394 Mr. J. N. Hearder on the Amount of Electricity developed 



Although any separation of the silk flap from the cylinder in 

 a direction across its length and parallel to the rubber is inju- 

 riousj yet the folds which form in the silk in the direction of its 

 length, from the rubber to the conductor, do not, unless they 

 ai'c very large, materially interfere with the action of the ma- 

 chine ; in order to avoid these, however, the silk flap may be slit 

 in one or more places, longitudinally through its whole length 

 if necessary, thus forming it into several long and narrow flaps, 

 whose edges will occasionally overlap ; the flap will thus lie much 

 smoother, and will improve the action of the machine. If, how- 

 ever, the irregularity of the cylinder be such as to cause these 

 edges to recede from each other during its rotation, it would be 

 better to put the silk fla]) on in separate strips of 3 or 4 inches 

 wide, allowing their sides to overlap each other half an inch or 

 more. The great desideratum is close proximity of the flap 

 with the cylinder. 



To ascertain the influence of the flap over the excitation, a 

 cylinder was fitted, having a flap so contrived as to allow of its 

 being shortened to any extent without interfering with the 

 foregoing conditions. The conductor was mounted with a sliding 

 curved arm, which carried the collecting points, and allowed of 

 their being placed just in advance of the termination of the silk 

 flap. The Leyden jar and discharger were attached to the con- 

 ductor, and the striking interval was adjusted to the desired 

 length ; the circumference of the cylinder was 23-5 inches, and 

 the length of the rubber 7| inches, the surface rubbed at each 

 revolution thus being 17G'25 square inches. The efitcts of the 

 diff'erent lengths of silk flap were as follow : — 



Length of silk flap Number of turns Amount of surface 



It will thus be observed that very little increase of effect was 

 obtained with more than 4 inches of silk flap, which quantity, 

 with the width of the rubber, altogether about 5i inches, em- 

 braced about a quarter of the circumference of the cylinder. It, 



