622 



SCIENCE. 



EXPERIMENTS OF M. BJERKNES. 



" inverse" imitation of electric and magnetic 

 by hydro-dynamic phenomena. 



It must be confessed that absolutely nothing is known 

 of the real nature of electricity. The principle of the 

 conservation of energy and that of the unity of physical 

 forces, which tends to simplify the phenomena and em- 

 brace them under one common term, for want of a clear 

 and precise definition lead us to consider electricity or 

 rather electric phenomena, as a mode of movement. This 

 conception removes the difficulty, simplifies the question, 

 but does not resolve it. The mode of movement, once 

 admitted, forcibly compels the abandonment of the idea 

 of fluid, which always accompanied electric phenomena 

 at the outset of their study. 



If we are agreed to-day upon the immateriality of elec- 

 tricity, we are, on the other hand, far from understanding 

 the nature of the special mode of movement which char- 



M. Bjerknes designates under the general name of 

 vibration, the movements which take, according to their 

 nature, the name of pulsation, oscillation, etc. 



Pulsation has reference to the change in volume. It 

 includes two phases, one, in which the body swells, the 

 other in which it shrinks. Pulsations are synchronous 

 when the phases commence simultaneously. 



Oscillation has reference to the change in place, it is an 

 alternative displacement to the right and to the left. 



M. Bjerknes mechanically obtains pulsations in water 

 by the aid of a very ingenious apparatus. 



The pulsations are produced by small cylinders stopped 

 at their ends by flexible walls. A small hand pump which 

 is partly shown on the right in fig. r, is employed to ex- 

 haust and compress alternatively the air in the cylinders 

 provided with flexible walls, at a great velocity. 



In the simplest pulsator, the two walls dilate and con- 

 tract at the same time under the action of forcing the air 

 from the pumps, the phrases are'synchronous (fig, 2. No. 

 i). In another arrangement, the two drums are sepa- 



Fig. I. Apparatus of M. Bjerk 



acterises electricity, the word being taken in its most 

 general acceptation. 



In his Rechcrches sur I ' electricite, M. Gaston Plante 

 expresses his ideas on this point in the following words : 



" Electricity can be regarded as a movement oi ponder- 

 able matter— movement of transportation of a very small 

 mass of matter incited with very great velocity, if the 

 question is of the electric discharge, and a very rapid 

 vibratory movement of the molecules of the matter, if the 

 question is of its transmission to a distance under the 

 dynamical form, or of its manifestation under the statical 

 form at the surface of the body." 



For some, who are much less precise in their definitions, 

 electricity is produced by molecular movements, without 

 otherwise determining its nature, characterised by form, 

 direction, velocity, periodicity, &c. 



In the experiments about to be described, M. Bjerknes 

 proposed to throw light upon the question of the nature 

 of molecular movements, by reproducing mechanically, but 

 INVERSELY, simple and fundamental electric phenomena 



nes at the Electrical Exposition. 



rated by a rigid wall, which forms two chambers each in 

 connection with a separate pipe conducting the air (fig. 2, 

 No. 2). We have thus a most complete system, for by 

 adjusting conveniently the tubes of the air-pump for ex- 

 hausting and filling, synchronous pulsation can be pro- 

 duced at will, as in the first case, or pulsation in which 

 the phases are alternate. 



Oscillations are produced by means ot small metallic 

 spheres bound to supports, upon which they oscillate, 

 under the action of compressed air, in a plane which 

 varies with the position of the sphere. 



Fig. 2 (No. 3) represents two of these oscillators, the 

 sphere on the right oscillating vertically up and down ; 

 that on the left, on the other hand, oscillates horizontally 

 from right to left. 



This is the very simple and well constructed apparatus 

 which M. Bjerknes employs. Now we come to the 

 phenomena. 



First two pulsatorsare taken and made to vibrate. The 

 phase of dilation, according to M. Bjerknes, correspo ds 



