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Read before (he Astronomical Section of the Hamilton Scientific Association, April 29th, 1902. BY H. B. WITTON. Except the sun iisclf, none of the heavenly bodies has attracted so much attention as ilie moon. Her apparent size and nearness to the earth, the subdued splendor of her Hght, her erratic course in the heavens, the r.ipid change and frequent recurrence of her phases, and the weird effect of her eclipses, have made h "• moon, from time immemorial, an object of intense interest. Literal j*-;, ancient and modern, bears witness to the truth of this. The Vaidie hymns shew that in the e.irly dawn of Indogermanic civi'ization the phases of the mnon were i)ersonified, and her influence was invoked with solemn rites. In many languages her name is f^iven to one of the daji of the week ; this indicates how long she has !)een held in veneration, as Laplace has shewn names of the week-days are among the most ancient monuments of astronomical knowledge. Poetry, too, has thrown ocr the earth's satellite graceful veils of myth and fancy; while the most prosaic utilitarianism, in the interests of commerce, has been fain to do her honor. I'ythagorus, in his system of cosmic harmony, credits the moon with contributing the highest note to the music of the spheres ; and our own less imaginative forefathers, by such names as lunar caustic, selenite — thought to be moon-froth — and lunatic, have left a legacy to our vocabulary shewing their faith in the potency of the moon's inlluence. In these latter days, that peculiar veneration the moon fortnerly commanded no longer obtains. The age of faith in her occult powers expired with the astrologer and alchymist, to be succeeded by an age of intjuiry and knowledge which, rejecting the superstition of the old learning, still cherishes some measure of its devotion. Though we no longer plant and sow, herd our cattle, prune our vines, and gather in our harvests in awe of her sovereignty, yet our lunar tal.les, nau,,^, j, have overthrown nun.berless anc en/. "'' '"""'^'^ ^^''^ moon did not utterly perish Iv^Zk T"""' ''""''""" '"' 'he spirit Mill lives. tranJfoL d into '" r "■^;'""-'-'. ""' ■" ---.ves,i«ationo.herS;^-'l::----~^ -Mir::^.;:rntr::t t::rr .r --,----0 cannot choose but read and be inl ! , """' '"""' "''»'^"" ^'ation, both sun and n,oo„ a e "t """" ""^ ^""■^ -- "est none can fail ,o notice In "hh V ' ' """'"" ^">'" "»' 'o toward the west, co„„„on t" al he h ,'° "" ''"''■^^•-■"' "«"-" •he s.ar.sphore wi„ shew ZLT'r,7Z' """'' '^""'''""" "' among the stars toward the ea, H ' 17" "'°''"'' ™ " ^"""-^ '" d'rection, is otherwise different 1'^ '"T"' ""'"«'' '""'"" moves eastward about m decreed .^ '', "'"''"""'" ""^ '"""" heaven, in . ,.,o„,h ^iSf,^';"^' "-l '""^ ''" ""^ "^ "- darkpartsofthedislcaLtottth H IT"" '"'^ ''"S''' and diately before conceal^entTh L ' •"' °' f ''^'""<^"' ' "'"e cent having its |i„,(, ,„„„<, the east anH", ."' " ^'^'="^'' "- to the beholder's right hand Wh"n h ,f^ ^°'" ""'' "^™'"'"^^ ^ the moon in opposi ion become! ^ul n ."°"'"^ ^""^'^ '^ '""- -^ A«^ the dark part of the disk 2Zl h ^™™ ""' '" f"" moon I / full moon till the wanintr cl^^' ^^""l '"""""="-d, and from I the illuminated part of thTd !k I '" "'' ^'''^ °' "^^ ^""hght I becomes obscured '''' '"'"°^' 'mperccptible degree II In going through these phases the moon more than completes the circuit of her orbit around the earili, for the eartii during a Uma- tion is carried forward in its movement' around the sun about 30 degrees, and the moon must pass over that distance before sun, moon and earth tnke the relative positions recjuisite to make new moon. Such a lunation, or course of the moon once round the earth, and far enough on a second course to t ome again in conjunction with the sun, is called the moon's synodical revolution, ['he mean lime for making it is 29 days, ij hours, .(4 minutes and 3 seconds. The mean time it takes for the circuit of her own orbit only is but 27 days, 7 hours, 43 minutes and 1 1 seconds. Thus in each lunation the moon, from the earth's motion of translation round the sun, proceeds 2 days, 5 hours and 52 seconds on a second course before coming into the nccess,iry alignment with sun and earth essential to present the phenomenon of new moon. These figures furnish the mean time in which the moon is carried through her orbit, but disturbing forces so considerably affect her velocity and direction, that astrono- mers, only by long profound research, have succeeded in foretelling what will be the moon's place in the heavens at any given future time. Astronomical science regards the heavenly bodies in two