, etc., and made to hold a steady flight. 
 
 " The most important conclusion may be said to be 
 the confirmation of the statement that to maintain stick 
 planes in horizontal flight at high speeds less power is 
 needed than for low ones. 
 
 " In this connection I may state the fact, surely of 
 extreme interest in its bearing on the possibility of 
 mechanical flight, that while an engine developing one 
 horse power can, as has been shown, transport over two 
 hundred pounds at the rate of twenty metres per second 
 (forty-five miles an hour), such an engine (i. e., engine 
 and boiler) can be actually built to weigh less than one 
 tenth of this amount." 
 
 Concerning a series of experiments with propellers 
 of various forms, sizes, and materials to determine the 
 ratio of power put out to return in end thrust obtained, 
 Prof. Langley says : 
 
176 AERIAL NAVIGATION. 
 
 " The whole series of experiments is not given here 
 in detail, but their principal results will be communicated 
 in general terms. The first result is that the maximum 
 efficiency of a propeller in air, as well as in water, is ob- 
 tained with a small number of blades. A propeller with 
 two blades gave nearly or quite as good results as one 
 with a greater number. This is strikingly different 
 from the form of the most efficient windmill, and it 
 may be well to call attention to the essential difference 
 in the character of the two instruments, and to the fact 
 that the windmill and the movable propeller are not 
 reversible engines, as they might at first sight seem to 
 be. It is the stationary propeller i. e., the fan-blower 
 which is in reality the reversed windmill ; and of these 
 two the most efficient form for one is essentially the 
 most efficient form for the other. The efficiency of a 
 fan-blower of given radius is expressed in terms of the 
 quantity of air delivered in a unit of time for one unit 
 of power put out ; that of the windmill may be expressed 
 in terms of the amount of work done per unit quantity 
 of air passing within the radius of the arms. If any air 
 passes within the perimeter which does not strike the 
 arms and do its work, it is so much loss of an attainable 
 efficiency. This practical conclusion is confirmed by 
 experience, since modern American windmills, in which 
 practically the entire projection area is covered with the 
 blades, are well known to be more efficient than the old 
 windmills of four arms. 
 
 " Turning now to the propeller, it will be seen that 
 the expression for its efficiency viz., the ratio of useful 
 work done to power expended involves quite different 
 elements. Here the usual work done (in a unit of time) 
 is the product of the resistance encountered by the dis- 
 tance advanced, which is entirely different in character 
 
PROF. LANGLEY'S EXPERIMENTS. 177 
 
 from that in the fan-blower, and almost opposite condi- 
 tions conduce to efficiency. Instead of aiming to set in 
 motion the greatest amount of air, as in the case of the 
 fan-blower, the most efficient propeller is that which sets 
 in motion the least. The difference represents the dif- 
 ference between the screw working in the fluid without 
 moving it at all, as in a solid nut, and actually setting it 
 in motion and driving it backward a difference analo- 
 gous to that which in marine practice is technically 
 called ' slip,' and which is a part of the total loss of 
 efficiency, since the object of the propeller is to drive 
 itself forward and not to drive the air backward. It 
 may now be seen why the propeller with few blades is 
 more efficient than one with many. The numerous 
 blades, following after each other quickly, meet air 
 whose inertia has already yielded to the blades in ad- 
 vance, and hence that does not offer the same resistance 
 as undisturbed air or afford the same forward thrust. 
 In the case of the propeller with two blades, each blade 
 constantly glides upon new strata of air and derives 
 from the inertia of this fresh air the maximum forward 
 thrust. The reader will observe the analogy here to the 
 primary illustration of the single rapid skater upon thin 
 ice, who advances in safety where a line of skaters, one 
 behind the other, would altogether sink, because he 
 utilizes all the sustaining power to be derived from the 
 inertia of the ice and leaves only a sinking foothold for 
 his successors. The analogy is not complete, owing to 
 the actual elasticity of air and for other reasons, but the 
 principle is the same. A second observation relating to 
 aerial propellers, and one nearly related to the first, is 
 that the higher the velocity of advance attained the less 
 is the percentage of ' slip,' and hence the higher the 
 efficiency of the propeller. The propeller of maximum 
 
178 AfiRIAL NAVIGATION. 
 
 efficiency is in theory one that glides through the air 
 like a screw in an unyielding frictionless bearing, and 
 obtains a reaction without setting the air in motion at 
 all. Now, a reaction from the air arising from its in- 
 ertia increases, in some ratio as yet undetermined, with 
 the velocity with which it is struck ; and if the velocity 
 is high enough it is rendered probable, by facts not here 
 recorded, that the reaction of this ordinarily most mobile 
 gas may be practically as great as we please, and, with 
 explosive velocities, for instance, may be as great as 
 would be the reaction of a mass of iron. 
 
 " The theory of aerial propellers being that, for a max- 
 imum efficiency, the higher the velocity the sharper should 
 be the pitch of the blades, it has been the object of the 
 complete series of experiments with the dynamometer- 
 chronograph to determine by actual trial the velocity of 
 advance at which the maximum efficiency is attained 
 when the blades are set at different angles, and the best 
 forms and dimensions of the blades. The details of 
 these are reserved for future publication, but, very gen- 
 erally speaking, it may be said that, notwithstanding the 
 great difference between the character of the media, one 
 being a light and very compressible, the other a dense 
 and very incompressible fluid, these observations have 
 indicated that there is a very considerable analogy be- 
 tween the best form of aerial and of marine propeller. 
 
 " The essential feature of the present work has been 
 the insistence on the importance of a somewhat un- 
 familiar idea that rapid aerial locomotion can be ef- 
 fected by taking advantage of the inertia of the air and 
 its elasticity. Though the fact that the air has inertia 
 is a familiar one, and though the flight of certain mis- 
 siles has indicated that this inertia may be utilized to 
 
PROF. LANG LEY'S EXPERIMENTS. 179 
 
 support bodies in rapid motion, the importance of the 
 deductions to be made has not been recognized. This 
 work makes the importance of some of these deductions 
 evident by experiment, and perhaps for the first time 
 exhibits them in their true import. 
 
 " This memoir is essentially a presentation of experi- 
 ments alone, without hypotheses, and with only such 
 indispensable formulae as are needed to link the obser- 
 vations together. These experiments furnish results 
 which may be succinctly summarized as follows : 
 
 " The primary experiment with the suspended plane 
 is not intended per se to establish a new fact, but to en- 
 force attention to the neglected consequences of the 
 fundamental principle that the pressure of a fluid is 
 always normal to a surface moving in it, some of these 
 consequences being (1) that the stress necessary to sus- 
 tain a body in the air is less when this is in horizontal 
 motion than when at rest ; (2) that this stress, instead 
 of increasing, diminishes with the increase of the hori- 
 zontal velocity (a fact at variance with the conclusions 
 of some physicists of repute, and with ideas still popu- 
 larly held) ; (3) that it is at least probable that in such 
 horizontal flight up to great velocities the greater the 
 speed the less the power required to maintain it, this 
 probability being already indicated by this illustrative 
 experiment, while demonstrative evidence follows later. 
 
