-2 Mr. Christie on the effects of temperature on 
a greater extent, in the scale of temperature, than was neces- 
sary for the object which I had at first in view. In consequence 
of this, and the length of the calculations into which I have 
been obliged to enter, the accomplishment of my purpose 
was delayed for a considerable time, and continued indispo- 
sition has since prevented me, until now, completing the 
arrangement of the tables of results. 
In the present paper, I propose to detail the experiments 
which I made in order to determine the effect of changes of 
temperature on the forces of the magnets, to the extent to 
which I observed their temperature to vary, during my 
observations on the diurnal changes in the direction of the 
needle, when under their influence ; to apply the results 
which I obtained to the correction of the observations them- 
selves, thereby accounting for the apparent anomalies noticed 
by Mr. Barlow and myself, in the observations made in 
doors and in the open air ; and by means of these corrected 
observations, to point out the diurnal variations in the ter- 
restrial magnetic intensity. 
It had been my intention to determine purely from obser- 
vation the portion of the arc of deviation due to the changes 
which I noticed in the temperature of the magnets ; but I 
found that this depended so much on the situation of the 
point at which the needle was held in equilibrio by the ter- 
restrial forces and those of the magnets, that it would hardly 
be possible to determine how much of this portion was due 
to the extent of the change of temperature, or the degree of 
temperature where the change took place, and how much to 
the azimuth of the needle, when affected by this change. I 
was therefore under the necessity of having recourse to 
