Mr. Sme atom's Obfcrvation of Mercury 
* 1 3 
Explanation of the lefs obvious parts of the Tables of the Obferva~ 
tion of Mercury near his Elongation , Sept. 1786. 
The third column of Tab. I contains the times of obferva- 
tion as they were taken down from the half-fecond journeyman 
clock, in minutes, quarters, and beats , according to the following 
method ; which was, by taking up the beat when the fecond 
hand came to 15, 30, 45, or 60, and then counting 30 beats re- 
peatedly till the arrival of the object at the middle of the wire it 
was approaching ; after its arrival, the beats (or interval be- 
tween two beats) being retained in memory, and the eye cad 
upon the dial-plate, it was eafily feen whether it was fo many 
beats more than the quarter, the half, three-quarters, or the 
whole minute, and was fet down accordingly. Thofe reduced 
to minutes, feconds, and tenths of feconds, by allowing .2 or .3 
for the quarter fecond, .5. the half, and .7 or .8 for the three- 
quarters of a fecond, are contained in the fourth column. The 
reduction of the fourth column to the f fth was by means of the 
auxiliary Tab. II.; and Mercury being then nearly da tion ary 
refpeffing the fun, the fun’s run was ufed for the planet in- 
dead of that of a dar. The mean of each fet of obfervations 
of the fifth column is carried into the fixth. 
The feventh column contains the parts of the micrometer 
as they were read off; to render which intelligible, it is to be 
noted, that the declination wire A travels from the upper fide 
of the field of view of the telefcope towards the center, and 
fomewhat beyond it : and upon it are taken all the objects that 
pafs the field of view on the upper fide, anfwerable (by inver- 
fion of the objecd) to the font hern half of the field ; and in 
like manner thofe that pafs the field of view on the lower 
2 half 
