112 



MATHEMAT I C A L and 



/ 



the true difference of our meridians^ which happens to agree 

 to afecond with what you deduced from a comparifoa of 

 all the obfervations with the almanac alone. 



*' If any further obfervations of the eclipfes of Jupiter's 

 fatellites ftall be made the enfuing feafon, I fliall be obli- 

 ged to you for a communication of them ; which will ferve 

 further to confirm the difference of our meridians. 



" The many curious optical pha^nomena noted in your 

 account [of the Noniton obfervations] cannot but be very 

 acceptable to pbilofophical readers. The Sun was too 

 low here to give me an opportunity to oblcrve the firft im- 

 preffion of Venus (perhaps I ought to fay of her atmofphere) 

 in the fame manner you law it. Mr. Hirft's account of 

 his obfervation of the former tranfit 1 761, at Madras, feems 

 to have a great refemblance to yours. But I have feen no 

 fimilar ^ account with refpeCt to the prefent tranfit. Per- 

 haps none of the obfervers had the Sun fo bright and clear 



as you had. 



'« Your meafures of the neareftdiftances of the limbs of 



the Sun and Venus determine very well the neareft ap- 

 proach of Venus to the Sun's center, which was a very 

 important obfervation, and could not be made here. If 

 the appulfes of the limbs of the Sun, and Venus's center, 

 to the hairs of the equal altitude inftrument £hould f arrive 

 in time, I will take care that they be inferted in the place 



left for them. 



" I fee Mr. llittenhoiifc-i in making his projedion, af- 

 fumed 8 ",65 for the Sun's horizontal parallax at the mean 

 diflance; but, by the obfervations of the tranfit in 1761, 

 Mr. Short % and myfclf both found that to be the parallax 



on 



* All the oI)fcrvc];s in this provJiice noted much the fame phitDonicnu asthofc referred to in 



this letter. 



f They were not inferted in our own printed account, for the rcafons}?;iven in p. 33. 



\ Mr. Ritttnhoufc affitmed tiie parallax 8'',65 from Mr. Short's piipcr in Phil. Tranh 

 vol. 52, part 2d. page 621, where the ])arallux of the tiun on t.]ie tranht day, i;6i,is certainly 

 made by Mr. Short V ^S^ and the mean horizontal parallax 8", 65 as talren m our projct51:ion. 

 Mr. Short's words are very clear. , After going through his lahonous and accurate cukulations, 

 from the different obfervations of the tranfit 1761, he concludes asfollows-- — ^' T\xc^ parallax 

 of the Sun being thus found, by the obfervations of the interna! contat^t at the.egrefs = 8'^5^? 

 m the day of the tranfit^ the MEAN iiOKlzoNTAL 1'akai.i.ax oj' the Sun is $"i(}S" 'Wc prefumc 

 then there mufl he fonre fubjequent }Ki])cr of Mr. S/jorl's, and the ajironomcr royal ^ (which wehayc 

 not yetfeen) ibat makes the puraUax of the oun 8", 65 on the day of the tranfit l 761. However 

 the fmall diffcrencs of Icfs than two-tenths of a fecoad will not materially a/fcd the projei5iion 



