by equal surfaces of Cylinder and Plate Electrical Machines. 295 



however, showed that the flap had something to do with the 

 excitatiou of the electricity, either by increasing the distance ot 

 the collecting points from the rubber, and thereby preventing the 

 too ready return of electricity from the conductor m sparks to 

 the rubber, or by becoming itself an agent m the actual excita- 

 tion. ,, ^ 1 1 -i. 



Further experiments showed that the silk flap had its own 

 peculiar function, for when the machine was in good action, the 

 rubber could be withdrawn altogether from contact with the 

 cylinder, and the excitation would only gradually dimmish alter 

 a considerable number of turns; hence it would appear that the 

 rubber commences an excitation which the silk flap prolongs. 



The fact that there is no advantage gained by making the 

 silk flap extend over more than one-fourth of the circumference 

 of the cylinder, has enabled me to contrive a machine of double 

 power; for if the ordinary silk flap be cut so as to terminate on the 

 top of the cylinder, a second rubber may be introduced m the 

 place usually occupied by the prime conductor, having its silk 

 flap passing under the lower quadrant of the cylinder, and ter- 

 minating opposite to the edge of the upper flap. The prime 

 conductor in this case must be branched and placed opposite 

 the end of the cylinder with its two arms in a vertical direction, 

 extending one above, and the other below the cylinder; the 

 framework of the stand which supports that end of the cylinder 

 being made of a transverse bar and two uprights, placed at a 

 sufficient distance from each other to be beyond the influence ot 

 the lower branch of the conductor. If, however, the insulation 

 of the additional rubber be not required, the arrangement is 

 more simple, all that is necessary being to connect the rubber 

 with the machine by a curved spring reaching from one of the 

 unrights round the front of the cylinder to the other; in which 

 case, as the pillar, otherwise required to support the rubber, is 

 dispensed with, the conductor may still stand in front of the 

 machine, with its vertical branches embracing the cylinder, one 

 above and the other below. In this case the ends of the branches 

 must be fitted with transverse portions, of a length sufficient to 

 take the collecting points. A machine thus fitted will excite 

 twice as much electricity at each turn as one fitted with a single 

 rubber, the only disadvantage being, that the long zigzag sparks 

 will be rather shorter than with the single rubber, in consequence 

 of the greater ])roximity of the rubbers to the conductor, and the 

 greater facility of discharge thus afforded from the latter to the 

 former; but even this disadvantage is much diminished when 

 very large cylinders are used. 



AVith cylinders above 12 inches diameter, the advantage of the 

 foregoing arraugemcut is very great; for with the single rubber, 



