568 
Proceedings of the Royal Society 
by several philosophers.* But, so far as we know, the effect of 
flame on the electric spark has not been methodically observed, or 
at all events has not been methodically measured. This was the 
problem which at the opening of the College session presented 
itself to us, and the results now attained by a course of experi- 
menting appear capable of throwing some light on the solution. 
We first made a number of tentative experiments, for the purpose 
of finding out the general aspect of the phenomena, and the con- 
ditions most favourable for exact measurement. An ordinary 
Bunsen burner served to supply a flame luminous or nonduminous. 
It was always connected with the earth, and the charged body was 
in general a disc of 4 inches diameter, connected along with a large 
Leyden jar to the insulated conductor of a Holtz machine. We 
tried the disc in a position above the flames, but found that the 
disturbing conditions introduced were, as was to be expected, 
rather numerous, namely, the heating of the disc and the covering 
of it with soot, and the melting of the gutta-percha covering of the 
connecting wire. Hence for a series of measurements we preferred 
the disc placed in a position at the side, as represented in the 
accompanying figures. (See Plate IY. a). 
The series of observations finally attained are recorded in Tables 
I. and II. ; they are supported by the more preliminary observa- 
tions. The charged disc was throughout placed at the side of the 
Bunsen tube in a vertical plane, and so as to have its centre on the 
same level with the mouth of the tube. The conditions varied 
were — first , the nature of the flame ; second , the sign of the charge 
on the disc ; third, the height of the flame ; fourth , the distance of 
the disc from the tube. As regards the first variation two states 
were observed, the one being the clear flame without any luminosity, 
the other being the flame as luminous as possible. The height of the 
flame was varied through a range from 1 cm. to 8 cm., but sometimes 
the range was extended to the maximum height of the flame (about 
20 cm.). In the case of the non-luminous flame, it was the 
height of the apex of the cone that was measured off ; while in the 
case of the luminous, it was the extreme tip. The total height of 
the former flame may be taken as double that of the cone. The 
* A summary of what has been done is given in a recent paper by Holtz, 
Carl's Rcpcriorium , vol. xvii. p. 269. 
