256 Electrical Machines. 



with the great mass of electricians of this time, as well as his contem- 

 poraries, he has overlooked a real cause of deterioration. I allude to 

 the imperfect conducting power of cushions, made as they are usu- 

 ally, of silk, or leather stuffed with hair, or other nonconducting sub- 

 stances. The desiccation of the cushion and other parts of the rub- 

 ber, may counteract the benefit otherwise produced by any increase 

 of aridity in the surrounding medium. 



By stuffing the cushions with the elastic iron shreds scraped off 

 from weaver's reeds in manufacturing them, and making a commu- 

 nication between the shreds and the steel spring supporting the cush- 

 ion and attached to the negative conductor, I have seen the sparks 

 yielded by a machine more than trebled in length, and frequency. 



As a coating for the cushion upon the whole I find the aurum mu- 

 sivura, more efficacious than the amalgam usually employed, which 

 is apt to adhere to the glass, and promote the passage of sparks from 

 collecting points of the positive conductor to the cushion. I ques- 

 tion if the amalgam does not owe its efficacy to its conducting pow- 

 er, which tends to compensate the absence of this property in the 

 cushion. 



In speaking of experiments performed by means of electrical ma- 

 chines, the poles and conductors may in general be treated as synon- 

 ymous; yet strictly the poles are those parts of the conductors, or 

 conducting surfaces in connexion with them, between which the dis- 

 charge takes place ; so that when insulated metallic rods, however 

 long, are each at one end in contact with the conductors of the ma- 

 chine, the poles may be at the other ends of the rods. This view 

 of the subject is generally recognized in the case of Voltaic series, 

 which not being terminated by conductors, in the technical sense 

 used in speaking of the machine, gives rise, in this respect, to less 

 cause of misapprehension. 



I conceive it an error to suppose that the association of a large 

 conductor with a machine, contributes to the intensity of the sparks. 



It appears to me to render the sparks shorter, and less frequent, 

 though otherwise larger. 



