"^^^z^^A^vi^^^in:^ ^ — 



94 



MATHEMATICAL and 



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1 ' 



place of obfervatlon, to a critical exadnefs; and this wa 

 proved by accurate menfuration. Thcfe were certainly very 

 diverting experiments to an inquifitive mind! The gen- 

 tlemen who alfifted us through thefe experiments, and like- 

 wife la the reft: of our \york, were the Hon. Stephen 

 Hopkins, Efq. Mr. Mofcs I3rown, Dr. Jabcz Bov/ea, Jo- 

 feph Naili, Efq. and Capt, John Burrough. 



" The regulation of our clocks, being of the utmoil 

 confequence in this affair, was what next commanded our 

 attention. In this part of the work we endeavoured to 

 arrive at as great a degree of certainty as the nature of the 

 cafe would admit. — Several workmen were employed in 

 laying a platform of feafoned pine plank, as fmooth and le- 

 vel as art could make it: This was fecured from rain, 

 or other moifture, that it might not warp when expofcd to 

 the Sun. We examined this platform three times a day 

 (when the weather would admit of it) with a very long 

 level. On the fouth fide of the platform, and exadly per- 

 pendicular to it, we ercded a ftile ten feet high; this was 

 likewife examined three times a day. We next perfor- 

 ated a piece of board, into which was fixed the glafs of a 

 fcioptric ball, fo that the center of the glafs was exadly in 

 the center of the perforation; this board was fo cut, and 

 let in at the top of the ftile, that it turned upon an axis 

 in fuch a manner, that the center of the glafs did not alter 

 its pofition. The Sun's rays were tranfmitted through 



the lens upon the platform, where they were formed into 

 a bright fpot, and very diftindly defined. From the cen- 

 ter of the lens was let fall a pcrpendicidar upon the plat- 

 form; from that point, as a center, was drawn a great 

 number of concentric circles, for taking correfpondent 

 Ihades, in order to trace a meridian line; and, 

 wiflics would have it, the weather proved favorable for 

 this work. When the line was drawn^, I found from cal- 

 culation, it declined 3" in time, eaft of the true meridian; 



this 



X 

 5 



--, 



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as 



our 



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* The magnetic needle, being placed on his exad meridian line, was found to differ from 



i t 6^' ^ wtflward. 



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