LXIX. Observations of the transit of Venus over the Sun, June 3, 1769; made by Mr. Owen Biddle and Mr. Joel Bayley, at Lewestown, in Pennsylvania. Communicated by Benjamin Franklin, LL.D. F. R. S f 4 *4 ] LXIX. Obfervations of fie of Venus over the Sun*, June 3, J 769 ; made by Mr. Owen Biddle and Mr. Joel Bayley, at Leweftown, -in Pennfylvania. Communicated by Benjamin Franklin, L L . D . F . R I S . Read Dec. 21, N the 26th o f M ay, 1769, Joel Bayly and myfelf arrived at Lewef­ town (on Cape H inlopen at th e m outh o f D elaw are Bay), being ordered there, by the American Philofo- phicai Society, held at Philadelphia, for prom oting ufeful knowledge, to take an obfervation o f the en- 1 filing tranfit o f Venus over the Sun’s d ifc ; and im ­ mediately fet about fixing our tim e-piece, in a houfe (w hich we h ired ) on the fouth ftreet of the tow n, where w e were m od likely to be free from interrup­ tion, and had an open view of the Sun and ftars for our obfervations. W e let a ftrong oak poft in the ground, to w hich w e fcrewed our clock cafe, refting the Dale o f it on the ground, the face of it fronting a door w hich opens to th e fouthward, fo as to be con­ venient for us to hear the beat of the clock, where we intended to fix our telefcopes and inftrum ent for taking equal altitudes. W 6then let a port in the g.’ouad for the equal altitude inftrum ent, which was n o t D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 C 4 1 5 ] not fo good as I wifhedj b u t m uch better than a H a d - ley’s quadrant, as we found by experience, and the beft we could procure in time for our purpofe. It was a theodolite, w ith telefcopic fights, in w hich there were crofs hairs j it had a fpirit level to adjuft the plain o f the inftrum ent horizontally; and alfo one applied to the te l^ q g e p a ra U e l with its axis, and at right angles to th e other fpirit level. By means o f thefe tw o levels and adjufting fcrews, we found we could adjuft it very nearly, the inftrum ent being a very good one o f the kind. W ith this we let our clock, by taking equal altitudes o f the Sun, which we corre&ed by the tables publifhed in a pam phlet, in- titled, Inftrudtions relative to the enfuing Tranfit. o f Venus, &c. by the Rev. M r. Nevil M alkelyne. T h e 27th, we got fome good correfponding altitudes o f the Sun, by which we fet ou r c l o c k a n d • took, equal altitudes o f fome o f the fixed ftars, to prove the rate o f our c lo c k A fter this it continued cloudy, w ith rain at times, and a high wind at north-eaft, till the 31 ft, when the clouds broke a little. D uring this time, we employed ourfelves in meafuring the diftance of our place of obfervation from the ftone fixed at the beginning, or eaft end, o f the eart and. weft line, which is the boundary between the three, lower counties and M aryland, and is fituate on F en ­ wick’s Ifla n d ; the latitude and longitude o f this place being accurately determined by Meflieurs Dixon, and Mafon. T h e meridional difference o f the latitude of the place of our obfervation, north from Fenw ick’s Iftand, at the beginning of the eaft and weft line, as before defcribed, being the eafternmoft end o f the fouthern. boundary D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 | 416 I ̂ | ’boundary between the lower counties and M a ry la n d the meridional, difference o f longitude o f the place o f our obfervation, w eft from! th e : point aforefaid, in Fenw ick’s Ifland, 5 ' 45 7 o f a, degree. Thefe data, with the latitude and longitude* o f Station Point, w ill determ ine exactly the place, o f obfervation. n b vltnj June 2, the weather being clear,, had good, coc- relponding obfervations o f the -Sum y; Ju n e 3., the h a d good.obfervations to ftt our clock*, A bout i z ^ c lo c f c begati to d ire d our glaffes, to. >the Sun, keeping if continually in the field frorn then to the tim e,the ob­ fervation was paft. VVe. a g ^ d j p w atdh^our te- lefcope one minute in tu rn , till about (even o r eig h t minutes before the contact w a s e x ^ f t e d , left, by, too fteady an attention to th e glaffes, our fight, thou Id be im