aspects : in their relations to time and space, and as masses of matter moving m obedience to cosmic? I forces. .Ages of observation prepared the way for the latter conception, and ancient astronomy chiefly kept watch over the times and seasons. Still, in the early stages of astro- nomical research, the moon was accorded attention, as many ancient nations used the moon's pliases as a measure of time. The word moon, it is thought by some philologists, can be trace.! to the root w/d, meaning to measure. Although a lunation is, in many respects, a desirable standard for measuring time, ic has been found extremely ditificult to make it a sub-division of the tropical year or the time taken by the earth to complete her course from, and return to, the vernal ecjuinox. Where- ever the lunisolar year has been adopted intercalations have been necessary to bring the 1 aar months and solar years out even. The Greeks used simultaneously the two standards, and had no end of difficulty to keep them from overlapping. Their Olympiads supply a record for a thousand years, and are perhaps the best scale of past events on record. They originated from holding, every four years, such corrtcional device., .l,e c,cl" , N ^ '•"' ''""*" "^ years, , of wh.ch had .^^n:::f;.:!Z;:ZT'"""'"' had .. da,s ..cH, andtu:- :::*;:;;:' ::^,r "'7 rT^' between the tha. ,>,„des of r...k«n,„« tn , h ,ro lal ' T'*"' dar month, and lunations. This c,He ,', u ' '■"' '^'^"■ because, it is said the Aih .„ ""^ «"'''™ ""'"I'", s.i" used to dr:;;,::: "^::::z:'t " '; "«"^" °^ ^""'' ^^ has decreed the Sunday follow, n,.;"' ^V"'"'^-^!'^" ■"'■•'-''>■ equinox shall he observed asl', < '™"'' '"" ""= ^■^•""' don, and ancient H«::'l h ^^ed l,!::""'^^^" ^^^-- cator of .he precise ,in,e.,r ho,d,n,,,;::':l;'L;;r "'^"'"^■• ™oti::^rlr^::::r;:^\:l::i:-:^''■-"-"■^ motion accords ,iih an.l l,„i II n ^'""'^'"^^'^ '" '^liewinK that -ience. The reasini. ^ „': .'r:! "f "^'"^""- "^ '^- confessedly intricate and i„ ""''"""'""^^i -c.en.x' depends is thede.otiLofa";;::' ''v :xtsr::r^ ™^ '"" ^"""'='^«'^ or training to comprehend ,h„. t . i nkTirZ"" 'C^'^"' ''"'' conc-ption of Copernicus that the ear.Vir J t ■'"""'" ^ "'" -d an annual translation aro.Ind h^ a^d^ Se "'^T' ""T a planet's orbit is an ellinse -hn,,, ;,c ' " ''"" ">'" areas swept l,y the radius /r ''"""' ^ "' ' •""''"' "'■■" 'he time of it'n,otio, nd th at e' ' "'? "'^ ■-"■-'-••"e to the are proportionate ;o"lfe cub of .r^'V""""" "'"" "^ '^'*"«'» - these the '^^J: T;:::^^"j^T:r^zt: ''"\ '"' bod.es attract each other dircrilv as thin ' "'^' "" squares of their distance fron ac oth an^ t^ h"""\''^' "'^ ''^ on Which the Whole structure of .nodtr'a • „ ,:;r,,:, u "k '"^ ler s generahzattons nere epoch.n.aking. They com, II a '" adm,ra.,on that they were conceived in^s.roi:kTtin;es:'an: 'r I i s mixed up with aitmU gical fancies. Hut Kepler, even in entr, erred lilte a man of geniu*. When hij fed in.jk the wrong path, hi> 'ice often turned tiiward the right. He lihend the sun to h.ive a soul, which w.i« constantly rotating, lie also thought that betwien sun and planets there is a friendly side, lUid a side that is hostile ; and that when the friendly side »-as turned 'Sc planets movt:d toward the sun, and when the hosiile side was turn^^^d ti.ey moved from him. All this was lam iiul enough, but here .rro: pointed m the direc- tion of truth, for twenly years later C.ilileo saw Ihiough his telesnipe that the sun's rotation w.is a reality. Newton's theory ha^ withstuo 1 more than two centuries of critic ism, and is confirmed by the most carelul observations. Kinlit thousand telescopic observation! taken of the moon during a period of eighty years were compared, under direction of I'rof. .Viry, with the place at which, by Newton's theory, the moon should be :it the time of each observation. Kach theoret ical place was computed sc,.arately and independently. The woik took a body of calculators eight years, at a cost of X4>3oo, and by it the truth of .Newton's theory was fully sustained. If the moon revolved around the earth, controlled solely by force of their mutual atlr.iction, the calculation of her orbital motion would present no spec: ilticulty to the expeit astronomer. What would be the moon's pos. ion in the heavens at a given future time could be predicted with like exactness to tH..t of Jupiter, which has been given ten years in advance, to wiibin half a second of actual observation. Itut in addition lo attraction of the earth, the moon is influenced by that of the sun, and to a less extent by that of the nearest planets. Moreover, from the moon's elliptic orbit and incli- nation of the plane of that orbit to the plane of the ecliptic, the sun's attraction is a force constantly varyinj.