Naturdl PhUosopliy-^EUctrlcity. 203 
effect may be produced, by turning up the ends of the branches, 
and fixing to them a plate or piece of metal, upon which they 
may stand* 
ELECTRICITY. 
17. Pyto-Electrkity of the Tourmaline. — The electricity of 
this mineral may be shewn in a very satisfactory and beautiful 
manner, by means of a thin slice taken from any part of the prism. 
In order to perform the experiment to most advantage, the slice 
should have its surfaces perpendicular to the axis of the prism. 
It must then be placed upon a piece of well polished glass, and 
the glass heated to a considerable degree. At the proper tem- 
perature, which is about that of boiling water, the slice will ad- 
here to the glass so firmly, that even when the glass is above 
the tourmaline, the latter will adhere to it for six or eight hours. 
By this means slices of a very considerable breadth and thick- 
ness develope as much electricity as is capable of supporting 
their own weight. The tourmaline adheres also to all metallic 
bodies, to wax, and all minerals that have been tried. 
Mr Sivright has fitted up a tourmaline, so as to bring the ac- 
tion of its two poles very near to one another. It resembles 
the letter 17, with an opening in its curved part. The straight 
part represents the tourmaline, and the two curved parts 
are pieces of silver- wire rising out of two silver caps, one of 
which embraces each ‘pole of the tourmaline. When a pith 
ball is suspended at the opening between the extremities of the 
wires, it will vibrate in a very beautiful manner, in virtue of 
their opposite actions, ^pinus fitted up the tourmaline in a si- 
milar, but less elegant manner, than the preceding. Sir Hum- 
phry Davy has stated, ( Elements of Chemical Philosophy, vol. i. 
p. 130), that when the stone is of considerable size, flashes 
of light may be seen along its surface.*” We shall be obliged 
to any of our readers, who have large enough tourmalines, if 
they will attempt to verify this observation. 
18; Pyro-Electricity of Nadelsteim — When the Abbe Ilaliy 
discovered the developement of electricity in the Mesotype by 
means of heat, the two substances called Apophyliite and 
Nadelstein, were comprehended under the name of Mesotype, 
the former being the Mesotype epolntte, and the latter the Meso- 
type aciculaire of that mineralogist. Haiiy does not appear to 
