108 Mr. <jh Fuller on a small Electrical Machine. 



oxygen. At the temperatures employed in the foregoing 

 researches, however, it is not to be supposed that dissociation 

 would proceed to completion ; this change, therefore, would not 

 have taken place. 



But further experimental investigations must precede the 

 theoretical discussion of this question. It will be my first 

 endeavour to carry out experiments within greater temperature- 

 limits, and especially to estimate the specific heats of the 

 vapours. I have already carried out a prolonged series of 

 preliminary experiments with this object, making use of the 

 apparatus already described with a few slight modifications ; 

 the narration of these experiments will occupy a further com- 

 munication. 



XIII. Model of a small Electrical Machine. 

 By George Fuller, C.E., Belfast*. 



THIS machine is a double-acting electrophorus worked by 

 cranks, with the addition of an arrangement by which a 

 small electric charge given to it is augmented and kept up, so 

 that the dielectric does not require to be recharged. 



A is a vulcanite plate supported in a vertical position by two 

 insulated standards, p, p. 



B, W are two insulated metallic plates, one on each side of 

 the plate A ; these can be moved together to and from con- 

 tact with A by means of cranks worked by the handle C. 



m and n are two conductors armed with needles and con- 

 nected by means of two glass rods, so that they receive the 

 same reciprocal motion from the mechanism by means of the 

 wire, cord, and pulleys, g, g, g. The wire g is attached to the 

 arm that moves the plate B' ; and the length of the cord and 

 size of pulley are so adjusted that when this is in its extreme 

 position from A, as shown, m and n are also at one extremity 

 of their motion, as shown ; and when B and W are in contact 

 with A, m and n are horizontal. The conductor n is not insu- 

 lated ; and it will be seen by the diagram that m and n during 

 their motion pass on either side of the plate A. 



To the conductor m is fixed a wire terminating in a brass 

 ball, d ; this wire is of such length and form that when B and 

 W recede from A, and m and n move downwards from their 

 horizontal position, the ball d passes close to W. Care has to be 

 taken that this juxtaposition does not occur until the vulcanite 

 plate separates the points on m and n. 



The action of the instrument is as follows : — A charge of, 



* Communicated by the Physical Society. 



