a floating collimator. 
i6l 
loth Set. 
Divisions 
of 
Microm. 
Difference. 
Error in See*, 
affecting the 
Horiz. point. 
Dec. 1 1 
Out and replaced, S first 
Ditto - ditto 
Ditto - - ditto 
Ditto - - ditto 
Ditto - ditto 
Ditto - - ditto 
95>7 
96.7 
99.5 
98,2 
97.0 
97.7 
+ I.o 
+ 2,8 
— 1.3 
— 1,2 
+ 0,7 
+ 0,30 
+ 0,84 
— 0,39 
— 0,36 
+ 0,21 
The float pressed upon the mercury as before, and the 
mean of the readings of both angles of the cross wires 
taken. 
I ith Set. 
Out and replaced, S first 
Ditto' - - ditto - - - 
Ditto - - ditto - 
Ditto - - ditto - 
Ditto - - ditto - 
Ditto - - ditto - - - 
97.4 
98,1 
100,5 
93.8 
95.0 
94.6 
+ 0,7 
+ 2,4 
— 6,7 
+ 1.2 
— 0,4 
// 
+ 0,21 
+ 0,72 
— 2,01 
+ 0,36 
— 0,1 2 
In the preceding experiments it may be seen that by far 
the greater number of the results are negative, or that the 
readings of the micrometer for the most part gradually de- 
crease. I felt much at a loss to account for this, and at first 
supposed it to have been occasioned by the vicinity of the 
lamp to the Y supporting the cross wires ; but I found on 
trial that this was not the fact ; indeed in that case the effect 
would have been the reverse of what was observed. I can 
in no other way account for it than by supposing that as the 
weather was very damp and cold, my approach to the stand 
which supported the micrometer, caused the legs which were 
MDCCCXXV. Y 
