478 ‘ REPORT—1904. 
bands of a Babinet’s compensator = 74, wave-length with a field strength (=H) 
of 24,300 C.G.S. units was obtained. After 13 hours the displacement had 
decreased by 50 per cent.; on the next day no traces of the phenomenon were to 
be found. 
Much more remunerative results were obtained with a solution of ‘ Bravais’s 
Tron’ obtained from a Heidelberg apothecary, e.g., with a solution (¢ = 1:0041) 
containing 0:295 per cent. Fe (=e). A displacement (=f) of ¢ A with a field 
strength (=H) of 4460C.G.S, units was obtained in a polarisation-tube length 
=/)=5:5 centimetres—a value which gave a specific magnetic double refraction 
(k) =0'89 x 10-8, 
Further, the author was able to confirm Majorana’s results that the phenomenon 
obeys the law 
B=k Hle. 
He found, further, that % decreased with the time: e.g., the last value given 
above was 12 per cent. smaller after a lapse of ten days. He could not find that 
shape of trough or previous shaking of solution had an influence on the result. 
Apparently the Merck ferric hydrate and the Bravais’s iron have not the 
same chemical constitution. 
Oddly enough, no solution of Fe(OH), that was in the Heidelberg Physics In- 
stitute during the course of above experiments showed traces of double refraction, 
when subjected to a sudden and quick motion, as previously found by Professor 
Quincke (Ann. d. Physik, 1902). 
Schmaus’s explanation of the suspension character of the solution is nothing 
more than Quincke’s ‘ Schaum-Theorie.’ 
6. An Experimental Verification of Newton's Second Law. 
By W. D. Eacar, M.A. 
Teachers of dynamics have recourse to the movements of the heavenly bodies 
for supplying the proof of Newton’s Laws; and Galileo’s work is as a rule 
neglected. As the average student of dynamics is not an astronomer, modern 
scientific methods seem to require something more tangible, and this paper de- 
scribes an attempt to supply it. The acceleration is measured by the wave-lengths 
traced on a moving trolley by a vibrating steel spring carrying a paint-brush. ‘The 
trolley runs down a plane of which the inclination can be varied, and the force 
down the plane is measured by the weight which, hanging over a pulley, will just 
permit the trolley to run down with uniform speed. The apparatus of the trolley 
and steel spring is described by Mr. W. C. Fletcher (Chief Inspector of Secondary 
Schools) in the ‘School World’ for May 1904. Mr. Fletcher used the same 
force with varying masses, The writer of the paper has adapted the method to 
the same mass moving under varying forces. 
7. Ona Modification of FitzGerald's Model of the Ether. 
By J. BuTLER BURKE. 
FitzGerald represented the mechanism of the electro-magnetic field by a 
number of parallel wheels connected with india-rubber bands passing round their 
circumferences, the wheels rotating round parallel axes. 
Thus, if one of the wheels rotates faster than the rest the bands round it 
become strained on one side and loosened on the other. This represents the state 
of polarisation, the opposite sides being in opposite states. 
If the axes are connected by strong springs instead of being fixed to a board, 
we have a model of an ether which transmits the ordinary electro-magnetic dis- 
placements, and at the same time behaves as an elastic solid, thereby transmitting 
longitudinal and another class of distortional waves. Such an ether, which would 
be slightly compressible, would, although approximately satisfying Maxwell's equa- 
tions, at the same time propagate longitudinal waves. These waves, if they exist 