- both in degree and direction. Hence calculation of the lunar motion is one of the most difficult tasks accomplished in the field of physical aslron:< ny. In a letter to I'lamsteed, .Newton himself lets fall words bord-^ring on doubt as to whether he should finish the task. These lunar inefpialities, as they are called, Prof .Airy explains in his work on " (Iravltation." His book was written for general readers ; and Lord lirougham, who tried his hand at simila' woik, deemed it the best account of the Newtonian philosophy ever written, or likely to be written. liesides theoretical interest of being able to predict exactly the ,To'f' h"?,;;' ""' '"■ ^"" "' "">• ""-' ""-. toward ,„c. Ia„er use a. sea. Whrwr, ,H "'', * *'"''''■■■ '■"""«'' '°' ''^'"'"' -aculifl-rrencein ::,:'::'•,:"'' "",*"" ^'"' *'' '"""' '''^ -o p,;::::jc :;;" "^.^rr r . ■'- "'-' "'^' """-"^ .he e«c. angular dC^^t T r",!:! ™"'?h''"' "'""''''" •iome of the principal stJ lu ! ' ''" "" '"""" ^'"^^ as at his observation ^ " ''""""'•■ "!'•"' inttalmcnls. ihe inaximnm reward of / io.ooo. Ilarrlum »i« a Yorkshire car|icntcr, wlio would have had Utile i hanic «/ er sie tnit nichts andirm hesser zu vtrgkkhen wisse "), because he kr.ew nothing better to liken them to. For more than a century Hovel's map was the best map of the moon. The first telescopic observers soon found : the lunar hemisphere turned earthward is always the same, or nearly the same. The diff- erence there is, is due to libration and its maximum amount is not a forty-ninth of the moon's circum''erence, or more exactly is 7 degrees, 53 minutes of lunar measurement. To that extent only the moon changes the face turned earthward. The rest of her sphere is hidden forever from mortal sight. Hovel was first to explain that libration in longitude is due to the fact, the moon rotates on her axis 'at a uniform rate, while her movement of translation varies in velocity with her varying distance from the earth. Galileo had already found out that there is a similar liliration in latitude, due to the moon's axis of rotation not being exactly perpendicular to the plane of her orbit. In 1651, J. B. Riccioli, a member of the Society of Jesus, com- piled a lunar map noteworthy chiefly from its nomenclature. In lieu of Hovel's names, he designated the craters and places marked on his map after names of eminent mathematicians and astronomers. A French astronomer archly says : " Riccioli shrewdly avoided the During the te ^ "'""= "'oon printed powers from ,J, " ''>' "'^'■'- Predecessor, '" '"'"^- '«='ined. He firL H '"''°"'' "^'=' ^"^ ''«y of hi """"'■^ '" ">= "'>'' Ro.a„ alphabe.: " "'"^'^ "--''. by 'et.et ^n^e S" In 1824, l.ohrnian, of Dresden, proposed to issue in twemy- five sections a lunar map 36 'j inclies to the moon's diameter ; l)Ut, his sight failing, oily fou' sections were printed. As I.ohrman #as a professional surveyor, and was assisted by the astronomer Encke, and used one of the celebrated telescopes made by I'rauenhofer, of Munich, his work had rare merit, and is still referred to. In 1834-6 appeared the map of the moon, by Beer and Mx>dler. It was on a scale of 3 ft. 2 in. to the moons diameter, and was fol- lowed the next year by their great explanatory work--Z>f»- -Uond .■ Oder allgemeine verglekhende Selenography. Their labors carried lunar investigation far beyond the most advanced stages reached by their predecessors. Their book of more than 4°° closely-printed pages, for exhaustive descriptions, and their map for minute details, won them unstinted praise, and still command the highest esteem. Later workers in their field of labor have employed more powerful instruments and made out details they (ailed to record, but their drawings and descriptions are still standards of authority, and are likely to remain such. Their mode of working shows the value of their work. To fix ninety-two chief points on the moon's disk, as bases for further measurements, they made nearly a thousand micrometric measurements from the limb of the tnoon. They also measured one hundred and forty-eight lunar formations with the micrometer. They made one thousand and ninety-five measure- ments of the shadows thrown by eight hundrea and thirty different lunar mountains, minutely noting particulars of illumination at each measurement. From the length of these shadows the height of each mountain was carefully computed, and the resultant heights served as standards for determining the elevation of minor peaks whose shadows were jirojected under like conditions of illumination. They named one hundred and fifty lunar formations