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ASTRONOMICAL PAPERS. 



1 63' 



circiu 



mftances is requifite, tliat neillier the former tranfit 



of 1 76 1, nor, it is feared, this of 1769, will enable aftrp- 

 nomers to do iuftice to the Doaor's noble problem in all its 



parts 



rft 



J 



For it ivS neceffary 



tclefcopes, time-pieces well adjufted, and the latitude and 

 loivntude of their places of obfervation determined with 

 the moft fcrupulous exadnefs. 



Secondly, That the abfolute difference of time between 

 the contads, at the different places to be compared with 

 each other, be fo great, as to render the unavoidable fmall 

 defcds of inftruments and obfervation infignificant. 



Thirdly >, That all the obfervers be favoured with a clear" 

 flcy, and the Sun of a fufficient altitude, not lefs than 8^- 

 or i o"* above the horizon. 



Granting therefore, wliat 1 believe will not be denied, 

 that all the circumftances mentioned under the firft head,, 

 concurred in favor of the American as well as European 

 obfervations made ufe of in the following dedudion of the 

 Sun's parallax; yet the abfolute difference of time, being 

 on a mean, but about 3/. 4'', was fcarce one fourth part 

 of the greareft abfolute difference that might be obtained, 

 from obfervations made at two places fituated in the moft 

 favourable manner, with refpcft to each other. 



But though this circumftance did not concur in favor 

 of the European and American obfervers, yet, if the Sun. 



had been fufficicntly high to the former, and as refplendent 

 and well defined as he was to us, notwithftandingthe fmall 

 difference of abfolute time between our obfervations, his 

 parallax.might have been deduced from them, perhaps to 

 as <^reat exadnefs as ever it canbeexpeded from a tranfit 

 of Venus. For any two obfervers with us, having eyes 

 and inftruments equally good, and taking the fame method, 

 of judging concerning any pha^nomenon^ could fcarcely 

 have differed more than s\ or &'\ and where feveral ob- 

 fervers were at one place, it is probable the mean of all, 

 might have brouglit the time within the limits propofed 

 by Dr. Hallcy, tliat is within 2" of the truth. But 



