[ 3^0 ] 
have got at the rate of 6", 3 upon fidereal time in 24 hours. 
By the fetting of four ftars behind the hill, obferved with the 
telefcope of the equal altitude inftrument, January 29 th , and 
again February 7 th and 8 th (after the manner defcribed by Mr. 
Mafon in his account of the going of Mr. Ellicott’s clock de- 
termined by him and myfelf in this manner, Phil. Tranf. 
Vol. LII. Part II. Page 534.) the clock appeared to get 6", 25 
upon fidereal time in one revolution of the ftars, which agrees 
exa£Uy with the former determination by the fun’s equal alti- 
tudes. In like manner, I always found the going of the clock, 
determined by thefe two different methods, would come out as 
nearly the fame as the equal altitudes of the fun could be de- 
pended upon, that is to fay, to a fecond, even from the obferva- 
tions of two fucceflive days. 
I muft not pafs by this occafion, without taking notice of 
fome remarks, which Mr. Short paffes on my method of ex- 
amining the going of the clock, by obferving ftars fetting be- 
hind a hill, with the telefcope of the equal altitude inftrument ; 
(vide Mr. Short’s account of Mr. Mafon’s paper concerning the 
going of Mr. Ellicott’s clock at St. Helena. Phil. Tranf. 
Vol. LII. Part II. Page 540). Mr. Short reprefents Mr. Mafon, 
as faying in his paper, that I propofed making ufe of the equal 
altitude inftrument to determine the regularity of the motion of 
Mr. Ellicott’s clock, by obferving the vanifhing of the ftars out 
of the field of the telefcope, an expreffion not contained in Mr. 
Mafon’s paper, who is only fpeaking of our obferving ftars 
fetting behind a hill, at the diftance of a quarter of a mile, in 
the fame part of the field of the equal altitude inftrument. Had 
we proceeded in the method fuppofed in the remarks, no doubt 
the obfervations would have been liable to confiderable inac- 
curacy : but as we ufed the telefcope of the equal altitude in- 
ftrument, only to aflift the fight in obferving the ftars fetting 
behind the hill, we were liable to no other error than what might 
arife from the fmall alterations of the inftrument, ariftng from 
the changes of heat and cold, moifture and drinefs, feen from 
the diftance of the top of the hill, which will eafily be allowed 
to be quite infenfible. And, indeed, how otherwise could the 
obfervations, contained in Mr. Mafon’s paper, agree fo well to- 
gether as they do ? A circumftance alone fufficient to create a 
iufpicion of the obje&ion being ill grounded. The reafon of 
Mr. Mafon and myfelf always obferving the ftars to vanifti be- 
hind the hill, in the fame part of the field of the telefcope (that 
is, 
