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I *' 'T^WO systems of ventilation so far appear to have been ■'• adopted, viz., the upward or the downward exhaust. The fundamental principles of ventilation are : 1st. Heated air is relatively lighter than coldei air, and will continue to ascend and the cold air to descend so lon^ as they are fiee to move. 2nd. More or less than a given quantity of air practically con- sidered cannot occupy an apartment and cannot be introduced unless an ec|ual quantity be withdrawn, or withdrawn unless an equal quantity be introduced. These two simple and self-evident propositions will explain nearly all the phenomena observable in ventilation. The first method adopted by engineers and architects to give movement to air for the ventilation of mmes and buildmgs was to heat an upflowing column, thus lessening its specific gravity and causing it to rise with corresponding force. That system was employed in the British Houses of Parliament, where in many of its towers a charcoal fire was kept burning and thus a force obtained to propel the air through the building. It has been practically demonstrated, however, that one pound of coal burned in the furnace of a steam boiler to drive a fan blower will generate as much force and consequently is capable of producing as strong a current of air as 38 pounds expended in heating a column of air to act by its diminished gruvity If heated air is introduced into an apaitment containing air at a lower temperature through registers at the floor, it rises rapidly to the ceiling, and if there are openings at the ceiling it escapes without (except in a very slight degree) mixing with the air in the apartment. The air that passes ofif in this manner is absolutely lost and the heat •imparted to it wasted. It does not remove the vitiated air con- tained in the lower part of the apartment, it does not form with it a homogeneous mixture and does not communicate to it more than a small portion of its heat. But if, instead of escape openings at the ceiling they are placed at the floor, the phenomena observed will be widely different. The heated air will as before lise to the ceiling, but instead of escaping, will press the colder Jiir downward to the exit ducts and fill the apartment with pure warm air ; the air vitiated by breathing will at once sink below the level of the mouth .ind in & few seconds will be carried off, no accumulation of foul air being possible. Various opinions are given as to the amount of fresh air necessary to render the products of transpiration and respiration i ■-, I innocuous. These estimates made by distinguished observers vary from 2 to 50 cubic feet per minute. liilMa*«ilMMtlaiiiand are generally based upon the hypothesis that the fresh air introduced into an apartment mixes uniformly and homogeneously with the vitiated air and dilutes it to an extent to render it innocuous ; but if mstead of mixing with the air of the apartment, the warm Eure fiir should rise to the ceiling and escape, all conclusions ased on the hypothesis of homogeneous mixture would be fal- lacious. If the air that has once been respired could be imme- diately removed without being the second time taken into the lungs, it is obvious that so far as respiration is concerned no more need be introduced into an apartment than can be breathed ; this amount is easily calculated. At a temperature of from 65 to 70° Fahrenheit the followmg average results are given by Dr. Wetherill for the respiration of an r'''ilt : Number of respirations per minute, 20 ; cubic inches of air iiihaled at each respiration, 20 ; cubic inches per minute, 400. The carbonic acid exhaled is stated to be 15 cubic inches per minute, and the surrounding air vitiated is 2% cubic feet per minute. Four hundred cubic inches is less than one fourth of a cubic foot and this is all that can be taken into the lungs per minute. The House of Representatives at Washington is provided with 60 cubic feet per man per minute, and yet the vitiated air is not removed. The quantity of air introduced is twenty times as great as the quantity that could be vitiated by respiration provided there was a homogeneous mixture. The facts which are daily observed prove that such a homogeneous mixture does not exist under the present system. If nmeteen-twentieths of the heated ^ir which enters the apartment escapes without being utilized, it follows that nearly all the fuel consumed in heating it has been wasted. In the process of respiration 15 cubic inches of carbonic acid per man per minute are ejected from the lungs. This gas in course of time would diffuse itself throughout the apartment, but it IS well known that its density is so great that it can be poured from one vessel into another, or if poured into an inclined trough it will flow downwards, extinguishing successively a row of lights. The