12 Mr. Christie on the effects of temperature on 
by the terrestrial forces and those of the magnets, slightly 
agitating the needle, that it might the more readily assume 
the true position ; from this it was led, by means of a very 
small and weak magnet, held on the outside of the compass- 
box, towards the easterly point of equilibrium, which was 
observed in the same manner ; and from this it was led in 
the same way towards the southerly point, which, however, 
was not observed with an intention of deducing any thing by 
means of the equation (a ) , which was not calculated for such 
a value of q>. After these observations of the points of equi- 
librium, the temperature of the south magnet being observed, 
the time set down in the seventh column, at which the ob- 
servations concluded, was noted. The temperature of the 
water in the pans was now increased or diminished, accord- 
ing to circumstances, by the addition of other water, and the 
pans covered over, to prevent any rapid changes of tempera- 
ture during the observations : after allowing a short time for 
the magnets to acquire the temperature of the water, the 
observations were repeated. To prevent any ambiguity, 
with regard to the time indicated being morning or evening, 
I have, except when otherwise expressed, adopted the astro- 
nomical division of the day, from noon to noon. The scale 
made use of for the temperature was in all cases that of 
Fahrenheit. 
s 