 "The experiments which are presented . . . result 
 in an empirical curve, giving the ratio between the 
 pressure on an inclined square plane and on a normal 
 plane moving in the air with the same velocity. Inci- 
 dentally it is shown that the pressure is normal to the 
 inclined surface, and hence that the effects of skin fric- 
 tion, viscosity, and the like, are negligible in such ex- 
 periments. It is also shown that for the small angles 
 
180 AERIAL NAVIGATION. 
 
 most used in actual trial of the plane, the pressure on it 
 is about twenty times greater than that assignable from 
 the theoretical formula derived from Newton's discussion 
 of this subject in the Principia. This last experimental 
 result is not presented as a new contribution to knowl- 
 edge, since it had previously been obtained by experi- 
 menters in the early part of this century ; but as their 
 results appear not to have met with the general atten- 
 tion or acceptance they deserve, it is not superfluous 
 either to produce this independent experimental evi- 
 dence or to urge its importance. 
 
 "The experiments with the plane-dropper introduce 
 matter believed to be novel as well as important. They 
 show (1) that. the time of falling of a horizontal plane 
 is greater when moving horizontally than when at rest, 
 and (2) that this time of falling most notably increases 
 with the velocity of lateral translation ; (3) experiments 
 with different horizontal planes show that this increase 
 in the time of falling is greater for those planes whose 
 extension from front to back is small compared with 
 their length measured perpendicular to the line of ad- 
 vance ; (4) the horizontal velocities are determined at 
 which variously shaped inclined planes set at varying 
 angles can soar that is, just sustain their own weight 
 in the air under such circumstances and these data 
 afford the numerical basis for the important proposition 
 that the power required to maintain the horizontal mo- 
 tion of an inclined aeroplane is less for high speeds than 
 for low ones ; (5) by experiments with double planes, 
 one above the other, it is shown that planes of the ad- 
 vantageous shape mentioned above do not interfere with 
 each other at specified speeds, if so placed at an interval 
 not less than their length from front to back ; and it is 
 pointed out that an extension of this method enables us 
 
PROF. LANGLEY'S EXPERIMENTS. 181 
 
 to determine the extent to which any underlying air 
 stratum is disturbed during the plane's passage. 
 
 " The conclusions as to the weights which can be 
 transported in horizontal flight have included the ex- 
 perimental demonstration that the air friction is neg- 
 ligible within the limits of experiment. It has not been 
 thought necessary to present any evidence that an engine 
 or other adjunct which might be applied to give these 
 planes motion, need itself oppose no other than frictional 
 resistance, if inclosed in a stream-line form, since the 
 fact that such forms oppose no other resistance what- 
 ever to fluid motion has been abundantly demonstrated 
 by Froude, Kankine, and others. 
 
 " The most important general inference from these 
 experiments, as a whole, is that, so far as the mere power 
 to sustain heavy bodies in the air by mechanical flight 
 goes, such mechanical flight is possible with engines we 
 now possess, since effective steam engines have lately 
 been built weighing less than ten pounds to one horse- 
 power ; and the experiments show that if we multiply 
 the small planes which have been actually used, or as- 
 sume a larger plane to have approximately the proper- 
 ties of similar small ones, one horse power rightly ap- 
 plied can sustain over two hundred pounds in the air at 
 a horizontal velocity of over twenty metres per second 
 (about forty-five miles an hour), and still more at still 
 higher velocities. These numerical values are contained 
 in the following table.* It is scarcely necessary to ob- 
 serve that the planes have been designedly loaded till 
 they weighed five hundred grammes each, and that such 
 a system, if used for actual flight, need weigh but a 
 
 * See table, p. 135. 
 
182 AERIAL NAVIGATION. 
 
 small fraction of this amount, leaving the rest of the 
 sustainable weight indicated disposable for engines and 
 other purposes. I have found, in experiment, that sur- 
 faces approximately plane and of 1*10 this weight are 
 sufficiently strong for all necessary purposes of support. 
 
 " I am not prepared to say that the relations of power, 
 area, weight, and speed, here experimentally established 
 for planes of small area, will hold for indefinitely large 
 ones ; but, from all the circumstances of experiment, I 
 can entertain no doubt that they do so hold far enough 
 to afford assurance that we can transport (with fuel for 
 11 considerable journey and at speeds high enough to 
 make us independent of ordinary wind) weights many 
 times greater than that of a man. 
 
 " In this mode of supporting a body in the air, its 
 specific gravity, instead of being, as heretofore, a matter 
 of primary importance, is a matter of indifference, the 
 support being derived essentially from the inertia and 
 elasticity of the air on which the body is made to 
 rapidly run. The most important and, it is believed, 
 novel truth, already announced, immediately follows 
 from what has been shown, that whereas in land or 
 marine transport increased speed is maintained only by 
 a disproportionate expenditure of power, within the 
 limits of experiment in such aerial horizontal transport, 
 the higher speeds are more economical of power than the 
 loiver ones. 
 
 " While calling attention to these important and as 
 yet little known truths, I desire to add, as a final cau- 
 tion, that I have not asserted that planes such as are 
 here employed in experiment, or even that planes of 
 any kind, are the best forms to use in mechanical flight, 
 and that I have also not asserted, without qualification, 
 that mechanical flight is practically possible, since this 
 
PROF. LANGLEY'S EXPERIMENTS. 183 
 
 involves questions as to the method of constructing the 
 mechanism, of securing its safe ascent and descent, and 
 also of securing the indispensable condition for the eco- 
 nomic use of the power I have shown to be at our dis- 
 posal the condition, I mean, of our ability to guide it 
 in the desired horizontal direction during transport 
 questions which, in my opinion, are only to be answered 
 by further experiment, and which belong to the in- 
 choate art or science of aerodromics, on which I do not 
 enter. 
 
 " I wish, however, to put on record my belief that the 
 time has come for these questions to engage the serious 
 attention not only of engineers but of all interested in 
 the possibly near practical solution of a problem, one of 
 the most important in its consequences of any which 
 has ever presented itself in mechanics ; for this solution, 
 it is here shown, cannot longer be considered beyond 
 our capacity to reach." 
 
STUDY OF A PRACTICAL AIR SHIP. 
 
 IK a paper published in Cassier's Magazine of Feb- 
 ruary, 1893, Mr. John P. Holland presented a very in- 
 teresting study of a practical air ship. The following 
 extracts and illustrations, reproduced through the 
 courtesy of The Gassier Magazine Company, indicate, 
 in a general way, Mr. Holland's suggestions as to the 
 form and construction of such a machine : 
 
 It may assist in our study to consider what condi- 
 tions are required in an aerial machine, in order that it 
 may be safe for the experimenter, and capable of travel- 
 ling a considerable distance under perfect control, and 
 at good speed, and then to find whether we have the 
 requisite means available. 
 
