368 RECENT PROGRESS IK PHYSICS. 



Tiiess, in a short paper, (Pogg. Ann., LXIX, 286,) says that the 

 memoir of Reich recalled similar experiments made hy himself as early 

 as 1844, among which he cites the following as particularly striking 

 and instructive : 



A platinum spoon, with a round mouth, holding 0.24 grammes of 

 water, was insulated and connected by a wire with Belirens and 

 Fechner's electroscope. The spoon was raised to a white heat hy a 

 spirit lamp placed beneath, the lamp rapidly removed, and a quan- 

 tity of solution of salt, nearly sufficient to fill the spoon, was then 

 introduced by a pipette. The liquid passed into the spheroidal state, 

 rotated, and, when the cooling had reached a certain point, was 

 thrown out of the spoon with violent ebullition. During the whole 

 course of this experiment no electricity showed itself. 



A strip of platinum foil was rolled into a cylinder seventeen lines 

 long and five in diameter, and placed over the cavity of the spoon : 

 the previous experiment was then repeated. On the violent boiling 

 of the fluid so much — E. was jjroduced that the gold leaf struck the 

 opposite j)ole. 



This experiment, which can always be repeated with the same 

 result if the surface of the i^latinum be previously freed from the salt 

 deposited, teaches us that in Pouillet's experiment the source of the 

 electrical excitement is not in the chemical separation brought about 

 by the evaporation, but in the friction of the finely divided particles 

 of fluid upon the sides of the vessel, provided that the fluid rolls over 

 the sides without wetting them. 



By slow evaporation Iliess could never obtain a trace of electricity, 

 neither could Reich develope any by evaporation under the boiling 

 point. 



All of the experiments which Reich made to discover a possible 

 development of electricity by the condensation of steam gave uni- 

 formly negative results. 



Riess also repeated Fouillet's experiments on the development of 

 electricity by the process of vegetation. An insulated porcelain vessel 

 was filled with loam, and cresses sowed in it. The earth, always kept 

 moist, was connected by a brass wire with the collecting plate of a 

 six-inch condenser. The condensing plate, when raised, was tested 

 by a pile electroscope. From March until April, 1844^ Riess caused 

 cresses to germinate eleven times, examining the condenser daily 

 until they had reached the height of two inches. Traces of electricity 

 were often found, but not of a constant kind. Some check experi- 

 ments, with earth alone, made it probable that even these traces did 

 not arise from the vegetation. 



From all of these experiments, it follows that the opinion, that in 

 evaporation and in the p)roccss of vegetation are to he found the sources 

 of atmospheric electricity, is altogether without experimental foundation. 



§ 11. The electrical machine. — The electrical machine belongs to 

 the most common and best known of physical apparatus, and yet 

 powerful machines can rarely be obtained at a moderate price. On 

 this account, I think it will be interesting to many to learn the mode 

 of construction according to which Caii Winter (electrician, &c., Wie- 

 den, Waaggase No. 501, Vienna) makes machines of excellent per- 

 formance and at a very reasonable price. 



