322 



HISTORY OF SCIENCE. 



appeared hopelessly.intricate and inexplicable to be expressed and ar- 

 ranged in a simple and systematic manner. Gray repeated, in his turn, 

 many of Du Fay's experiments, and he especially describes the lumi- 

 nous appearances and the electrification of water. In connection with 

 the subject of the "electric fire," he makes the remark (1735) that se- 

 veral of the experiments appear to indicate that it may be of the same 

 nature as lightning. 



Germany took a part in the development of the new science by 

 devising improvements on the electrical machine. The progress of 

 any natural science is, we shall constantly see, greatly dependent upon 

 the perfection of the appliances by which its phenomena are studied. 

 Conductors were provided by which the electricity might be gathered 



from the revolving globe of glass, 

 and a cushion was substituted for 

 the hand. About 1750, cylinder 

 machines were constructed in Eng- 

 land and in Holland ; but soon 

 after this, machines upon an en- 

 tirely new plan were made by 

 RAMSDEN, who substituted a cir- 

 cular plate of glass for the globe 

 or cylinder; and the most com- 

 monly met with electrical machine 

 at the present day is that of Rams- 

 den. The form of this, represented 

 in Fig. 157, is too well known to 

 require description. In the earlier 

 globe machines the " conductor " 

 was simply a metallic bar or tube 

 suspended by silk cords, with one 

 of the ends nearly touching the re- 

 volving globe. This arrangement 



is shown in Fig. 154. WILLIAM WATSON, who wrote on electricity 

 about the middle of the eighteenth century, gives in his work the view 

 of the machine shown in Fig. 158, which represents, he says, an elec- 

 trical machine much used in Holland, and especially in Amsterdam. 

 This may be compared with the machine constructed many years after- 

 wards by NAIRNE, a view of which is given in Fig. 159. c is a cylinder 

 of glass^ D and D' are hollow metallic cylinders with spherical ends, 

 and each is supported on a glass pillar. To D is attached a cushion 

 pressing against the cylinder, and D receives the electricity from the 

 glass by a number of projecting metallic points placed on the side 

 next the cylinder. This machine permits both resinous and vitreous 

 electricity to be studied, for while the conductor D supplies vitreous 

 electricity, the conductor D' yields an equally ready supply of resinous 

 electricity. This form of the electrical machine illustrates another 



FIG. 157. THE PLATE ELECTRICAL 

 MACHINE. 



