4 Mr. G. Gore on the Development of Dynamic Electricity 



contain the liquid ; it is filled by means of tbe bent glass tube B. 

 The ends of the cylinder are closed by perfectly similar plates of 

 metal, C, C, varying in thickness from j'^th of an inch with 

 flexible metals, such as copper, silver, platinum, or aluminium, 

 to ytjth of an inch with brittle metals (such as bismuth or anti- 

 mony), each of which, if of flexible metal, has a short projecting 

 arm D, and wire or strip E (soldered or riveted to the arm), of 

 the same metal, for connecting with the galvanometer; and if of 

 brittle metal, has a narrow taper rod or arm of the same metal, 

 varying from 10 to 15 inches long (according to the thermic 

 conductivity of the metal), projecting from one part of its edge, 

 with a connecting wire attached for the same purpose ; the object 

 of having the arms so long, and of having an arm to each plate, 

 is to prevent the heat applied to the upper plate extending to its 

 junction with the connecting wire, and causing an interfering 

 thermo-electric cm-rent ; also to allow of the plates being inter- 

 changed occasionally. 



8. F is a thin cylinder either of glass or metal (the former T 

 have used, but it is apt to be broken by the pressure), open at 

 both ends, of the same depth and internal diameter as the lower 

 cylinder, and with an external flange |th of an inch wide upon 

 its lower end. There are suitable washers of vulcanized india- 

 rubber interposed between the metal plates and the ends of the 

 cylinders, in order to make the two vessels water-tight. In some 

 instances, when using plates of cast metal, such as bismuth or 

 antimony, I have had the outer or open cylinder cast in the same 

 piece of metal as the plate; and with sheet copper plates I 

 have sometimes formed the cistern of sheet copper and soldered 

 it to the back. G G is a circular plate of flint-glass |ths of an 

 inch thick, with a round bevelled hole in its centre to receive 

 the cistern ; and H H is a circular plate of brass |ths of an 

 inch thick, with a round hole of the same size (but not bevelled) 

 in its centre ; it is covered on its upper surface with a thin sheet 

 of vulcanized india-rubber. 



9. The two circular plates are held together and embrace the 

 cylinders, washers, and metal plates firmly, by means of four 

 thumb-screws (with "quick threads") passing freely through 

 holes in the plate of glass and screwing into the lower plate, of 

 which only two, 1 1, are shown in the figure; washers of vulcan- 

 ized india-rubber are interposed against those plates to equalize 

 the pressure; there are also gutta-percha washers against the 

 heads of the screws. A small band of vulcanized india-rubber, 

 with a metallic hook at each end, is sometimes used ; it passes 

 over the supply tube at B, and hooks upon two of the screws to 

 keep the tube secure ; but generally this is unnecessary, the tube 

 being fitted to the hole in the cylinder by grinding and fixed by 



