438 Chronicles of Science. [July, 



of thallium and mercury. Pure thallium is electro-positive to 

 amalgamated thallium. These experiments prove that the position 

 of thallium is much lower than that which separates cadmium from 

 zinc in the Daniell's couple. They confirm this general proposition 

 — " Every time that a metal is united to mercury, the place which 

 it occupies in the scale of affinities is modified, and thermo-phe- 

 nomena are observed." 



Experiments on the elevation of temperature produced by the 

 galvanic current have led M. E. Edlund to suppose that the 

 current by a special action independent of that of heat, causes an 

 expansion of the conductor which it traverses. He has therefore 

 instituted experiments on that subject, and the result is, that the 

 expansion is perfectly definite. The method adopted is as follows : 

 He takes a metallic wire 1*184 metres in length, the amount of 

 whose expansion by heat is known with perfect exactitude, and 

 passes a current through it. The wire is stretched horizontally 

 between a fixed clip and another working as a lever round a hori- 

 zontal axis, bearing a mirror, and the measurement of the elongation 

 of the wire is effected by observing the angular displacement of the 

 mirror. If the temperature of the wire at the moment of observa- 

 tion be known, it will be seen whether its elongation accords with 

 this temperature or not. To measure this temperature, M. Edlund 

 measures the electric conductivity of the wire, and deduces the 

 temperature from it. Now by this method he always finds a lower 

 temperature than that which would correspond with the observed 

 elongation, from which it follows that an elongation takes place in 

 the wire independently of the action of heat. The conductivity 

 is measured by the method of Wheatstone's Bridge. The rheostat is 

 composed of two German-silver wires stretched upon a horizontal 

 board. To determine the relation between the temperature and 

 resistance, the wire is rolled round four glass pillars fixed in a 

 wooden disc, and the cylinder formed by the wire placed in a glass 

 vessel containing thermometers, and immersed in a bath the tem- 

 perature of which was varied. The author gives details of several 

 experiments, and concludes by stating that the current produces in 

 the solid bodies which it traverses an expansion independent of that 

 of heat ; and although these investigations are not sufficient to make 

 known the law of this expansion, they show that it increases rapidly 

 with the intensity of the current, and also that this action does not 

 cease immediately on the cessation of the passage of the current 

 through it, but disappears by degrees. 



Professor De la Eive has published an elaborate series of 

 experiments on the propagation of electricity in highly rarefied 

 elastic fluids ; he finds that the transmission of the electric discharge 

 through rarefied gases is accompanied by a sensible elevation of 