paired, '?lh& co n tad clearly. I had left i m y telgfcope the m inute preceding: the contact, intending to apply m yfelf fteadily to it, from the next minutej until the obferva*-. tion was paft -9and w hen the-48th ftcondl wascalled* I applied m yfelf to the glafs, and by the time three ftconds were elapfed, J pgceived, op th a t p a r t o f the Sun's lim b where I expeded th e contad* a fmaifitn-* prefijon, w h ich proved to be th,e-lim bo f ..Venus ii* co n fa ^ w ith th e Sun. A ll th e lim b ojf the Sun* w hich appeared at th at tirne i n t h e f t d a of the te - lefcope, had a fmall undulatory motion, which, I ap p r^ien d , was pwing to, m p fe vapours, which arofe at iea. ,fA t| V enues 4firft a p t^ a ra p re . to tn% it. was only likeftone o f thofe waves pm t h e ^ o f b ^ d f r o f the Sun, incieaftd in D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 t *4 *7. } fo fmall a proportion, that I remained doubtful fo r feverai feconds, w hether i t was any thing e lie ; " thus it continued) m aking a deeper impreflion, w ith that tremulous motion, for about ten feconds, when th e trem or where Venus was in contact ceafed, and the indenture was truly circular, w ith an even term i­ nation. M y abfence from the telefcope, ju f t before the contact occurred, deprived m e o f an opportunity of judging w hether there was any appearance o f an at- mofphere preceding the weftern limb o f Venus in co n tact; but w hen Venus had entered nearly one h alf o f its diameter into the Sun’s difc, m y compa­ nion and myfelf faw a lum inous crefceht, w hich enlightened that part of Venus’s circumference Which was off* the Sun, fo that the whole, o f her d r c u m - ference was vifible, but did not continue fo until the internal contact $ and at the tim e o f the firft internal contact, the eaftern or external limb o f Venus feerned to be united to the Sun’s lim b by a black protu­ berance or ligament, w hich was not broke by the entrance o f the thread of light, till fo u r feconds after that the regular circumference o f Venus feemed to coincide w ith the Sun’s* T h e telefcope I made ufe o f for viewing the tran* fit, was a reflecting one, belonging to the Philadel­ phia L ibrary Com pany, the fpeculums o f w hich are z \ feet apart, and the lenfes in the eye tube four inches apart j it was the leaft magnifying pow er that I ufed, as I found th e tremulous motion too much magnified by the other power. T h e fmall one wa^ in good order, and defined the Sun’s limb, and fpots on its difc, very clearly. I had applied a polar axis V o l , L IX . H h h to D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 f [ 4>8 } to it> and made fome rack-w ork, by which I could keep the fame part o f th e Sun?sdimb in the field w ith eafe y my companion was not fo well provided w ith a telefcope, the-one h e u fe d b e in g o f D ollond’s refracting glafifes o f 4 I feet. T h is we fixed, with a ball and locket, to a poll:, by w hich it was eafily di­ rected to the Sun. T h u s furniihed, we found th e contacts to take place as follows, reduced to m ean time* h / / / O w en Biddle*s E xternal contaCt at Internal one at Joel Bayley*s E x tern al c o n ta d was" loll by an accident, b u t f^en by h im , after it had taken place, at Internal ditto 2 11 53 2 29 53 >2 12 15 2 2 9 53 I t m uft be noted, the internal eoritad, given by O w en Biddle, is at four feconds before the thread e f light had broken the dark ligament or protu­ berance, by w hich Venus s limb was united* to the Kmb o f the Sun, that being the tihie he eftimated the IWo limbs to be in contad. T h e internal contads, we think, m ay be relied on j the external happening fooner than ex p ed ed , occa- fioned’ a doubt at its appearance, w hich made th e e X r a d fecond o f its appearance a little uncertain. Philadelphia,, June g, 1769. Signed,; ©wen Biddle. Copy, taken in hafte, b u t the times examined bv Owen, Biddle. T h e D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 C 419 ] T h e times o f the conta&s o f Venus w ith the limb o f the Sun, as feen by O w e n Biddle and Joel Bayley o n Gape H inlopen ; w ith the true