 1. It must be strong enough to endure all the strains 
 to which it may be subjected, and have a considerable 
 margin of safety or strength remaining. 
 
 If we employ steel for every part subject to tensile 
 strains, hard-seasoned ash for those enduring compres- 
 sion, and silk for covering the aeroplanes, screws or 
 wings, and body of our machine, there will be no occa- 
 sion for employing any expensive or untried material in 
 our experiments. This shall be shown later when we 
 come to examine the functions of the parts that may be 
 required in a practicable flying machine. 
 
STUDY OF A PRACTICAL AIR SHIP. 185 
 
 13 
 
186 AERIAL NAVIGATION. 
 
 2. The aeronaut must be able to alight without 
 shock or injury to himself or his machine; because, 
 until this is assured, no one will be willing to risk 
 getting a broken neck in the interest of aero- 
 nautics. 
 
 This is a simple matter in a machine that employs a 
 pair of propeller screws on concentric or parallel axes 
 capable of inclination between the horizontal and verti- 
 cal positions, in connection with aeroplane surface of 
 ample area. As a machine of this kind should be able 
 to rise from a level surface, in still air, the power that 
 lifts it, when rising, can be reduced so as to regulate its 
 speed of descent and cause it to rest on the ground 
 without injury. 
 
 If the power employed be not sufficient to lift the 
 total weight directly, although it be enough to support 
 it with the assistance of aeroplanes when moving hori- 
 zontally, the rise and descent must be made against a 
 strong wind, or the machine must be launched from an 
 elevated position when starting, and rise from a low to 
 a higher level, and rest on some elevated place when the 
 energy due to its speed is absorbed. Observers of Na- 
 ture notice that birds of all sizes face the wind, when it 
 is considerable, both in rising and descending. The 
 larger birds select elevated points, such as rocks or 
 tree branches, on which to rest, so as to be able to 
 launch themselves and attain full speed of flight with 
 the least delay and exertion. It has also been observed 
 that they reach those resting-places neither by descend- 
 ing nor by horizontal movement, but by rising from a 
 lower level and alighting after a few vigorous wing- 
 strokes against the direction of motion. 
 
 3. The machine must be able to travel at good speed, 
 say thirty miles per hour at least, and steadily that is, 
 
STUDY OF A PRACTICAL AIR SHIP. 187 
 
 without any tendency to plunging or diving, like an un- 
 balanced kite. 
 
 The speed depends on the amount of power avail- 
 able and on the smallness of the surface and bulk rela- 
 tively to the weight. For example, a vulture can travel 
 six times faster than a crow, but it has only one third 
 as much wing surface in proportion to its weight. One 
 horse power, equal to 550 foot-pounds per second, ap- 
 plied to towing a flat aeroplane 184 square feet in area, 
 weighing 118 pounds, and set at an angle of six degrees, 
 at a speed of twenty-five miles per hour, equal to 36-66 
 feet per second, will overcome a resistance of 550 -f- 
 36*66 = 15 pounds while doing that work. 
 
 If the inclination of the plaae be reduced to one de- 
 gree and the speed made six times greater, the reduction 
 of the angle reduces the lifting power to one sixth, but 
 the increased speed raises it again as the square, or 
 thirty-six times 36 X J = 6. Therefore the same plane 
 lifts six times as much with the new inclination and 
 speed, and the original weight will be supported at the 
 new speed with one sixth of the plane area. 
 
 The reduction of angle reduces the drift to one thir- 
 ty-sixth, and the increase of speed raises it again thirty- 
 six times, restoring the original resistance, fifteen pounds. 
 When we reduce the plane area to one sixth, equal to 
 30'66 square feet, we reduce the drift to 2'5 pounds ; but 
 as it is exerted through six times the space in the same 
 time, the work performed remains the same 2*5 X 36f 
 X 6 = 550 foot-pounds = 1 horse power. Before the 
 angle was reduced and the speed increased the propor- 
 tion stood 1'56 square feet per pound weight. After 
 the change was made the proportion became 0'166 square 
 foot per pound weight. 
 
 If our machine have the speed, surface, and inclina- 
 
188 AfiRIAL NAVIGATION. 
 
 tion of aeroplanes necessary to support its weight it will 
 fly just as steadily as a properly balanced kite if corre- 
 sponding conditions are observed that is, if the centre 
 of gravity is at a proper distance vertically under the 
 centre of pressure or support, and if the point at which 
 towing power or thrust is applied is on the intersection 
 of the horizontal and vertical planes passing through the 
 centre of pressure or resistance. 
 
 The chief problem awaiting solution, in the opinion 
 of some investigators, is to find a reliable method of con- 
 trolling its motions in the air, the power question having 
 been disposed of long ago by the construction of tor- 
 pedo-boat motors weighing sixty pounds per horse 
 power ; the Norwood's, nineteen pounds per horse 
 power; Mr. Stringfellow's steam motor, weighing thir- 
 teen pounds per horse power ; and Mr. Maxim's, weigh- 
 ing nine pounds per horse power. The impracticability 
 of holding a thin, weak plane to its work when the speed 
 is high and the inclination under two degrees to the 
 horizontal, is the basis of this difficulty. Under these 
 conditions the plane is liable to vibrate, and to lie some- 
 times parallel with its direction of motion, or to dip its 
 leading edge or one of its sides, thus sustaining pressure 
 on its upper surface on the part depressed, and causing 
 the machine it supports to tip sidewise or plunge down- 
 ward ahead. With these difficulties to encounter, steady 
 horizontal motion and steering would be puzzling prob- 
 lems. However, we can avoid instead of meeting them 
 by forming our aeroplanes in narrow superposed sections,, 
 placed far enough apart to prevent interference with 
 each other, and by making the upper surface convex, 
 with the greatest rise near the leading edge, and the 
 under or pressure side slightly concave. Mr. Horatio 
 Phillips has proved that this change increases the effi- 
 
STUDY OP A PRACTICAL AIK SHIP. 
 
 189 
 
 ciency in lifting 2*74 times without increasing the tow- 
 ing or drift force, and that a plane of this section left 
 free to set its own inclination being held near the lead- 
 ing edge, would lie with its posterior or trailing edge 
 at a higher level than its anterior or leading edge. As 
 the curved shape of the upper and under surfaces, and 
 the thick space between them, afford facilities for stiffen- 
 ing the places, neither weakness nor vibration may be 
 expected, and there remains only the question of steer- 
 ing a body immersed in a fluid, as a submarine boat or 
 automobile torpedo when running submerged. It is 
 clear that these cases are analogous, and that the aerial 
 machine, when properly designed and constructed, can 
 be as easily steered in every direction as the submarine 
 boat, and by similar manual or automatic devices. 
 
