and other Minerals when exposed to Heat. QW 
pected, proportional to the rapidity of the change of tempera- 
ture, which of course would correspond to the period at which 
the temperature was highest, but on the contrary rose gradually 
to a maximum, when the tourmaline was about half way cooled 
to the temperature of the apartment; then gradually diminishing, 
redescended to zero when it reached that point. This remarkable 
result M. Becaurret obtained by suspending the crystal hori- 
zontally by a fibre of silk under a glass cover, the temperature 
of the air in which he had the means of regulating ; he then ap- 
plied to the extremities of the crystal, wires from the opposite 
poles of a dry pile, and, counting the number of oscillations made 
by the tourmaline, deduced the intensity. 
The form of the experiment which I have contrived, and 
which bears out M. Becaurrex’s conclusions, gives the same re- 
sults with great elegance and simplicity, without attempting to 
indicate the precise temperature of the stone at any period, 
which, whilst the heat of the medium in which it is placed 
changes, can only be by M. Becqueret’s experiment an approxi- 
mation, since the interior of the crystal must at any moment 
have a different temperature from its surface. 
I employed a simple form of Cov- 
Loms’s electrometer, which I construct- 
ed for the purpose with little difficulty. 
A flat shaped bottle, AB, having a wide 
tubulature at C, was provided. Fitted 
to the neck is a tube D, plugged at top 
by a cork F, through which passes a tal 
’ = 
crooked wire f, for the purpose of re- 
gulating a fibre of raw silk, supporting 
the needle of gum-lac e, one end of 
which is terminated by the disk g of .— 
gilt paper. The object to beexamined ¢()== 
is introduced through the tubulature 
C, the disk having previously been 
D2 
