324 Mr. J. N. Heavder 07i a new Instrument for Registering 



be transformed into a function of p by means of the equations 

 (25) : this done, and the integration effected, (36) is evidently 

 the equation of the curve (25), when the cone upon which it is 

 conceived to be described is unfolded into a plane. Again, if by 

 means of (26) we eliminate p from the equation 



« +« - p^ + p^'dd^' 



the latter will become the differential equation of the plane 

 curves whose elements attract the pole in the same manner as 

 the corresponding elements of (26), — u being the reciprocal of 

 the radius vector r. If we suppose 



nr,e,c)=0 (27) 



to be the general integral of this equation, where e is the arbi- 

 trary constant, then the equations of the system of curves of 

 double curvature, whose elements attract the pole in the same 

 manner as the corresponding elements of the given curve (25), 

 will evidently be the result of the elimination of p and 6 from 

 the four equations (25), (26) and (27). 

 Pan, March 1857. 



XLV. On a new Instrument for Registering a rapid succession of 

 Electrical Discharges, and a comparison of the Effects of the 

 Induction Coil with those of Frictional and Hydro-electric 

 Machines. By Jonathan N. Heakder, Mechanician, Ply- 

 mouth^. 



THE induction coil appears to be an instrument so susceptible 

 of extension of power, modification to suit requirements, 

 and practical application to the most important purposes, that 

 experiments calculated to throw light upon its action or develope 

 its capabilities are invested with more than ordinary interest. 

 Without in the slightest degree wishing to detract from the 

 merit so justly due to M. Ruhmkorff, for having first elicited 

 the latent powers of this instrument and exhibited its capabilities 

 by an extension of principles already known and practised, I may 

 venture to express a little surprise that the ingenuity which con- 

 trived the instrument did not still further display itself in its 

 subsequent improvement. If, as was stated, however, by Mr. 

 Gassiot on the occasion of a lecture which I had lately the honour 

 of delivering before the SocietyofArts,M. Ruhmkorff was actuated 

 more by a desire to make a cheap than a perfect machine, the 

 fact is easily accounted for. The mode of insulation which he 

 has adopted, viz. that of covering the wire with cotton and sepa- 



* Communicated by the Author. 



