VARIABLE STARS. 271 



neceHary to give velocity to heavy bodies, where he fuppofes^^^^^^fpof 



rt- ,11 111 J 1- i mechanic pawerj 



a man puming an iron ball on an extended plane, ana this not oreffedl, 



to try his mufcular force, or to fee what he can do without 



tiring, but merely in elucidatio'n of the do6lrine he fets out 



with. 



I have not time at prefent to purfue the fubjecl to the 



extent I widi, and to enter on the gfound of the miflake of 



this great man : nor let it be imagined for a moment that I 



have availed ttiyfelf of his everlafting abfence, to call in 



queftion what he' has advanced in refutation of a fuppofed 



error. It would have remained as it was unto a diftant period, 



had it not been, that' I fee Mr. Gregory advancing the (ime 



opinion, which no doiibt he will defend or defert. 



I am. Dear Sir, 



Your obedient Servant, 



J. C. HORNBLOWER. 



If Mr. Gregory (hould read this, I (hall be glad if he will 

 fet me right as to the identity of animal exertion and mechanic 

 pouer. 



VII. 



jin Invejiigalion of all the Changes of the variable Star in Sobiejld'a 

 Shield f from five Years Ohfervations ; exhibiting it^ propor* 

 tional illuminated Parts, and its Irregularities of Rotation ; 

 with Conjectures refpedling unenlightened heavenly Bodies. By 

 Edward Pigott, Efti^ Abridged from the Philofophical 

 TrajfaSiions for 1 805 . 



T, 



HE author begins his memoir with an inveftigation of the The variable ' 



periods of change in the variable ftar in Sobie(ki*s (hield, of ^^^'P^°^'^^^'^ 



I • I . . , r r- o T/ ,.,,.. Aield, revolves 



which the right alcenhon was 279*' 9f, and its declination on its axis in 



foiilh 5° 56', for end of June 1796. Its rotation on its axis 6if days. 



in 1796 was eftimated at 62| days, from a mean of fix obfer- 



vations of its greatetl and leafl brightnefs. In the prefent 



paper he gives about 26 fimilar determinations, moft of them 



the refults of very accurate ohfervations made i^, the year 



1796, 1797, 171*3, 1799, and 1801. From all thefe refults 



it 