specific gravity of this gas is 1.52 or 52 per cent, heavier than air. Its tendency would therefore be when exhaled to sink below the level of the mouth and occupy the lower portions of .an apartment near the floor, but it has been supposed that the elevated temperature at which it is projected from the lungs causes this gas tc rise and escape at the roof ; the fallacy of such an opinion can, however, be readily proved. Even if the temperature at which carbonic acid escapes from the lungs should be so elevated as to render it momentarily lighter than the surrounding air, it would soon part with the excess of heat and then seek the level due to its superior density — but in fact under the condition of things which actually exists there is only 20° difference in temperature betw en the air when first expelled from the lungs and tnat of the apartment. As air inci-eases in ^ , volume 1-460 of its bulk for each degree of Fahrenheit, the effect of increasing the temperature 20° would be to reduce the specific gravity less than ten per cent., and *he carbonic acid upon leaving the lungs would still be 40 per cent, heavier than the air of the apartment. It would seem impossible for this dense gas to rise to the ceiling and escape at that level without a violation of the laws of pneumatics, unless by powerful me- chanical means. Dr. Wetherill reports that each flame of gas consumes as much oxygen and gives out as much carbonic acid as five human beings. General Morin reported that a ventilation of i^}4 cubic feet per man per minute principally downward left no percep- tible odor in a lecture room, while the upward ventilation of the Halls of Congress with 60 cubic feet per minute, is notoriously defective. As regards the direction the products of respiration take after leaving the body, the evidence in support of the tendency to rise is from a report from the Smithsonian Institution ; its author seems to have smoked a pipe at the Institute and the smoke ascended — but the objection to this experiment is that tobacco smoke is not one of the ordinary products of respiration. The expeiiment does not prove that the gray smoke which was seen to rise was carbonic acid. The experimenter does not state in what direction were the ventilating currents in the apartment or bow produced, and there was nothing in the experiment to prove t..at with a gentle downw.'ird ventilation the smoke would not have moved downward instead of upward — in fact it proved nothing at all in reference to the direction of the products of respiration. Lewis L. Leeds quite agrees with General Herm.m Haupt in conclusions both as to theory and the necessity for putting in practise a system of exhaust for ventilation from the floors of the house, and says very extensive practise and close observation for many years past have fully convinced him that the human breath, which is the great source of contamination tends first towards the floor in a still room of 70°, and that there is a probability in a closely occupied room that there will be quite an excess in the accumulation there. This applies to rooms warmed exclusively by heated air. The contrary opmion — that is the assumption that the breath and the impuri- ties exhaled from the body rise to the ceiling and accumulate there — was advocated strongly in the ventilation of the English House of Parliament, and it is reported that some two or three millions of dollars were spent in endeavoring to heat and venti- late that building comfortably, and as the proceedings in regard thereto were spread over the world to an extent probably one hundred times greater than any previous publication or action in regard to ventilation of any public building, that theory of venti- lation became strongly impressed upon the public mind as being the correct one. I consider that idea erroneous, hence all theo- ries of ventilation based upon it are consequently wrong. In the : majority of our rooms the heated air entering (which, of course, must assume to be pute air) does not enter warmer than the con- tained air one half of the time and probably not mote than one quarter of the time. Mr. Leeds goes on to advocate an open fire and further states — " 1 believe it would be at all times and under all circumstances very desirable to have a large amount of the air drawn from the floor as nearly as possible under or near each member's seat, and also from under the seats of all the benches m the galleries, but to know how or when and how much to draw from the ceiling would be a much more difficult question to decide. That there should be such openings we know from everyday experience, the necessity for opening doors or lower- ing external windows to relieve the upper part of a room when it gets too warm. The openings at or near the ceilings require to be closed or opened according to the varying conditions of the room. Heat applied