 If we take some bird for the model of our machine 
 and adopt its method of rising, progressing, and de- 
 scending, the surface, weight, power, and speed will bear 
 a certain proportion to each of these particulars in the 
 
 FIG 22. APPEARANCE OF FLYING MACHINE FROM EN FRONT. 
 
 bird, provided the mechanical efficiency in each case is 
 equal. But as this is unattainable, greater proportionate 
 power must be provided. Some modification of other 
 particulars must also be made to fit it for being con- 
 trolled by a more inexperienced operator. 
 
190 AERIAL NAVIGATION. 
 
 The rules relating to the ratios between models and 
 the things they represent may be quoted as follows : 
 
 Proportionate power is as the cube of the ratio of 
 some similar linear dimensions. 
 
 Proportionate weight is in the same ratio. 
 
 Proportionate surface is as the square of the ratio of 
 similar linear dimensions. 
 
 Proportionate speed is as the square root of the ratio 
 of similar linear dimensions. 
 
 Having advanced reasons for believing that a man 
 can fly with wings, our next step will be to find whether 
 a practicable solution of the problem of air navigation is 
 attainable with a machine of simple design and of less 
 exact construction than is required in one modelled on a, 
 bird. 
 
 The question stands thus : Can we build a kite, or its 
 equivalent, large and strong enough, and push or tow it 
 fast enough through the air to support itself, its motor 
 and accessories, and some weight besides its operators? 
 Can we cause it to rise from a level and descend without 
 accident, and travel steadily in any desired direction? 
 
 A study of the things available and what we require 
 of them will assist us to estimate our chances of success. 
 
 The size and capacity of our machine and its acces- 
 sories will be determined by the power of the motor em- 
 ployed, and this must be large, because a small one will 
 not do as much work in proportion to its weight and 
 consumption of fuel that is, it cannot be so economical. 
 
 Suppose we employ steam engines and a boiler capa- 
 ble of indicating four hundred horse power and a pair 
 of air propeller wheels revolving in opposite directions. 
 
 We will deduct ten per cent for friction in the ma- 
 chinery, and if our air propellers prove to be as effective 
 as some that have been tested they will give an efficiency 
 
STUDY OP A PRACTICAL AIR SHIP. 
 
192 AERIAL NAVIGATION. 
 
 of over eighty per cent, thus rendering effective seventy- 
 two per cent, or two hundred and eighty-eight of the 
 four hundred indicated horse power. 
 
 The propeller wheels are placed on parallel or con- 
 centric axes capable of inclining from the vertical to the 
 horizontal position, and vice versa. Their power is first 
 applied to lifting the machine vertically. When all ele- 
 vated objects are cleared, the screw shafts are gradually 
 inclined from the vertical, thus bringing a horizontal 
 force, proportional to the size of the angle of inclination 
 to the vertical into action at the expense of the elevating 
 force. The latter can afford to suffer a considerable 
 diminution before being reduced to a point at which it 
 could no longer support the weight of the machine, be- 
 cause the weight to be lifted must be so proportioned 
 that the power cannot only lift it at the start, but also 
 give it a considerable upward velocity, say three feet per 
 second. The weight multiplied by this speed is equal to 
 the power spent in imparting upward velocity while as- 
 cending, and also what is available for beginning hori- 
 zontal motion, and calling the aeroplanes into action. 
 Every succeeding degree added to the inclination re- 
 duces the direct lift ; but as there is a corresponding 
 supporting power developed by the aeroplanes, the ma- 
 chine will lose nothing in elevation. This process con- 
 tinues until all the power is applied directly to propul- 
 sion or drift, the weight of the machine being supported 
 by the corresponding lifting power developed by the 
 aeroplanes. 
 
 In order to descend, the method of managing the as- 
 cent must be reversed, but the operation may be com- 
 pleted much more rapidly. In both cases the speed of 
 the wind must be taken account of by facing the wind 
 and by beginning the ascent and finishing the descent 
 
STUDY OF A PRACTICAL AIR SHIP. 
 
 193 
 
194 AERIAL NAVIGATION. 
 
 with an inclination of the screw shafts, capable of im- 
 parting a horizontal velocity that compensates for the 
 wind's speed in the opposite direction. The path, both 
 in ascent and descent, will be represented by a vertical 
 and a horizontal line connected by a curve to which each 
 will be tangent. 
 
 The lifting power of screws next claims considera- 
 tion ; and it may be said that the experiments made 
 with this object in view, the particulars of which have 
 been published, have been indecisive and unsatisfactory, 
 owing chiefly to the unsuitable proportions of the screws 
 employed. Other defects have interfered with efficiency 
 in some cases, but this one was found present invariably. 
 
 Mr. Maxim did not construct his screws for lifting, 
 but to be effective when moving horizontally, and for 
 that purpose they appear to be unexcelled. A combina- 
 tion of the two qualities great lifting power and effi- 
 ciency when moving rapidly is what we require, and it 
 is evident that we shall have it if we can construct a 
 screw having a very short pitch or small inclination 
 relatively to its transverse axis while it is employed in 
 lifting, and that can automatically alter its pitch as the 
 thrust or lifting power is reduced. There are many de- 
 vices in existence for so changing the pitch, and almost 
 any of them will answer our purpose. The efficiency in 
 pushing was, with one of Mr. Maxim's screws, 81'45 per 
 cent. One horse power per second is 550 pounds lifted 
 one foot. The same percentage of this will be 550 X 
 81-45 = 447-97 foot-pounds. That is, one horse power 
 can lift 447 pounds one foot high per second with either 
 screw or aeroplane when properly designed. We want 
 to lift our machine three feet high per second, therefore 
 it may have a weight of 447 -f- 3 = 149 pounds per ef- 
 fective horse power provided. This degree of efficiency 
 
STUDY OF A PRACTICAL AIR SHIP. 
 
 195 
 
 would be quite unattainable with flat surfaces in screws 
 and aeroplanes, and even if it were approached it could 
 not be maintained with the materials suitable for a fly- 
 ing machine on account of their want of rigidity and 
 stability when set at small angles. 
 
 The accompanying diagram (see Fig. 25) may suggest 
 an explanation of the great efficiency of the convexed 
 and concaved planes. The direction of motion of plane 
 is indicated by the arrow on its section. The air-stream 
 
 FIG. 25. PROBABLE ARRANGEMENT OF STREAM LINES DURING MOVEMENT OF 
 CONVEXED AND CONCAVED PLANE. 
 
 lines begin to be formed in advance of the plane, acting 
 as if they felt its approach, and dividing at a slightly 
 higher level than its leading edge. Those that pass be- 
 low are bent downward, but recurve quickly, owing to 
 the fluid pressure and the elasticity of the air, and they 
 strike the under side of the blade in a direction ap- 
 proaching the normal on account of the recurving and 
 the concaving of the surface. The part that recurves 
 has its effectiveness increased as the square of the ve- 
 locity due to elasticity, and this is in addition to the 
 pressure due to the speed of passage and inclination of 
 the blade. 
 