not named before, but made no innovations on the accepted nomenclature except that in carrying out Schrcuter's plan of designating unnamed craters by Greek and Roman letters they used Greek letters only for elevations, lower-case Roman letters (or depressions, and Roman capitals for measured points. Their telescope was a Frauenhofer refractor of %i/i in. aperture, having a magnifying power ranging from one hun- dred and forty to three hundred diameters. They worked chiefly with an aperture of 4; 2 in., and did not often use so high a power as 300. As Lohrman had done before them, they followed Schrceter's systen, of describing by luimbers the relative bri-htness of objects they observed. Their scale, since in common use, runs from zero for shadows to 10 degrees for the brightest lights. Beer and Ma;dler's great work enjoys the reputation of being a model sc.entific monograph. Without trace of vanity or egotism the workman in it is lost in his work. One of them, not content with his protracted labor on a difficult portion of the moon's disk, adds • Qu.e potui feci, faciant me/iora polenUs. Involunta.y one b.nvs in respect to these plodding, sincere workers, as tbey say in conclusion ■ "The time and strength our labois have taken, make us aware this "is the chief work of our lives, but our toil will be rewarded if it " meet the expectations of the scientific world." Beer was a Cerman banker, brother of Meyerbeer, the musical composer. Schmidt, of Athens, for many years held a chief place of honor among observers of lunar phenomena. He made more than a thous- and origmal drawings for a lunar map 75 in. in diameter His map was completed more than thirty years ago, though publication was delayed from the question of cost. In .864, the British Association appointed a "Moon Commit- tee," of which Mr. Birt was secretary. They decided to map the lunar surface on a scale of too in. to the moon's disk, and to use for that purpose a telescope magnifying 1000 times. It was decided to use prehmmary sketch maps double the size of the map to be fin.n'ly engraved. Some of the sketch maps were issued, but I am not aware that the finished map has ever been published. Among English writers on lunar subjects, Nasmyth, the cele- brated e. leer who invented the steam hammer, is entitled 10 a high place. His book, " The Moon considered as a planet, a world, and a satellite," was issued in conjunction with Mr. Carpenter and has run through several editions. It is much prized for its chapters concerning the physical condition of the moon, and for its exquisite diawings of lunar craters, mountains and plains. Nasmyth's excep- tional skill in drawing never shone to more advantage than in his illustrations of lunar scenery. In his most interesting biography Nasmyth describes his method of obtaining these illustration. He first made, directly at the • lescope, careful drawings of the part of the moon's disk selected for description. Full notes were taken with the 1 '3 sketch as to illumination and other particulars to be kept in mind. The drawing, with its craters, mountains, rills, with all details of the part of the lunar surface adjacent, were next modelled in clay, and frotn the clay models, after tliey were dried and corrected by furiher tel- escopic observation, plaster casts were taken. These casts were then carefully illuminated to throw shadows similar to those projected by the objects when the drawing was made, and finally they were photo- graphed. l!y such an unexampled expenditure of time and skil , were obtained those contrasts of light and shade, and delicate half tints, which make the Nasmyth lunar drawings so exquisitely beautiful. To the instructive writings on lunar subjects by Webb, Elger and other popular writers, it is needless to refer. Nor need mention be made of the writings and eloquent addresses on these subjects by the late Prof. Proctor. His works speaks best for themselves to all who care for astronomical instruction. The most complete treatise accessible to English readers con- cerning the moon is that published a few years since for Mr^ E. Nelson F. R. A. S Professedly based ot the great work of Beer and Midler, it has original merit, and not only includes his own observations for eight years, but those of Mr. Webb and other obser- vers who aided him in his work, and also contains much interestmg matter from the works of Schneter and of Lohrman. His instru- ments were of the best class, and included a fine 6 in. refractor, and agyi in. With-Browning silvered glass reflector. The lunar map accompanying his book is in twenty-two sections, and is on a scale of two feet to the moon's diameter. Though