within any building causes movements of the air with more or less loice according to the difference of temperature of the external and internal atmosphere. The ex- ternal wind is a source of considerable power. It is important in the application of power, either to make it conform to and co- operate with the natural forces vind merely assist their action, or otherwise make it of sufficient power to entirely overcome all these natural forces — if much care is not exercised in the adjust- ment of these forces one just counterbalances the other and stagnation is the result. Scientific and medical authorities gen- erally concur in the opinion that in-door air after heating should contain nearly the same proportion of moisture as the average of out-door air of the same temperature, but when air is brought in from out of doors at a temperature of zero and raised by heat- ers to 68°, it would require the addition of 4.343 grains of water per cubic foot of air to bring it up to the required degree of moisture. For the proper moistening then of fresh, warmed air introduced at the r.ate of 20 cubic feet a minute for each one of three hundred persons two hours, the air taken at zero and at an average degree of moisture, no less than fifty-ijne gallons of water would be required to be added. Exactly how much vapor or what per cent, of moisture is the most healthy has not yet been determined. From much observation we have taken 65 per cent, of saturation as the amount most likely to prove healthy — the mean relative humidity of the air at Philadelphia for the year 1863 was 57.2, and the mean average for twelve years, 68.5. Dr. Wetherill in his report on ventilation of the Capitol at Washmgton says : "Hood, (" Warming and Ventilation,") esti- mates the air required for ventilation by the amount needed to take up the moisture from the skin and lungs. The air required for respiration (/. e. oxidation) is very much less than that iieed- ed to hold in solution the vapor of the skin and lungs, which evolve 12 grains of water per minute. If the temperature of a room be at 60° with a dew point of 45°, a cubic foot of air will absorb 2% grains of vapor, or, in other words, the perspiration from the body will saturate 5X cubic feet \ H 'f ^ f> I s of air per minute. If, however, we take the dew point lower, say not to exceed 20° or 24°, then 3X cubic feet of air per minute will be required to carry off the insensible perspiration, while, for the pulmonary supply one-fourth of a cubic foot will be need- ed, making a total of 4 cubic feet. In summer, as the dew point is higher, more air will be needed, viz., 5 cubic feet p«,r mmute for summer ventilation. In a foot note to the above it is stated that Seguin gives the exhalation of water from the lungs, 7 grains, from the skin, ii grains, total grains, 18 per minute. If the dew point is maintained uniformly at 52° the following is the calcula- tion of quantity exact for this case : A cubic foot of air at a tem- perature of 65° with the dew point at 52° will absorb 2}4 grains of vapor, and if we take the mean of the two authorities above cited regarding the quantity exhaled by each person, we will have 15 grains per minute, and to absorb this under the above conditions will require 6 cubic feet of air. Add to this the one- fourth cubic foot required for breathing, and we have 6)4 cubic feet as the total amount vitiated per minute. The surface of an average man is about 18 square feet. If, therefore, we imagine such a man walking in the pure open air at the rate of two miles an hour on a perfectly calm day the air will be flowing past him at the rate of 176 feet per minute, and as he is one foot deep from front to back, the average thickness of the envelope of vitiated air which surrounds him may be found as follows : Let A=The quantity of vitiated air per minute in cubic feet. . 6^ B=The surface of the person in square feet 18 C=The extent of the person in direction of the current of air in feet I D = The velocity of the current in feet per minute 176 X=Thickiiess of envelope in inches Then la A C. = X BD and X = 0.018 or 1/55 of an inch. In supplying air for the upward ventilation of a hall containing an assemblage of people, however, it is absolutely essential that the direction of the current should be vertical, otherwise that which has been vitiated by one person would be given toano'.her to breathe and perspire into. If we now assume a man stand- ing upright of the average height of 5' 6", and the velocity of the current at 5 feet per minute, we will have for the value of the terms in above formula : A = 6X ; B=i8; C = s% D = 5; where- upon X = 4.i6 inches. If this envelope of 4" thickness be drawn upward, it is clear that the nose and mouth will be always supplied entirely with vitiated air, no matter how pure it may be one foot away, while if it is drawn downward those