72 Scientific Intelligence. 



8. Chromophotography. — M. Marey, continuing his studies 

 upon the application of instantaneous photography to the investi- 

 gation of the motion of swimming animals, has devised a special 

 form of apparatus which he believes will prove of great utility in 

 experimental hydrodynamics. A tank is filled with water in 

 which is suspended a number of small bodies consisting of a mix- 

 ture of wax and rosin which are silvered. The density of the 

 water is then suitably modified by the addition of salt or other 

 substance, in order that the small bodies may be disseminated 

 throughout the liquid. The side of the tank has a backing of 

 black velvet and light is reflected into the water by means of 

 suitably placed mirrors thus illuminating the suspended particles. 

 Interesting reproductions of photographs are given. — Gomptes 

 Bendus, May 1, 1893, pp. 913-924. j. t. 



9. Reflection of Electrical Waves at the extremity of a 

 linear Conductor. — Mr. Birkeland points out the applicability of 

 Poynting's theories for the explanation of the resonance phenomena 

 discovered by Hertz. The electromagnetic energy in the field 

 surrounding the conductor moves in space in a direction normal to 

 the lines of electric force and magnetic force at each point. By 

 considering this theorem, Birkeland is led to an explanation of 

 multiple resonance, and to the various discrepancies between 

 theory and experiment noticed by those who have studied the 

 Hertz phenomena. — Comptes JRendics, April 17, 1893, pp. 803-806. 



J. T. 



10. Electrical Waves and light waves. — V. Bjerknes finds that 

 the extinction power of metals for electrical waves increases with 

 good conductors. It also increases with the magnetism of the 

 conductor. The swifter the electrical waves the less distance do 

 they penetrate into the conductor. The author points out various 

 discrepancies between the electromagnetic theory of light, the 

 ordinary theory, and believes that electrical waves represent the 

 motion of molecules as a whole, while the ordinary light waves 

 deal with the motion of individual molecules. He also believes 

 that a study of the action of very quick electrical oscillations on 

 magnetic molecules will fix a limit to the inertia ratio of an iron 

 molecule. — Ann. der Physik und Chemie, No. 4, 1893, pp. 592- 

 605. J. t. 



11. New Electrometers. — Bjekknes has described a new electro- 

 meter which he has used in his researches on Hertz phenomena ; 

 it consists of a thin plate of aluminum suspended at an angle 

 of 45° between thin plates of an air condenser. When the latter 

 are connected with the poles of a Ruhmkorf coil the aluminum 

 plate tends to set in the line of electrical force between the plates. 

 A simple formula connects the angle of turn of the plate with the 

 difference of potential of the terminals or plates of the air con- 

 densers. C. Christiansen suspends two plates separated by mica, 

 by suitable wire, between the plates of an air condenser. When 

 the latter are maintained as a certain difference of potential, the 

 suspended plates tend to turn so as to place themselves at right 



