Notice of some New Electrical Instruments. 111 
a, is a glass tube which may be from six to twelve inch- 
es long; from an inch toan inch and a half in diameter, 
and from one twelfth to one eighth of an inch thick. It is 
desirable to have a tube of symmetrical bore. 4, is the pis- 
ton rod of some conducting substance. ¢, is the plug which 
serves for the rubber. ‘The plug is wound with silk cover- 
ed with amalgam. If the bore of the tube be uneven as it 
is in my instrument, the rubber may be filled with springs so 
as to adapt itself throughout. This trouble is unnecessary 
where a good tube can be obtained. d, is a glass rod or 
what is better a piece of thoroughly baked cedar wood cov- 
ered with shellac, at the end of which is a knob of cork, 
wood or metal, in which the collecting points are inserted 
in a radiating manner. As the piston passes up and down 
the tube, electricity is developed, and being collected by 
the points, is conducted by the chain to the hollow brass 
cap e, whence it may be received. ‘The cap e, is perforated with a 
number of holes to allow the air which is driven before the piston to 
escape. ‘Lhe instrument when worked must be held in a vertical 
position to allow the chain to fall and coil itself in the brass cap. This 
is a very convenient substitute for the electrophorus and is indeed a 
portable electric machine. From its construction it is well secured 
from moisture and dust and its power is quite sufficient for trying a 
number of experiments. It is particularly convenient in the detona- 
tion of gases, fulminating compounds, &c. The one which I have 
affords sparks about an inch long. In this case, the electricity which 
is developed by the upward stroke of the piston is collected. But 
a constant supply of electricity might be obtained by having collec- 
tors on both sides of the plug: in which case the piston rod should be 
covered with shellac, and the electricity be conducted through the 
plug by means of a wire covered with glass or shellac until it reach 
_ the chain.* 
There is another fact which I think worthy of communication. I 
discovered it accidentally about three years ago while I was witness- 
ing the attraction and repulsion of a figure made of pith of cornstalk. 
While it was moving backwards and forwards, a spark passed from 
the prime conductor through it to my hand, producing a singular and 
* This I contrived when at school five years ago. 
