228 Mr. Christie on magnetic 
I now proposed observing the effect on the terminal arc of 
a change of temperature, and consequently a change of inten- 
sity in the needle, other circumstances remaining precisely 
the same. For this purpose, I plunged the ends of the needle 
nearly to its centre into boiling water, and vibrated it as soon 
as possible afterwards. On my first doing this the pivot on 
which the needle vibrated was slightly injured, so that being 
obliged to re-magnetise the needle, in order to obtain results 
previous to a diminution of intensity to be compared with 
those after the needle had been immersed, these results could 
not be compared with those which I had before obtained. I 
mention this, to guard against any conclusions being drawn 
from a comparison of the times of vibration or of the terminal 
arcs in the following observations with those of the preceding. 
In consequence of the increased friction on the pivot, the arc 
of vibration was reduced to on each side of zero at the 
30th vibration, I therefore only observed that number : the 
vibrations commenced, as before, 90° from zero. 
arc of vibration to a certain extent was, by heating the disc, increased from being 
less than 23 to 26 1 , taking a mean of several observations. The method of vibrat- 
ing metallic discs between the poles of a magnet, which I here made use of, was, I 
believe, first employed by Mr. William Sturgeon, of Woolwich, for the purpose 
of exhibiting the magnetic properties of different metals, which it does in a very 
Striking manner. 