organs will always be supplied with perfectly pure air. This consideration alone is quite suffi- cient to determine in favor of downwanl direction ; there are, however, some other advantages in the downward over the up- ward direction. The temperature of the human body varies 2" either way from 98°, a sudden variation of 5° or 6" being said to be fatal. If, therefore, the air is supplied at a temperature of i 65°, it will be 32* cooler than the body. With a downward cur- rent the head will be in this cool air while the feet will be in- closed in an atmosphere nearly if not quite as warm as the blood wiihin then , and to "keep the head cool and the feet warm " is one of the fundamental rules of hygiene as well as of comfort. A current of air coming up through the floor will always bring along with it the fine dust which the greatest care cannot pre- vent accumulating there to an extent which renders it unplea- santly sensible in all assemblages supplied with an upward ven- tilation. With the downward ventilation it is only necessary that the dust shall be thoroughly removed from the inflowing air at the mouth of the inlet duct to maintain the hall perfectly free from dust. Again, with upward ventilation the entire hall is filled with viti- ated air, the vitiation having taken place near the point of ad- mission, while with the downward ventilatioii the ventilation takes place near the point of exit .ind the whole upper part is full of pure air. In a hall say, 36 feet from floor to ceiling, and the fresh air is admitted through apertures well distributed in the ceiling — it has thirty feet to move before it comes in contact with the heads of persons on the floor. During this movement all eddying currents induced by the increased velocity with which it is necessary that it shall piss through the apertures have be- come quiet, and the whole mass descends with an uniformity im- possible to obtain in the vicinity of persons ventilated with up- ward ventilation, and one of the most important considerations to be kept in view in ventilating an apartment is to avoid per- ceptible draughts. Mr. Goldsworthy Gurney, in his examination before a Committee of House of Lords, said : " We have found the down current always more agreeable ; the up current is some- times used, but it is not so pleasin;:^ and not so eflfectual." One objection used against the downward system is that it is against nature to force air downward. Although this opinion is entertained by an extremely large numljer of otherwise well-in- formed persons, every engineer of ordinary attainments knows perfectly well that it is as easy to force air in one direction as another. Another objection is, thai as air is additionally warmed at the same time it is vitiated, that which is vitiated and warmed has a tendency to rise whatever may be the direction of the gen- eral mass surrounding it. This is true, but this tendency is so feeble that its opposition to a current of 5 feet per minute would not be perceptible. It has been shown that with a vertical cur- rent of 5 feet per minute the mean thickness of the envelope of vitiated air surrounding a man of the average size when stand- ing is 4", this more than two hundred times as thick as when he is walking at the rate of 2 miles an hour in a perfect calm. As, however, the air has to be brought from such a direction that mouth and nose are always supplied with air of absolute purity, to insure the control of its direction by mechanical means, a cur- rent of 5 feet per minute has been assumed for the minimum .velocity to be given. When the weather is fine, or in other words, when the outer : \ A air from which the supply is derived is in the desired condition as regard temperature and moisture, and no expenditure is re- quired upon its conditions, then a maximum amount may be given, the minimum being employed when its condition as re- gards temperature and moisture has to be changed to the great- est extent. The only limit to the amount of air it will be advan- taj^eous to supply is that fixed by the rule that the currents past the person must not be sufficiently rapid to become sensible. Some persons are sensible to currents of much less velocity than required to render others conscious of them. Most people ^ can feel a current having a velocity of 150 feet per minute, very few can perceive one of 90 feet per minute. To be quite sure , that no one, however delicate, should be conscious of being in a current, the maximum current would be safe at 50 feet per min- ute. But 10 feet per minute will give a bountiful fresh ventila- tion. The average thickness of the vitiated envelope will then be two inches, or one hundred times thicker than when walking out doors in a calm. With downward ventilation, however, the nostrils are in pure air equally as when walking, the vitiated air enveloping the lower part of the