THERMOMETRICAL OBSERVATIONS. 2J5 



large one above mentioned extends to 5 degrees north, 

 and fouth of the zenith, and the fmall one to between 

 8 and 9 degrees. Stars when fo near the zenith are in- 

 fenfibly affedled by the different refradlive poweYs of the 

 atmofphere arifing fr6m,its different degrees of denfity, 

 add to this that the error of the vifual axis is completely 

 corredled by taking the zenith diftances of the flars with 

 the plane, or face of the inftrument both eaft and wefl. 



3dly. A large acrcmatic telefcope made by Mr, Del- 

 land of London, which exclufive of a terreflrial eye piece 

 which magnifies about 60 times has three other eye pieces 

 for celeftial purpofes, the magnifying powers are 120, 

 coo, and 300, the firft I generally ufed. 1 his inffru- 

 ment for producing a well defined clear image is exceed- 

 ed but by few refle£lors. 



4thly. A tranfit and equal altitude inftrument, which 

 I conftrufted and executed in the year 1709, and ufed 

 in running the weftern boundary of the ftate of New 

 York, and afterwards in runnino; the boundaries of the 

 diftridl of Columbia, and the principal avenues in the 

 city of Waftiington. It is mentioned in the 4th Vol. of 

 the Tranfadlions of the American Fhilofophical Society, 

 No. 6. page 49. 



5thly. Two acromatic telefcopes for taking fignals 

 with Aiding tubes, one of them drew out to upwards of 

 4 feet, and the other to about 15 inches, — the latter for 

 its length is remarkably good, it fhews the fatellites of 

 Jupiter veiy diftindly, 



6thly. A regulator which I executed in the year 1784. 



jthly. An inftrument of 8 inches radius for taking 

 horizontal angles, made by the late Mr. George Adams 

 of London, and fimilar to the one defcribed by M. de 

 Maupertuis in the work already mentioned. 



Sthly. Three brafs fextants ; one of them executed by 

 Mr. Ramfden in a fuperior ftyle. It is 7 inches radius, 

 and by the vernier divides to 20 feconds,, v>?hich may be 



Vol. V. E e , again 



