154 Intelligence and Miscellaneous Articles. 



prove that it is posterior in age, not only to the Boulder- clay, but 

 also to the plateau-gravel capping the Middle Drift, by the time 

 necessary for the erosion of the deep valley in which it occurs. At 

 the same time he admitted the possibility of its being much older, 

 and intermediate in age between the Norwich Crag and the Chalk. 



XXII. Intelligence and Miscellaneous Articles. 



EXPERIMENTAL DEMONSTRATION OF THE ELONGATION OF A 

 CONDUCTOR TRAVERSED BY A CURRENT, INDEPENDENTLY OF 

 ELONGATION BY HEAT. BY E. EDLUND. 



H|^HE author was led, by experiments on the elevation oftempera- 

 JL ture produced by the current, to suppose that the current, by a 

 special action independent of that of heat, causes an expansion of the 

 conductor which it traverses. This phenomenon formed the subject 

 of an investigation on the part of this physicist, from which it 

 results that this expansion is real and measurable. 



His method is as follows : — Taking a wire the amount of whose 

 expansion by heat is known with perfect exactitude, a current is passed 

 through it, and its elongation is measured ; if its temperature at the 

 moment be known, it will be seen whether its elongation accords 

 with this temperature or is more considerable. 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 elonga- 

 tion takes place in the wire independently of the action of heat. 



The following is the series of operations performed upon each 

 wire : — 



The current is passed through the wire for a certain time, until the 

 total elongation has become constant : let U be this elongation — that 

 is to say, its increase of length relatively to that of the same wire at 

 a given temperature T. At the end of a very short time (0'36 sec.) 

 after the current has ceased passing, this elongation has diminished 

 by the quantity u ; and at this moment is measured the resistance, 

 which is designated by W. 



In the second place, the linear heat expansion of this same wire 

 is determined, and the value of the coefficient h is found. 



Lastly comes the determination of the relation between the resist- 

 ance and the temperature of the wire, which, as is well known, is 

 liable to vary within certain limits in wires of the same metal ; and 

 the numerical values are found for the equation which gives the 

 conductivity X by the formula 



X-100-a£+/3f-. 



Thus we have all the elements for calculating the excess of tem- 

 perature, T' — T, which the wire possesses at the moment when its 

 resistance W is measured, and, on the other hand, the excess T° of 

 this same temperature, supposing that the dilatation V—u is due 



