19 
the intensity of magnetic forces ^ &c. 
same corresponding hours of the day, the motion in both 
instances being equally distinct, regular, and progressive/'* 
These anomalies, I also noticed, although, as I have men- 
tionod in my former paper, I did not find the reversion, in 
the directions in the two cases, to take place with the same 
regularity and uniformity that Mr. Barlow observed it to 
have. In that paper I also stated my opinion, that these 
anomalies had arisen from the diffefenr.e in the changes of 
temperature in the magnets when in doors and when in the 
open air, and that the observations in the two cases would be 
found to agree when they were freed from tlie influence of 
difference of temperature in the magnets. 
As I had already made observations in doors, in which I 
noted the temperature of the magnets, it was now my intention 
to make corresponding observations in the open air, in order 
that by reducing the obervations to the same standard of tem- 
perature, their agreement or disagreement might be put be- 
yond doubt. For this purpose the whole apparatus was placed 
in my garden, exposed to the sun and air, on a table having 
its legs driven firmly into the ground ; and for several days 
I observed, at stated intervals, the positions of the points of 
equilibrium ; when I had an opportunity I also made experi- 
ments, similar to the preceding, for the purpose of determin- 
ing the value of A j^, to be applied to the correction of the 
observations in doors and in the open air. 
On adjusting the magnets to the needle, I again found that 
* In the Postscript to this paper, Mr. Barlow, to whom I had communicated 
my views with regard to the effects of temperature, refers to the experiments which 
I had made, for the explanation of these apparent anomalies. 