his chart is more than third smaller than that of Beer and Ma;dler, it is finely engraved, shewing more formations than are given in their map, and more nils than are shewn by Schmidt in his " r,7/eii an dem Mond." Neison groups the lunar surface under the names of plains, craters and mountains. His plains include u ,he large, dark, com- paratively smooth tracts, called by the early selenographers Marm ; the smaller tracts they named />«/«, Laa■ than doubled. ' '° f"^"^"' "J^'^ 'hat number is more dred:s::::;tr;::::.r-:<^ ^'^"':-- -"^ '°" ^"n- he adds eighty.six others, Z^ ^^Z "" ""' "'"■ '''o "^"^ dred and thirteen formati„nr,.tVo ''th:'""";" '" ''' """■ order of its place, and for easy refe^ncc Tu 1 '''"'""' '" "«' g-en. For ever,- formation he ctes lu" Y'"' "'' " "'^ degree 0. brightness, and for c a , ,„, t? '^ '" """"^ """ stons. and for mountains their heil 1 h '"" ''"" ''""- and longitude is given for each formation in'"'""" '" '""" '""""^^ ■n some to seconds. Mi„u,e nar^d ' , '°" "''''" '^ """"'^'s. parts of specal interest, wi 'am " l'" " ^"""''^'^ ^""^-g ^■ion. Tables and formuK. a," „ °!""'" '"" '''' "' <"''"va book may be of service to studel h """" "" ^''''"' """ "'^ work. In proof of the meTo ^hf Cot U '"''""' '" ""''"^^ German so soon as published "'*' translated into -"rr,t:;-™in. .e..,„,_, n.any years ago took excellent tunarn" """'^ °^ ^'^^ York, speculum he himself mad a JmoLr"'"' """« ' ''"'""^ S'as photographs. Prof Rur^ford of NeV";"" '^' '"' '^''"^ '""ar art to still greater degree oSe,L" a^d ' u"'"'' ''"''' "- Pett.ors in all parts of the world '0!,' ""'°"«'' ''^ ^ad com- the latest edition of the Kncy oUdTa T'"''"' ''"'^'' «"""« '" ford the compliment of ca iL hrthe TT'' "''' ^''- ^"'^"■ 'hat had then been taken 'D^unlhlct'"'"'*^ "' ""= '"-" lunar pictures have been taken 7 , ^ '"'^ •"•«■ ''"^ellent observatories in various par of hTZrU ''t "''' ''^''°"°™-' from the Lick and Yerkes L . ' "'°'' f"-""' Paris and highly esteemed. observatories being widely known and The field Of lunar investigation is large, its laborers many, and I '5 are cost.y, taxmR as 'hev d observatories, and the ',ore than a tenth part o. such magn.fy.ng power ,s at present 1 6 able The moon's disk subtends an angle of about half a degree, and mapping the lunar surface into 360 degrees of latitude and longi- tude d lunar degree at the centre of the disk measures nearly i(> miles Little that man has wrought on earth, could his most gigan- tic work be transferred to the moon, would attract much if any notice at the earth's distance, though if man's handiwork would pass un noticed, .0 important lunar formation could now disappear or be materially changed, and elude detection. At the centre of the moon s disk, one second of arc equals 1.1585, more than one and a tenth English miles. What portion of the star sphere a second of arc covers may be realized by calling to mind, a linear foot subtends a second of arc at 39 miles distance, and that the pole-star and its com- panion are 18 seconds of arc apart. In the present stage of re':arch there is divergence of opinion on many questions of lunar physics, though not more than might be expected from independent investigation. Kessel estimated the moon's atmosphere to be a thousandth the density of that of the earth, while Neison considers it to be greater than Bessel's eslimate_ Nasmyth, on the other hand, concludes that the moon is devoid of water, atmosphere and soil, and excepting contraction and expansion of the lunar crust from change of temperature, he thinks the mcon now undergoes but little change. That there is great variation of temperature on the moon's surface from exposure for half a lunation to the sun, anH from radiation of lunar heat into space for a like period admits of no doubt. The six foot speculum of Earl Ross' great telescope was, some years since, used for investigating the probable temperature of the moon. Earl Ross considered his researches tentative, and results approximate only. From his ex- perimems and observations it was concluded that the difference between maximum and minimum temperature at the moon's surface is 200 degrees Centigrade. This difference in temperature between lunar mid-day and midnight was computed from measurement of the mcon's radiant heat. This agrees in part with Sir John Herschel's estimate of the moon's climate. He writes : " The lunar "day is one of unmitigated burning sunshine, fiercer than an " equatorial noon, continued for a time equal to our fortnight, and "th lunar night is a period of the keenest severity of frost, exceed- "ing that of our polar winter, and of the same length as the "lunar day."