[ 2 3 
I had fettled the going of an excellent clock, re- 
gulated according to mean time, by correfponding al- 
titudes of the fun taken the 14th, 15th, 1 6th, and 
17th of Auguft, and by the meridian tranlits taken 
by an inilrument, of five feet focus, on the 12, 13, 
14, 15, and 17. fo that no doubt remained about the 
motion of this clock, which was extremely regular. 
To make the obfervation, I made ufe of a very 
good Gregorian refledor of 12 inches focus, the great 
mirror being three inches diameter, which magni- 
fied that of the objeds about 40 times. This in- 
ftrument was mounted upon a paralladic machine, 
extremely commodious, and having very eafy mo- 
tions. The telelcope was furnifhed with a micro- 
meter with filken threads, inclinable on all iides, fo 
that it was eafy to place it according to the motion 
of the fun, and to incline it in fuch a manner, as to 
meafure the diftances of the horns and the magnitude 
of the Eclipfe. One might likewife have adapted to 
this inftrument an objed glafs micrometer of 24 feet 
focal length ; but I rather chofe to make ufe of the 
iil ken threaded micrometer, which was more con- 
venient, and eafier to be managed. Here follow the 
obfervations. 
J 755 
