20 Messrs. Henderson and Henry on the Motion 



water, becomes more conductive and its freezing-point 

 falls. The increase of conductivity is proportional to the 

 amount of water added. This law holds from 1 to 6 °/ of 

 water. Similar proportionality appears between fine freezing- 

 point and conductivity and between the freezing-point and con- 

 centration measured in per cents. 



The specific conductivity of anhydrous formic acid freezing 

 at 8°*52 is 1/5 . 10 -9 in terms of mercury at 8°*52, which 

 value agrees \evy well with the observations of Saposchnikoff. 



The molecular conductivity of anhydrous formic acid 

 freezing at 8°*52 is 32 . 10 -9 in terms of mercury at 8°*52. 



The temperature-coefficient, or the change of the conduc- 

 tivity in per cents, for 1°, is 0*020, and it is practically the 

 same for all solutions of water in formic acid up to 6 °/ . 



The relations can be written : — 



Specific conductivity at the temperature of freezing 



= 6*10-1- 10*546 (per cents, of water). 

 = 64*77— 6*937 (freezing-point). 

 Freezing-point = 8*52— 1*537 (per cents, of water), 



using the limits from above. 



My best thanks are due to Prof. J. J. Thomson who 

 supported me with his kind advice, and to Mr. W. C. D. 

 Whetham, who followed this work with the greatest interest. 



Cambridge, Cavendish Laboratory, 

 1896-97. 



III. Experiments on the Motion of the JEther in an Elec- 

 tromagnetic Field. By W. Craig Henderson, M.A., 

 B.Sc.', and J. Henry, M.A., B.E., 1851 Exhibition Science 

 Scholars *. 



AN electric wave when it passes through the aether pro- 

 duces a displacement current and a magnetic force at 

 right angles to this current ; there will thus be a mechanical 

 force acting on the aether in a direction at right angles both 

 to the displacement current and to the magnetic force, 

 which will therefore at some distance from the radiator be at 

 right angles to the front of the wave. If the oscillations are 

 not damped this force will be periodic and its mean value 

 zero ; it will, however, have a finite value if the oscillations 

 are rapidly damped. The following experiments were under- 

 taken at the suggestion of Professor J. J. Thomson to see 

 whether this force would set the aether in motion. 



* Communicated by Prof. J. J. Tbomson, F.E.S. 



