XLII. Account of the transit of Mercury, observed at Norriton, in Pennsylvania, Nov. 9. 1769 agreeable to an appointment of the American Philosophical Society, held at Philadelphia, for promoting useful knowledge [ 5°4 ] X L II. A ccou n t o f the T ranfit o f Mercury, obfervedat Norriton, in Penniylvania, Nov. 9. 1769 agreeable to an A p p o in t­ m ent o f the American PhilofophicalSocietyy held ^/ Philadelphia, /2?r promoting ufeful Knowledge. ^ William Smith, Z>. D . Provoflo f the College o f Philadelphia 5 John Lukens E fq \ S urveyor G en era l o f Pennfylvania; David Rittenhoufe, M . A . a n d MnOwen Biddle. Communicated by Benjamin Franklin, L L . D . a n d Prefident o f the P h U fo p h ic a l Society a t Philadelphia. Read Dec. i | , j k S Iran fi ts of M e reury are more fne* / \ quent than thofe of Venus, we need not be fo particular in this account, as we were in that of Venus. W e had the fame telefcopes now as before, viz 1. T h e college reflector, with Dollond’s microme­ te r; ufed by myfelf, with a magnifying power o f 200, to obferve the contaBs, t, A refractor of 42 feet, magnifying 140 times, ufed by M r. Lukens* - ; * 3. M r. 6 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 5°5 ] 3. M r. Rittenhoufe’s refractor, with about the fame power, ufed by himfelf. M r. Biddle had no telefcope; but was very fervice- able in the other parts of the obfervation. * Although there were many flying clouds, w hich frequently obfcured the Sun in the forenoon of the d a y ; yet from about one o’clock till half an hour paft three, the Sun fhone perfectly clear, and undifturbed by clouds $ which gave us an opportunity, as favora­ ble as we could with, for obferving the contacts, and making fome micrometer meafures. T h e firft external contadt was obferved to the fame inftant by all the three obfervers, who had no com­ munication with each other, the two refradtors being out of doors, and the refle&or within the obfervatory 5 and the contadts noted (as at the tranfit o f Venus) by fignals given to perfons fet at the windows of the o h - fervatory, to count the clock. T h e contadfs were as follows: 1769, N ov. 9, apparent time, Jt 9t t f A t 2 35 vjfirft external c o n ta d t,b y all the three obfervers. 2 3 d 35 firft internal contadl, by D r. Smith and Mr. Rittenhoufe. 2 36 33 firft internal contadt, by M r. Lukens* I n , 2 0 tfer 5 0 0 th3 ' ©:’s diarru per microm. 3 13 7 M ercury’s diam. taken backwards an d ' forwards feveral times, and the fum > halved, gave only 32 2 0 ,2 4 0 8 ,2 2 V o u L X . T i 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 £ 5 ° 6 ] Nov. 9, 1769. Micrometer meafures of Reduced to M$. apparent time. leait diftance of the nearcil nutesand Seconds * limbs of O and . of 0 ’s Diameter.J, t In. 20*11* 500th* / / / 3 1 4 4 0 5 14 d o u b t f u l 2 2 6 , 2 3 ‘ 9 0 6 1 2 2 5 0 , 5 3 19 7 0 8 1 3 3 ! >8 4 3 3 1 M 0 1 0 0 4 2 3>78 From 3 1 minutes part: three, the fun was con-' dantly oblcuredin a cloud, that defcended with him , till at 32' part 4 he broke out into a fhort glimpfe o f three m in u tes; during w hich the diameter o f $ was again meafured, and came out as before. One mi­ crometer meafure more was alfo now attempted o f the neared didance o f the limbs, but the o got under a cloud before it was completed, to our great regret, as we wifhed to have at lead one more meafure at an hour’s didance from the red. More might have been taken during the iird h alf hour, after th re e ; but thofe that were taken are diffidently near each other, and any between them would have been ufe- lefs for a proje&ion, as thofe we have may be de­ pended on. T h e following obfervations o f another kind were all that M r. Rittenhoufe could obtain, Apparent tim e. h / / / 3 3 30 O ’s lower limb at horizontal wire. .3 3 42 o ’s preceding limb at vertical wire. 3 5 58 $ *scenter at vertical wire. 3 6 3 1 o ’s fubfequent lim b at vertical wire. 3 6 3 2 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 h r n 3 6 32 5 ’s center at horizontal wire. 3 7 18 o ’s upper limb at horizontal wire- 4 3 0 34 o ’s lower limb at horizontal wire- 4 3 1 4 © ’s preceding limb at vertical, 4 3 2 39 $ ’s center at vertical, , 4 33 41 o s upper limb at horizontal. * T h e two remaining obfervations o f this fett could not be got, the fun being again obfcured by a cloud* and appearing no more that day. T h ey had fome- thing more of the fun at Philadelphia, and got fome micrometer meafures after four o’clock. By the con­ tacts of mercury at Philadelphia and Norriton, we get the latter 5 5 " of time weft of the ftate-houfe. obfervatory; the fame we made by the eclipfes o f Jupiter’s fatellites. [ 5°7 ] Philadelphia, W . S m i t h * Dec. ig, 1769, T t t 2 i XUS. A 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