person only, leaving him uncon- scious of its presence. Even when the weather is good and the temperature of the air deliglithil and the wind blowing with the most desirable force, an open window in the side of a great hall filled with an as- semblage of people would furnish air to those furthest from the window filled with emanations of all the persons it has passed on its way. That the air as vitiated has a tendency to rise has been a fav- vorite theory among scientific men. Mr. Gurnev was one of the first to stoutly deny the fact in his testimony before Committees of Parliament ; he asserted that the downward propulsion which the breath received by the position and direction of the nostrils did not cease so far as the impurities with which it is laden are concerned, till it deposited them on the ground, also that on a frosty day the vapor from a person's mouth may be seen to de- scribe a parabolic curve to the ground. But any one may see : the vapor of the breath driven from the nostrils taking at first a downward course ; a breath of a fair strength, with the thermo- meter near freezing point, may be seen by its condensed vapor driven downward and slightly outward for a foot or more. In this observation, a wind wheel (in air of 26" Fahrenheit), moved rapidly near the body, and steadily at a distance of six mches in front and also at two feet above the head. Notwith- standing this upward current, the breath was strongly marked by condensed moisture fourteen inches below the nostrils, and, would doubtless have been seen further down but for the dissipa- tion of the moisture. In a room with the air at 65° the same wind wheel was in mo- tion close to the vital parts of the body, but stopped entirely at two or three inches distance from the body or above the head — this was anticipated, because the force that curries the wheel is the rising of the air in consequence of its greater heat and light- : I I 8 ness than that of the surrounding air, and is proportioned to the difference of temperature. In order to determine the amount of heat operatinjf to cause the air to rise, a thermometer was placed within the clothing near the vital parts of the body, where it was found to stand at 82°, while the person remained in air at 65°. On going into air at 20° with additional clothing, the thermo- meter stood at 76°. The air around the body in a warm room, therefore, would rise with a force not far from 17°, while in the outer air at 20° it would rise with a force not far from 56°. Prob- ably the air would rise with a velocity somewhat less than these figures, but relatively they are nearly correct. A more sensitive instrument would have been affected at a greater distance, but the same wheel showed a distinct downward motion of the breath 15 inches below the nostrils in opposition to all the rising ten- dency by reason of the warmth of the breath and air about the body, aud this motion would have been shown at a greater dis- tance by a more sensitive wheel. Let us now suppose, to be well within bounds, the breath to be moved 12 inches below the face, the downward motion having ceased, the upward motion should then begin, which is to carry the breath up out of the way. This old breath has about one second in which to rise from rest or reverse motion, more than 12" in order to be out of the way of the next inhalation. The difference of temperature necessary to give this movement of 12 inches in the first tecond, if the breath rises by heat alone, will surprise anyone not familiar with such calculations, it is not less than 180°, that is to say, the breath in order to start from rest and rise 12" in one second through air at 65°, would ha/e to be at a temperature of 245°. The absurdity to which this calculation and experiment re- duce the idea that our breath is carried away from the face by its upward tendency from heat, is increased by the observations which every one may make, that a thermometer at 65° cannot be raised more than one degree by breathing upon it at 9" distance, and that at 10" no effect can be perceived. Under the most fav- orable circumstances all causes combined are not sufficient to carry the expired breath up out of the way before another inhal- ation, as may be seen on a frosty day, and it is evident that the air contaminated by the body, if carried upward must be inhaled. We will consider the circumstances of a large hall of assembly and show the operation of the two systems. Suppose a floor well packed with people at the bottom of a cubical or hemispherical hall : suppose them to have entered at once, the hall bemg pre- viously filled with pure air ; directly the lower stratum of air in which is the audience, becomes contaminated by their exhalations and emanations. Now the problem is to get '.hat stratum of air out of the hall before any of it can come into use again, and to replace it with