 The stream lines passing over the blade are bent up- 
 ward and left behind by the rapidly advancing plane. 
 The elasticity and pressure of the air cause them to 
 
196 AfiRIAL NAVIGATION. 
 
 recurve downward, but not fast enough to lie against 
 the back of the plane, where in consequence defective 
 pressure must exist. This defective pressure or partial 
 vacuum is made more intense by the rubbing of the 
 streams against what air may follow the blade, thus 
 drawing it away by friction or suction, and its intensity 
 is increased probably as the square of the speed up to 
 perfect vacuum. As the partial vacuum on the back is 
 exerted in a direction opposite to the line of progress of 
 tho plane, it is just as effective as an equivalent positive 
 pressure against the under side of the plane. 
 
 An air screw with a flat under surface and convexed 
 back will operate efficiently when both the leading and 
 trailing edges are on the plane of the direction of mo- 
 tion of the blades that is, when the apparent angle of 
 incidence of the air on the under surface is nothing. 
 This condition of negative slip in marine screws is 
 wasteful of power on account of the great increase of 
 friction ; but it is well known that, when all longitudinal 
 sections are ship-shaped, the question of air friction 
 may be neglected with aerial machines. 
 
 We have available 288 effective horse power, and it 
 has been shown that we can lift 149 pounds per horse 
 power and elevate it at a speed of three feet per second. 
 If the speed of rising be reduced, the weight may be 
 increased correspondingly. 
 
 149 X 288 = 42,912 pounds. . 
 
 With a lifting force of 149 pounds per horse power 
 at our disposal, there is scarcely any necessity for ex- 
 pending much ingenuity in the construction of very 
 light engines, especially if they prove to be very costly. 
 Motors similar to those employed on some launches, but 
 modified to suit the circumstances, would serve our pur- 
 pose quite well enough. We shall find, however, that a 
 
STUDY OF A PRACTICAL AIR SHIP. 197 
 
 motor of great strength and lightness can be built for 
 very little more money than should be paid for first-class 
 launch engines, specially built. Prof. Albert F. Zahm 
 has shown us how a very light boiler may be built. " A 
 boiler, for example, of quarter-inch tubes possesses six- 
 teen times as much heating surface, and consequently 
 sixteen times as much evaporative power, as a boiler of 
 equal weight of four-inch tubes." For the same power 
 the weight would then be only one sixteenth. 
 
 The action of the motor may be made perfectly au- 
 tomatic, as the fuel burned will be petroleum. It will 
 require no extra care in handling, as there will be no 
 variation of the power from the start until it is reduced 
 when preparing to descend. The relative gain of power 
 due to reduction of weight by fuel consumption will be 
 spent on increasing the speed. 
 
 In order that our machine may be compact, yet 
 speedy and manageable, we must have as little aeroplane 
 surface, and of as little spread, as possible. To deter- 
 mine its area we must find what speed can be made. 
 
 Two hundred and eighty-eight horse power is equal 
 to 158,400 foot-pounds per second. 
 
 Xinety miles speed per hour is equal to 132 feet per 
 second ; 158,400 foot-pounds -j- 132 feet per second is 
 equal to 1,200 pounds drift force. 
 
 Total lifting power 42,912 _ 
 
 Total drift power 1,200 ~~ 
 
 35-67 = ratio of lift to drift force. 
 
 Ratio of lift to drift 35-67 _ 
 
 Coefficient for con vexed planes. 2-?4 ~ 
 ratio of lift to drift for fiat plane with square edges. 
 By consulting Mr. Chanute's table we shall find that 
 this corresponds with an inclination of about 4*5 de- 
 grees. The wind pressure due to ninety miles speed 
 
198 AERIAL NAVIGATION. 
 
 40-5 pounds multiplied by the drift coefficient for 4-5 
 degrees, gives the drift pressure per square foot of aero- 
 plane : 
 
 40-5 X 0-01245 = 0-5042 pounds drift per square foot. 
 
 Total drift force, 1,200 pounds, divided by drift per 
 square foot. 
 
 0-01245 gives the extent of aeroplane surface re- 
 quired. 
 
 " = 2,379 square feet surface. 
 
 0-01245 
 
 This surface may be most conveniently disposed by 
 arranging it in fifteen superposed planes, each eighty 
 feet long, two feet wide, and spaced two feet apart. 
 
 The spindle-shaped body of the machine that carries 
 the machinery and operators will be placed under the 
 centre of the set of planes, with the axes of the screws 
 slightly under the centre of pressure when moving hori- 
 zontally. The centre of gravity may be four to six feet 
 under the centres of pressure and support by this ar- 
 rangement. (See Figs. 23 and 24.) 
 
 The trussed frame carrying the engines and screws 
 will be solidly connected to the frame carrying the aero- 
 planes, the screw shafts being placed at right angles 
 with the plane of their trunnioned ends. The aero- 
 planes, engines, and screws revolve together through 
 ninety degrees during the change from vertical to hori- 
 zontal motion during the ascent, and return during the 
 descent. 
 
 In_prder to make room for the body and screws, an 
 open space must be provided in the set of aeroplanes, 
 and compensation for the corresponding loss of surface 
 must be made by adding a sixteenth plane. 
 
 When the machine lies on the ground the aeroplane 
 frame will be nearly horizontal, and it will stand nearly 
 
STUDY OF A PRACTICAL AIR SHIP. 199 
 
 at right angles to the axis of the body when moving 
 horizontally. (See Figs. 21 and 24.) 
 
 As we have so large a margin of carrying power, 
 there is no necessity for going closely into an estimate 
 of the weight. Each aeroplane will require the equiva- 
 lent of an ash pole eighty feet long, and about two and a 
 half inches in diameter. The frame carrying it will re- 
 quire two thirty-foot pieces about one inch thick, and 
 six inches wide at the centre. The body will require 
 the equivalent of four sixty-foot pieces about three 
 inches in diameter, with a small floor and hoops. 
 
 The wood required for the whole structure may be 
 roughly estimated as equal to twenty-four eighty-foot 
 poles, two and a half inches in diameter, and tapering 
 to the ends. Their weight will be 
 
 24 x 80 X -034 square feet X .6 for taper X 50 pounds 
 = 1,958 pounds. 
 
 Allow one half as much for ribbon stays of steel, and 
 ash struts, say 1,000 pounds total, 3,000 pounds. 
 
 The machine weighs 3,000 pounds. 
 
 The motor complete and water, 5,200 pounds. 
 
 Total weight of machine and motor, 8,200 pounds. 
 
