daily variation of the horizontal and dipping needles , &c. 339 
riation of this instrument, still remains to be submitted to 
fixed principles, although there can be no longer any doubt 
that it is subject to a daily change. 
On a curious anomaly observed between the daily variations in- 
doors and in the open air. 
I have already mentioned that I was, at the commence- 
ment of my experiments, a good deal embarrassed and de- 
layed by certain anomalies which I noticed between the daily 
changes of the needle made in the house and in the garden. 
These may be stated shortly as follows. That in certain 
positions of the needle towards the east and west, the daily 
motion, although it proceeded with the same determinate 
uniformity in both cases, yet it took place in different direc- 
tions ; passing in the one instance from the east, or west, 
towards the south, and in the other towards the north, at 
the same corresponding hours of the day, the motion in both 
instances being equally distinct, regular, and progressive. 
After carefully examining every circumstance that might 
be supposed to be the cause of this singular change, I could 
only imagine three, that seemed in any way likely to account 
for it. 
1st. Were the two magnets and the compass needle in the 
two cases in precisely the same relative situation ? and if not 
might not the cause lie in this discrepancy ? 
2nd. The window of the room was to the northward ; 
was it possible that the light, arriving at the needle in this 
direction, was the cause of the change ? 
sd. There was an iron stove in the room, could it be that 
this was subject to a periodic encrease and decrease of mag- 
netic power ? 