fresh air of the right temperature. It is obvious that it cannot be taken out sideways, because then many would have to breathe over again the breath of others — it can be taken only either up or down. If taken up, the fresh air that is to supply its place must enter at «he floor from which ( ' the foul air rises, for no air will leave the spot till other air is ready to fill its place. In order to lift the whole of the foul air bodily froui the floor, it is necessary that the whole floor should be open for the admission of fresh air. Wherever there is a piece of solid floor through which the air cannot pass, there will be a dead space of foul air above it which will not rise with the rest, but will remain to be gradually mixed with the fresh air enter- ing around it. If the dead space is considerable, iV ^ whole amount of air required must enter in the limited space of the openings, and the velocity must be propoitionately increased. According as the space is reduced and the velocity increased, the air entering has a force that carries it up beyond the place where . it is to be used, and mixes it with the foul air passing off, a part of which mixture will return in counter currents n.id gradually replace the air in dead spaces. Dr. Reid, of the House of Commons, England, the most scien- tific and experienced, perhaps, of the advocates of the upward system, seeing this necessity for introducing- the fresh air through the whole extent of the floor, had the entire floor made of perfor- ated iron. This was afterwards covered with hair-cloth carpet- ing, and through nearly its whole exte.it the fresh air was admit- ted. The result was, that on account of the rising of dust by the entering air, and still more on account of the uncomfortable draughts brought up against the members' legs, nine-tenths of the floor was covered with sheet lead under thecarpet. When the entrance for fresh air was thus limited complaints became so loud both of strong currents and of foulness of air, that the whole matter of ventilation was turned over to Mr. Golds worthy Gur- ney, who undertook it on the opposite system of introducing fresh air above and taking out the foul air at the floor. It IS very important in the warming and ventilating that the pure air to be supplied should be of the same degree of tempera- ture and the same amount of moisture as that of an open space m a pleasant time in summer. With respect to the actual degree of ventilation necessary for health there is great difference of opinion. The following vol- umes of air in cubic feet per person and minute have been as- signed by different experimenters : Dr. Arnot, 2 to 3 ; Tredgold, 4; Mr. Toynbee, 10; Dr. Bell, 10 to 25; Peclet, according to circumstances, 10 to 20 ; Peclet, at least 5 ; Roscoe, (insuffi- cient in Burracks), 10 ; Roscoe requires at least 20 ; Dr. Reid, minimum, 10 ; Dr. Reid requires according to circumstances, 20 to 60 ; Vierordt, 2}4 ', Hood, ("Warming and Ventilating") es- timates the air required for ventilation by the amount needed to take up the moisture from the skin and lungs. The air required lor respiration (/. e. oxidation) is very much less than that need- ed tohold in solution the vapor of the skin and lungs which evolve 12 grains of water per minute. If the temperature of the room be at 60° with a dew point at 45°, a cubic foot of air will absorb 2)4 grains of vapor, or in other words, the perspiration from the body will saturate 5X cubic feet of air per minute. If, however, we take the dew point down say not to exceed 20° to 24°, then lO 3X cubic feet of air per minute will be required to carry off the insensible perspiration, while for pulmonary supplies % cubic foot will be needed, making a total of 4 cubic feet. In summer the dew point is higher, more air will be required, viz., 5 cubic feet per minute for summer ventilation. Professor Miles in his report on ventilation of houses and schools assumes that if the temperature of the air ranges from 65° to 70 degrees Fahrenheit, we have the following average re- sults from the respiration of an adult : number of respirations per minute 20 ; cubic inches of air inhaled and respired 20 ; cubic inches of air inh?led per minute 40c ; cubic inches of oxjgen each respiratioTi 4 ; cubic inches oxygen each minute 80 ; pro ducts respired : r. damaged atmosphere with nitrogen in excess ; 2. fifteen cubic inches of carbonic acid gas ; 3. three grains of vapor of water. The surrounding air is vitiated by the mixture of the products of respiration with it at the rate of 2% cubic feei per minute. The total average loss by the lungs and skin in twenty-four hours is almost 2% pounds of water, of which somewhat more, % say 2>^, are furnished by the skin, of these 2% pounds (only 1/6) is furnished by the vital process of secretion by the sweat ^ glands, for the greater part of the moisture