difference o f latitude < and departure of the place o f their obfervation^ from / the M iddle Point be­ tween F enw ick’s 11fland arid Chefopeak Bay, are as follows, viz. ; i h r E xternal contact at 2 u 53) m e a n tim e Internal c o n ta a a t 2 29 53 J 0T00 T h e difference o f latitude o f the" place o f obfervation, north o f i Middle Point. T h e meridian diftance o f th e ! place o f obfcrvationf s eaft o f > M iddle P o in ts ; 4 v;1, 1 21 ,9 3 m iles 30,6 3 5 6 miles * T h e latitude and longitude o f M iddle Point were taken by Meffieurs Dixon and M afon, and, as w e fuppofe, communicated to the Royal Society, b u t we are not yet acquainted w ith it. N . B. As we are n o t acquainted with the exadfc meafure o f a degree o f latitude, agreeable to th e above gentlem en’s m eafurement, we have fent the difference o f latitude and longitude in miles and decimal parts, as it may be reduced to greater tfcf- tainty thereby. H h h 2 Remarks D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 I m l a rirv/i n wf 4 * 4a jipri ̂fxi [J io ' j oi 15'niiwl inioc: A c R R O V A L . ?yl -^ V 2 ,CL J H V J 4J o V j$Blci£lT .lollff^l S!3.l] F rom the data given abftve, and the length o f a degree of latitude, .foupd 4* IVJeffieurs. M afon and D ixon, in A efe part^ = 6 8 ,^ 9 6 Engliffi miles, th e difference o f latitude q f.L ew efto w n and the M iddle Point above mentiqpe^f: ̂ h i c l ) | da the fame w ith the point A ; fee Meffieurs M afon’s and D ixon’s meal'ure o f a degree, Philof. T ra n fa d . vol. L V I I I . p .2 7 6 ) is 1 9 '5 3 " ; but the latitude o f th e point A was found,. by M effieurs M afon and D ixon 38° 2 7 ' 3 4 " ; therefore that .p f Lew eftow n Is 38° 4 7 ' 2 7 " n o r th ; and th e difference o f its meridian, and th at of the point A , or their difference o f longitude> is 3 4 ' d ,\W° f tim e, Lew eftow n being to th e eaft.’ ‘ B ut if the difference o f longitude o f L ew ef- tQwn eaft o f the Stones on F enw ick’s Ifle be fup- pofed truly given, in th e former account, j* 4 5 " o f ' a degree, then the difference o f longitude o f Lew ef­ tow n an d the point A will come out about o f a degree, or 4 " o f tim e lefs 5 for M r. Dixon acquaints m e, that the diftance o f the Stone on F en wick’s Ifle, caft o f the point A, is 3,5 Englifh miles w a n tin g 100 yards. N o w this is equal to 3 0 ' 2 6 " o f a great circle = 3 8 ' 5 1 " o f longitude 5 from w hich fobtradting 5 ' 4 5 " , there rem ain 33'* 6 " for differ­ ence o f longitude o f Lew eftow n and Point A = 2 ' I 2 /a| o f tim e, or 3 " ! lefs than found b efo re; and this latter I take to be neareft the tru th . I f this be fb, Lew eftow n is very nearly under thq fame meridian w ith the fouthernm oft part o f th e city o f Philadelphia,, or m o re accurately 1 3 " o f longitude, anfwering; D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1 [ 4 2 1 ] anfwering to i / ' o f time, eaft of it. F p r, t y Mpftieurs Mafon’s and Dixon V m eafure o f a degree, the point N (fee Philof. Tranfadt, V ol. L V l i l . p. 2 ? 6 i is 2'. 1 c > f longitude weft of the point A j and N» by m eafarement, is 31 E nglifh miles due weft o f the fouthernmoft part o f the city q f Philadelphia^ an­ fwering r2 / / -of 'lo h g itu d e| from w h !lh |iu l> tra&ing 2 ■ 19 A there'f^nriaih an fw erih g to 2a o f 1tim e f ‘for the1 difference o f longitude of the foutfaernmoft part o f Philadelphia, baft o f the point A. h But Lew eftcwn is found above to be 3 3 ' 6"o f 1'ongittrdb ±± ^ f j f y eaft 6 f the'point A, and confequently of Ibngitqdbf o f aboqt \ tr of time eaft of th e W th ern m o ft part of the city o f Philadelphia;. u 11 ̂ N 13.3" ;; Nevil Mafkelyne, ns Mtwoi 1 i S S l t i s h r 'iiw aftew sJ io3t.irjiigac>J 10 ihii'oi hi"ill I1h! tow ocnrt l o f f i '9 is' II3'1 fi 90 ed Ot 1 13llBI if i l l ID 113 "iSif'M'i 5 5 V |tf III 1"31-s VlliB' 21 i.I W C.i'J 1,3Will,.k f0 i 9 h ■ 3 t f » ill 3|fs ffomoisdfub) sell iitiw 4 f o . - m t f i s i i t i j t K j i 9 i o c o 3 0 : cE i n q * 3 4 s n n 9 L X . Ob'fcr- D ow nl oa de d fr om h tt ps :/ /r oy al so ci et yp ub li sh in g. or g/ o n 05 A pr il 2 02 1