 Total weight, j^200' =28 . 4 poimds per effective 
 
 Effective power, 288 
 horse power. 
 
 It is clear that everything may be four times heavier 
 and yet be within practicable limits. 
 
 The consumption of petroleum will be about one 
 pound per horse power per hour. The mean weight, if 
 only oil for fuel be carried, is equal to one half the sum 
 of the total lifting power, and the weight of the com- 
 plete machine, without fuel : 
 
 42,912 + 8,200 . 
 
200 AERIAL NAVIGATION. 
 
 ing power of one horse power gives the mean power 
 required. 
 
 25,556 -f- 149 = 175 horse power. As each horse 
 power requires one pound of oil, there will be a mean 
 consumption of 175 pounds per hour. Carrying pow- 
 er, 42,912 8,200 = 34,712 pounds of oil ; say 34,000 
 pounds, to allow for crew and supplies. 
 
 34,000^174 = 194 hours' flight, and supposing the 
 mean speed to be no higher than ninety miles per hour, 
 the distance covered will be 194 X 90 =17,460 miles, or 
 about one half that distance with one half of the carry- 
 ing capacity devoted to fuel and the remainder to cargo. 
 
THE SOARING OF BIRDS AND OF MEN. 
 
 NOTHING connected with the study of problems of 
 aerial navigation has engaged more attention, and noth- 
 ing has remained more completely within the domain 
 of speculation, than the means by which soaring birds 
 maintain their elevation and the constancy of their 
 movement in the air, with wings motionless, and every 
 feather apparently at rest. The explanation of such 
 soaring has been sought by scientific men for a century 
 past. 
 
 At last light seems to have been thrown on this also 
 by a paper prepared by Prof. Langley for the Confer- 
 ence on Aerial Navigation, at Chicago, in 1893. He 
 furnishes a possible explanation of soaring in connec- 
 tion with what he calls "The Internal Work of the 
 Wind." Very briefly stated, he finds by careful experi- 
 ment that the movement of given portions of the air in 
 the advancing mass constituting wind is not the steady 
 movement of the wind itself. These individual portions 
 of the whole volume change their velocity much more 
 frequently and to a much greater extent than had here- 
 tofore been supposed. For example, let it be supposed 
 that the velocity of the moving mass of the atmosphere 
 14 
 
AfiRIAL NAVIGATION. 
 
 being twenty-five miles per hour, the velocity of inte- 
 gral parts may vary within minutes, or even within sec- 
 onds, from an apparent calm to a velocity of fifty miles 
 per hour. In this case, a heavy body carried by the 
 wind at its mean velocity of twenty-five miles per hour, 
 would, when passing through a period of total calm, be 
 subjected to an impulse from the front of twenty-five 
 miles per hour, and during the period of fifty miles for- 
 ward velocity to an impulse from the rear of twenty- 
 five miles per hour. Soaring birds are heavy, and their 
 weight tends to maintain by inertia the velocity with 
 which the general movement of the current propels 
 them. They have, therefore, viewed as aeroplanes, only 
 to elevate their forward edges during a calm, and their 
 rear edges during an air movement greater than the 
 mean velocity of the wind, to be in command of a lifting 
 power which calls for no material muscular exertion. 
 Having gained a higher elevation, they can soar forward 
 with a slight descent against a strong wind. 
 
 This is hardly more than an intimation of the elabo- 
 rate, carefully worked out and illustrated theory by 
 which Prof. Langley seems not only to account for the 
 soaring of birds, but to demonstrate the possibility of a 
 like power to be gained for soaring machines or aero- 
 planes having sufficient weight to maintain their inertia. 
 He evidently believes it possible that, "by the use of this 
 internal work of the wind, flying machines may be made 
 to travel, except during calms, without making use of 
 their motor appliances, or, to use his own words : " Fi- 
 
THE SOARING OF BIRDS AND OF MEN. 203 
 
 nally, these observations and deductions have, it seems 
 to me, an important practical application, not only as 
 regards a living creature, like the soaring bird, but still 
 more as regards a mechanically constructed body, whose 
 specific gravity may probably be many hundred or even 
 many thousand times that of the atmosphere. We may 
 suppose such a body to be supplied with fuel and en- 
 gines, which would be indispensable to sustain it in a 
 calm, and yet which we now see might be ordinarily left 
 entirely inactive, so that the body could supposably re- 
 main in the air and even maintain its motion in any di- 
 rection without expending its energy, except as regards 
 the act of changing the inclination or aspect which it 
 presents to the wind while the wind blew. 
 
 " The final application of these principles to the art 
 of aerodromics seems, then, to be that, while it is not 
 likely that the perfected aerodrome will ever be able to 
 dispense altogether with the ability to rely at intervals 
 on some internal source of power, it will not be indis- 
 pensable that this aerodrome of the future shall, in 
 order to go any distance even to circumnavigate the 
 globe without alighting need to carry a weight of fuel 
 which would enable it to perform this journey under 
 conditions analogous to those of a steamship, but that 
 the fuel and weight need only be such as to enable it to 
 take care of itself in exceptional moments of calm." 
 
INDEX. 
 
 Accidents to air ships in flight, 
 
 effect of, 161. 
 Aerial navigation, compared with 
 
 railroad travel, 127, 160. 
 Aeroplane, aspects of, 133. 
 
 bird an animated, 112, 113. 
 
 compared with skaters on thin 
 ice, 171, 177. 
 
 computation of capacity by ve- 
 locity and angle, 115. 
 
 efficiency dependent on propor- 
 tion of width to length and on 
 aspect, 170. 
 
 form of, 189. 
 
 influence of edge, 154. 
 
 influence of velocity on support- 
 ing power and on force re- 
 quired for propulsion, 138. 
 
 load supported per horse power, 
 139. 
 
 moving at an angle creates resist- 
 ance, 114. 
 
 optima angle for, 115. 
 
 should travel at least thirty miles 
 per hour, 186. 
 
 specific gravity a matter of in- 
 difference with, 182. 
 
 suggested by Maxim, 142. 
 
 to rise and descend against the 
 
 wind, 186. 
 
 Aeroplanes, Langley's experimen- 
 tal, 131. 
 
 soaring of, 171. 
 
 Aeroplanes, stream lines for, 155. 
 superposed, 134, 138, 173, 198. 
 with sufficient velocity, air acts 
 
 as solid support for, 171. 
 Air friction, negligible within cer- 
 tain limits, 129, 159, 181. 
 Air ship in calm weather, 32. 
 Anchored balloons, 40. 
 Atmospheric currents, 104. 
 pressure, elevation, and ballast, 
 
 29. 
 Avanzini, law of, 94. 
 
 Backflow, or slip, 138, 177. 
 Ballast, atmospheric pressure and 
 
 elevation, 29. 
 Balloon, an unstable buoy, 30. 
 
 as air ship, requirements of, 37. 
 
 first sent up by Montgolfier, 2. 
 
 first sent up with gas, 3. 
 
 first ascent with passengers, 3. 
 
