412 Dr. ingenhousz’s Account of a 
As the pifton could not reach to the extremity of this 
conical hollow (which confequently muft be always 
filled with common air), I defired him to fix to the pifton 
an ivory cone, through which the two wires would pafs 
to meet one another at the furface of the cone, leaving 
an interftice between them of about one line, through 
which the electrical fparlc fhould leap and fet fire to the 
air. This ivory cone fhutting up exactly the whole ca- 
vity of the air box, no air could come into it but what 
was drawn in by the pifton. 
The piftol thus fitted up anfwered tolerably well. 
The figure joined to it will ferve to give a better idea of 
the whole contrivance than could be well explained by 
words. The fcale is in the proportion of one third of 
the real fize. 
The cone, inftead of ivory, may be made of folid 
glafs, which is a better non-conductor than ivory. The ca- 
nals in the ivory, through which the two wires pafs, may 
be made wide enough to contain a glafs tube, through 
which the wires pafs ; or to be filled with a non-condu£t- 
ing cement, as fealing wax, for the fame purpofe. The 
cone may even be made of brafs, provided two glafs 
tubes are lodged in it, to give a paflage to the two wires. 
I kindle this piftol fometimes by putting in the touch- 
hole a little bit of a cotton thread foaked in moift gun- 
pow'der 