transudes through the skm by simple evaporation. Fot health the body must evapor- ate a quantity of water within certain limits; the amount evapor- ated is influenced by the hygrometric condition of the air and by the state of the body itself. The evaporation is increased by muscular action and by a dry atmosphere, it is diminished by re- pose and by a moist air. EXTRACT FROM THE REPORT OF A SELECT COMMITTEE ON THE VENTILATION OF THE HOUSE OF COMMONS, LONDON, PRINTED MAY 3 1 ST, 1 886. " The plan adopted and w orked for many years under the superintendence of Dr. Percy consisted in drawing the fresh air into the House and the vitiated air from the House by means of heated shafts in the clock tower and in Victoria tower. By this exhaust process the air in the House was placed under a some- what lower pressure than the air outside, and a pull thus created which caused the entry of foul air from any accidental source of impurity within reach of this pull, as from closets, etc. Since this plan was established many years ago much progress has been made in the art and science of ventilation, especially in me- chanical appliances for the purpose, and by means of these, greater efficiency and certainty, as well as increased economy in working was attained than was possible under the elder system. The great advantage of mechanical ventilation is that as the air is pumped m, a slight excess of pressure exists m the venti- , -t.' lated spaces over that in the outside, and therefore any aea i i oi » z^^-^*^ of air from impure sources, such as imperfect soil pipes, closets, etc., is avoided. The Committee, for the above reasons, are of opinion it is advisable to cut off the exhaust so that the air pres- sure may be above rather than below that of the external atmos- i' .,j3iiih 'I'^livx:.:^".?!^!^'. J ^*v phere." But it appears by evidence given before the Select Committee of the House of Commons on ventilation, June 1891, that the recommendation in the previous reports had only been carried out to a limited extent, and that the system of extracting the vitiated air at the ceiling is still in operation — the witness stated that air drawn from the Court Yard passes by steam batteries by which it is warmed — it then passes down the floor of the house which is perforated all down the centre and in various other parts, there U ascends through the ceiling and passes down four shafts about 700 feet in length to the basement and then horizontally through the basement for a considerable distance and discharges into the Clock Tower where there is a very powerful up cast, which must require a very much larger consumption of fuel than would be necessary if the exhaust were from the floor of the House by mechanical means. POSITION OF HALLS. Some adverse criticisms having been made with respect to the House of Representatives at Washington being surrounded by rooms, and not having any contact at the sides with the external air. In a report to Congress the objection is thus met, " It is sup- posed by many that the inclosure of one building within another, the inner one being the hall, is a serious defect m the construc- tion with a view to equable temperature and a healthy ventilation ; on the contrary, it is a great advantage. If the hall approached the exterior wall it would be subject not only to all the internal changes of temperature and elements disturbing the ventilation, but also to all those of the external atmosphere and the weather. Almost every one of the disturbing elements that have been named would be greatly aggravated if the hall approached the exterior. External influences like those of noises, winds, and storms would make themselves felt disagreeably which are now altogether excluded. There is no doubt that the more perfect the ventilation is the more periect the acoustic properties of the hall will be. A pure atmosphere being favorable to the speaker's health and strength, will give him greater power of voice and endurance, thus indirectly improving the hearing by strengthen- ing the source of sound, and also enabling the hearer to give his attention for r. longer period. In compiling the foregoing remarks, the various reports to Congress by A. C. Stimers, Naval Engineer, General Haupt, L. W. Leeds, Capt. Meigs, E. Clark and others, have been freely quoted, also reports of Select Committee on Ventilation of the House of Commons, London. After many years of study and experience I am strongly of opinion that the most efficient system of ventilation for halls for the assemblage of large numbers of people is by the Introduction of fresh, pure air heated by passing over steam or hot water pipes in chambers and driven and exhausted by the most approved ap- Eliances, introducing the pure fresh air at the ceiling and ex- austing at the floor, which may be termed the downwards draught and plenum system. ! i I iHiir ""-'"'