S3 8 Mr. Barlow’s observations and experiments on the 
will be sufficient to observe, that I paid the utmost attention 
to this essential condition, and that I believe my want of 
success did not arise from any defect in this part of the pro- 
cess, but from the extreme delicacy of this instrument, and 
the consequent difficulty in adjusting it when under the in- 
fluence of the neutralizing magnets. I tried its action for 
three weeks in the house, but the jarring of doors and other 
circumstances prevented me from drawing any conclusions ; 
I then removed it to the garden, to a spot well protected by 
trees and shrubs, and fixed the entire apparatus to my garden 
wall, which is exactly in the magnetic meridian ; and farther 
sheltered the whole in the best way I could from the effects 
of the wind and weather. Indeed the only inconvenience 
was that I could not leave the needle out in the night, and 
could therefore only notice what took place in the day time, 
and this, as I have said above, was not so uniform as I could 
have desired. 
In general a motion commenced soon after the instrument 
was adjusted in the morning ; but it was not of that gradual 
and progressive kind which indicated an uniformly increasing 
or decreasing power, as in the other instrument ; it passed, 
for instance, suddenly from one half or quarter degree, to 
another more or less, and which sometimes in the course of 
the day would give a difference in the dip to the amount of 
a degree and a half, or even more, but I seldom saw in it a 
tendency to return ; although when I vibrated it towards 
night, it commonly took up its morning position. I made 
these observations with the needle in various directions, viz. 
with the face of the instrument to the east, west, north, 
south, &c. but in every case I obtained the same sort of daily 
motion. The question, therefore, respecting the law of va- 
