438 Prof. Fitzgerald on the Structure of Mechanical 
74-9 
74:8 
Tea i iat on. 147 
Sirip A \s ee 74-7 
if ” 746 
45 129072 «(4°75 tan. =a700 
73-7 
73°6 
BSR 73:5 
Sirip B | 580. gh eat 734 
25” Z 733 
533 = T2=4G-1 73:5, tan 8-38 
From 2nd we have 
AN. 50°2 + 3°66=13°7. 
From Ist and 3rd 
00°5 +461 , 3:'444+3°38 
B, + 
2 2 
Of course absolute agreement in so rough a test was not to 
be expected. The difference of about 3 per cent. here observed 
might easily be accounted for. I think Mr. Bidwell will 
admit that his theory would have predicted a different result 
of the comparison. 
Cambridge, U.S., January 19, 1885. 
=14°2. 
XLVI. On the Structure of Mechanical Models illustrating 
some Properties of the dither. By Prof. Grorce FRANCIS 
FItzGERALD, /’..S.* 
HE elements of which the model is constructed consist of 
pairs of wheels so geared together that when one of them 
rotates it causes the second to rotate in the same direction. 
The simplest way of effecting this is to connect them by a 
band, and this is sufficient for a one-dimensional model. Such 
a model may be constructed by fixing a number of wheels with 
their axes parallel and at right angles to a plane, and con- 
necting each wheel with its neighbours by elastic bands. This 
represents a nonconducting region of the ether. <A perfectly 
conducting region is one in which there are no bands, and a 
partially conducting region would be represented by the bands 
* Communicated by the Physical Society : read March 28, 1880. 