 " La France," experiment with, 59. 
 Balloons, anchored, 40. 
 
 at various elevations, 28. 
 
 compared with buoys, 23, 30. 
 
 compared with submerged ves- 
 sels, 25. 
 
 conclusions concerning, 117. 
 
 early improvements in, 4. 
 
 in French army in Tonquin, 11. 
 
 in military manoeuvres in France, 
 10, 13. 
 
 in the Dutch army, 17. 
 
206 
 
 AERIAL NAVIGATION. 
 
 Balloons, results reached in propel- 
 ling machinery for, 52. 
 results reached with different 
 
 forms, 57. 
 
 Bird, an animated aeroplane, 113. 
 Birds' flight, 5, 64, 73. 
 force consumed in, 74, 101. 
 less exertion expended in full 
 flight than in its beginning, 75. 
 Birds, number of wing-strokes per 
 
 second, 76. 
 
 Birds' speed depends on smallness 
 of bulk relatively to weight, 
 187. 
 Birds' wings, double function of, 
 
 121. 
 
 movable aeroplanes, 112. 
 Boy's kite, 69. 
 
 Bretonniere, computation of angles 
 in the hovering of the stork, 
 85. 
 
 Calm weather, air ship in, 32. 
 
 Capacity of aeroplane, computed by 
 velocity and angle, 115. 
 
 Centrifugal force, effects on experi- 
 ments with whirling table, 140. 
 
 Chalais, aerostatic installation, 53. 
 experiments at, 34. 
 
 Chanute's elements of resistance, 
 159. 
 
 Currents, atmospheric, 104. 
 
 Drzewiecki, calculations, 110, 112. 
 on double function of birds' 
 
 wings, 121. 
 
 results of his investigations, 121. 
 Dupuy de Lome, improvements in 
 elongated balloons, 117. 
 
 Eiffel Tower, meteorological obser- 
 vations at, 5, 106. 
 Electric motors, 54. 
 
 Elevation, atmospheric pressure, 
 
 and ballast, 29. 
 
 Elongated balloons, stability of. 117. 
 Engines ; see MOTORS, also STEAM 
 
 ENGINES. 
 Experiments in aerodynamics, 167. 
 
 Falcon, flight of, 81, 101. 
 Flight of birds, 5, 64, 73. 
 force consumed, 74. 
 more exertion expended in be- 
 ginning than in continuing, 75. 
 Flight, rowing, 73. 
 sailing, 89. 
 
 sailing, only in wind, 126. 
 sailing, compared with sailing of 
 
 boats, 90. 
 
 soaring, only in calm, 126. 
 Floating or soaring appliances, 109. 
 Flying machines, accidents, to, 161. 
 angle and drift of, 187. 
 Maxim's experimental, 142. 
 should travel at least thirty miles 
 
 per hour, 186. 
 speed depends -on smallness of 
 
 bulk relative to weight, 187. 
 steering, 188. 
 to rise and descend against the 
 
 wind, 186. 
 Freninge's propeller wheel, 151, 
 
 159. 
 
 Friction, skin, negligible, 129, 159, 
 181. 
 
 Galvanic columns, 54. 
 Gas, hydrogen, lifting force of, 26. 
 Giffard's increase of length of bal- 
 loons, 117. 
 
 Holland, John P., action of screws 
 in rising, travelling, and land- 
 ing, 153. 
 
 calculations for construction of 
 practical machine, 160. 
 
INDEX. 
 
 207 
 
 Holland, John P., conditions re- 
 quired, 184. 
 flying machine with two broad 
 
 aeroplanes, 156. 
 flying machine with superposed 
 
 planes, 162, 164, 165, 184, 188. 
 flying machines, carrying power 
 
 of, 160. 
 
 paper in Cassier's Magazine, 184. 
 prize paper in Cosmopolitan 
 
 Magazine, 149. 
 recommends screw propeller and 
 
 aeroplanes, 149. 
 requirements for navigating the 
 
 air, 149. 
 
 study of practical air ship, 184. 
 Horizontal speed, 132, 147, 171, 186. 
 
 thrust of screw, 136, 151, 175. 
 Hovering flight, 80. 
 
 angle of, 83, 87. 
 Hovering toys, 96, 99, 100, 101. 
 Hydrogen gas, lifting force of, 26. 
 
 Internal work of the wind, Lang- 
 ley, 201. 
 
 Jeffries, Dr. John, a Harvard grad- 
 uate, crossed Dover Straits, 
 1785, 3. 
 
 Kite, boy's, 69. 
 
 Krebs and Renard's experiments, 
 118. 
 
 Langley, Prof. S. P., aeroplane may 
 support nine times its own 
 weight, 182. 
 
 air friction negligible within cer- 
 tain limits, 181. 
 
 experimental aeroplanes. 131. 
 
 experiments in aerodynamics, 
 167. 
 
 internal work of the wind, 201. 
 
 mechanical flight possible with 
 engines now available, 181. 
 
 Langley, Prof. S. P., reference to 
 
 his experiments, 125. 
 study of screw propellers, 136. 
 summary of results of experi- 
 ments with propellers, 176. 
 whirling table, 169. 
 with aeroplanes specific grav- 
 ity a matter of indiflerence, 
 182. 
 u Le plus lourd que 1'air," 109, 
 
 120. 
 
 Lifting force of hydrogen. 26. 
 Load supported per horse power by 
 
 aeroplanes, 139. 
 Longitudinal instability, 34. 
 
 Marey. calculations of angles and 
 
 velocity, 86. 
 Maxim, H. S., aeroplanes suggested 
 
 by him, 142. 
 
 efficiency of his propellers, 194. 
 experiments in steering, 146. 
 method of trial recommended, 
 
 144. 
 prize paper in Cosmopolitan 
 
 Magazine, 144. 
 
 Mechanical flight, early experi- 
 ments in (foot-note), 2. 
 possible with means now avail- 
 able, 181. 
 
 Military importance of aerial navi- 
 gation, 10. 
 Montgolfier, sent up first balloon, 
 
 1783, 2. 
 
 Motors, comparison of, 55. 
 electric, 54. 
 
 examples of light, 150. 
 for balloons, relation of power to 
 weight in different experi- 
 ments, 118. 
 now available for mechanical 
 
 flight, 181. 
 
 weight per horse power, 139, 150, 
 188, 197. 
 
208 
 
 AERIAL NAVIGATION. 
 
 Nadar's balloon, " The Giant," 8. 
 balloon postal service during 
 
 siege of Paris, 10. 
 principle, " Le plus lourd que 
 
 1'air," 7, 9, 109, 120. 
 Nineteenth century may still see 
 practical results, 166. 
 
 Optima angle for aeroplanes, 115. 
 
