10 On a new Form of Air Leyden, $c. [June 2, 



W, dipping in the water in which the cable is submerged, and 

 with the case C of the mnlticellnlar, and with the case and 

 plates A of the leyden, and with a fixed stud, S, forming part of the 

 operating key to be described later. The other end of the voltaic 

 battery is connected to a flexible insulated wire, FFF, used for 

 giving the primary electrification to the insulated wire J of the cable, 

 and the insulated cells II of the multicellular kept metallically 

 connected with J. The insulated plates, B, of the leyden are 

 connected to a spring, KL, of the operating key referred to above, 

 which, when left to itself, presses down on the metal stud S, and 

 which is very perfectly insulated when lifted from contact with S by 

 a finger applied to the insulating handle K. A second well insulated 

 stud, S', is kept in metallic connection with J and I (the insulated 

 wire of the cable and the insulated cells of the multicellular). 



To make a measurement the flexible wire F is brought by hand to 

 touch momentarily on a wire connected with the stud S', and imme- 

 diately after that a reading of the electrometer is taken and watched 

 for a minute or two to test either that there is no sensible loss by 

 imperfect insulation of the cable and the insulated cells of the multi- 

 cellular, or that the loss is not sufficiently rapid to vitiate the 

 measurement. When the operator is satisfied with this he records his 

 reading of the electrometer, presses up the handle K of the key, and 

 so disconnects the plates B of the leyden from S and A, and connects 

 them with S', J, I. Fifteen or twenty seconds of time suffices to take 

 the thus diminished reading of the multicellular, and the measurement 

 is complete. 



The capacity of the cable is then found by the analogy : As the 

 excess of the first reading of the electrometer above the second is to 

 the second, so is the capacity of the leyden to the capacity of the 

 cable. 



The preceding statement describes the arrangement which is most 

 convenient when the capacity of the cable exceeds the capacity of the 

 leyden. The plan which is most convenient in the other case, that is 

 to say, when the capacity of the cable is less than that of the leyden, 

 is had by interchanging B and J throughout the description. In this 

 case, a charge given to the leyden is divided between it and the cable. 

 The capacity of the cable is then found by the analogy: As the 

 second reading of the electrometer is to the excess of the first above 

 the second, so is the capacity of the leyden to the capacity of the 

 cable. 



A small correction is readily made with sufficient accuracy, for the 

 varying capacity of the electrometer, according to the different posi- 

 tions of the movable plates, corresponding to the different readings, 

 by aid of a table of corrections determined by special measurements 

 for capacity of the multicellular. 