 Parachute, 92. 
 
 Paris, siege of, balloon service dur- 
 ing, 10. 
 
 Petroleum as fuel, 199. 
 Photography, chronomctric, applied 
 
 by Marey, 5. 
 Plus lourd que 1'air ; see " LE PLUS 
 
 LOURD QUE L'AIR." 
 Power, effective, of motors, 196. 
 weight, surface, and speed, ratio 
 
 between, 190. 
 Propellers, screw, analogy between 
 
 aerial and marine, 178. 
 angle and form for blades, 196. 
 changing angle for lifting, for 
 driving, and for descending, 
 192. 
 
 different from windmill or sta- 
 tionary blower, 137, 176. 
 efficiency of, 136, 151, 175, 194. 
 Freninge's, 151, 159. 
 Holland's, 159. 
 
 Langley's experiments with, 136. 
 lifting power of, 151, 194. 
 maximum efficiency with small 
 
 number of blades, 137, 176. 
 with two blades glides on undis- 
 turbed strata of air. 177. 
 the higher the velocity the less 
 
 the slip, 177. 
 Propelling balloons, results reached 
 
 with machinery for, 52. 
 Propelling force decreases as ve- 
 locity increases, 130, 168, 175. 
 
 Railroad travel compared with aeri- 
 al navigation, 127. 
 Eenard, Commandant, 22. 
 experiments of, 52. 
 and Krebs, experiments of, 118. 
 Kesistance of aeroplane moving at 
 
 an angle, 114. 
 
 the elements of, Chanute's, 159. 
 Eowing flight, 73. 
 
 Sailing flight, 89. 
 compared with sailing of boats, 
 90. 
 
 Screws, action of, in rising, travel- 
 ling, and descending, 153. 
 
 Screw propellers ; see PROPELLERS. 
 
 Slip, 138, 177. 
 
 Soaring of birds and of men, 201. 
 
 Soaring velocities, 132. 
 
 Speed dependent on power, form, 
 
 size, and weight, 44. 
 with reference to that of the 
 
 wind, 45. 
 see also VELOCITY. 
 
 Specific gravity a matter of indif- 
 ference with aeroplanes, 182. 
 
 Stability of elongated balloons, 
 117. 
 
 Steam engines as motors, 191. 
 
 Steering, 6, 146, 188. 
 Maxim's experiments in, 146. 
 
 Storks, flight of, 83. 
 
 Stream-lines for aeroplanes, 129, 
 195. 
 
 Superposed aeroplanes, 134. 
 
 Surface friction may be disregarded, 
 129, 159, 181. 
 
 Swaying of flying machine in the 
 air, how prevented, 147. 
 
 Tissandier's improvements, 117. 
 Tonquin, balloon service in war 
 with, 11. 
 
INDEX. 
 
 Velocity, increased, secures firmer 
 
 support by the air, 77. 
 influence on supporting power 
 
 and on force required to propel 
 
 aeroplanes, 77, 138. 
 more important than lifting pow 
 
 er, 118. 
 of propellers, the higher, the less 
 
 the slip, 177. 
 of wind, 50. 
 required for practical solution of 
 
 the problem, 51. 
 see also SPEED. 
 
 Weight of engines and boilers, 150, 
 
 197. 
 
 of machine suggested by Holland, 
 199. 
 
 Weight per horse power that can 
 be supported by aeroplane, 
 139. 
 
 Whirling table (Langley's), 128. 
 Wind, as affecting the sailing of 
 
 air ships, 42. 
 as an obstacle, 38, 40. 
 does not exist for the aeronaut, 
 
 41. 
 
 internal work of the, 201. 
 maximum velocity of, 50. 
 Wings, angle of, in relation to ve- 
 locity, 86. 
 
 Wing-strokes, number per second 
 of different birds, 76. 
 
 Zones of equilibrium, 29. 
 
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 in South Africa. His grizzly bear is as dangerous as the lion, and his mountain sheep 
 and goats more difficult to stalk and shoot than any creatures of the torrid zone. Evi- 
 dently he came by his tastes as a hunter from litelong experience." New York 
 Tribune. 
 
 "The book has no dull pages, and is often excitingly interesting, and fully in- 
 structive as to the habits, haunts, and nature of wild beasts." Chicago Inter-Ocean. 
 
 "There is abundance of interesting incident in addition to the scientific element, 
 and the illustrations are numerous and highly graphic as to the big game met by the 
 hunters, and the hardships cheerfully undertaken. " Brooklyn Eagle. 
 
 " The narrative is simple and manly and full of the freedom of forests. . . . This 
 record of his work ought to awaken the interest of the generation growing up, if only 
 by the contrast of his active experience of the resources of Nature and of savage life 
 with the background of culture and the environment of educational advantages that 
 are being rapidly formed for the students of the United States. Prof. Dyche seems, 
 from this account of him, to have thought no personal hardship or exertion wasted in 
 his attempt to collect facts, that the naturalist of the future may be provided with com- 
 plete and verified ideas as to species which will soon be extinct. This is good work 
 work that we need and that posterity will recognize with gratitude. The illustrations 
 of the book are interesting, and the type is clear." Neva York Times. 
 
 " The adventures are simply told, but some of them are thrilling of necessity, how- 
 ever modestly the narrator does his work. Prof. Dyche has had about as many expe- 
 riences in the way of hunting for science as fall to the lot of the most fortunate, and 
 this recountal of them is most interesting. The camps from which he worked ranged 
 from the Lake of the Woods to Arizona, and northwest to British Columbia, and in 
 every region he was successful in securing rare specimens for his museum." Chicago 
 Times. 
 
 " The literary construction is refreshing. The reader is carried into the midst of 
 the very scenes of which the author tells, not by elaborateness of description but by the 
 directness and vividness of every sentence, He is given no opportunity to abandon 
 the companions with which the book h^is provided him, for incident is made to follow 
 incident with no intervening literary padding. In fact, the book is all action." Kansas 
 City Journal. 
 
 "As an outdoor book of camping and hunting this book possesses a timely 
 interest, but it also has the merit of scientific exactness in the descriptions of the 
 habits, peculiarities, and haunts of wild animals." Philadelphia Press. 
 
 "But what is most important of all in a narrative of this kind for it seems to us 
 that 'Camp-Fires of a Naturalist' was written first of all for entertainment these 
 notes neidier have been ' dressed up ' and their accuracy thereby impaired, nor yet re- 
 tailed in a dry and statistical manner. The book, in a word, is a plain narrative o' 
 adventures among the larger American animals." Philadelphia Bulletin. 
 
 " We recommend it most heartily to old and young alike, and suggest it as a beauti- 
 ful souvenir volume for those who have seen the wonderful display of mounted animals 
 at the World's Fair." Topeka Capital. 
 
 New York : D. APPLETON & CO., I, 3, & 5 Bond Street. 
 
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