540 Mr. P. E. Shaw on 



leverages by clamping them in different positions. The 

 greatest leverage thus obtainable was about 1000 : 1, and the 

 least about 100 : 1. A centimetre-scale was marked on the 

 levers, so that the clamps could be brought to any desired 

 position as often as required. 



The arrangement for holding the telephone-receiver, on 

 which the experiments are made, will be described next. 



There is a massive hollow cylinder of wrought iron 15 cm. 

 long, 9 cm. diameter, the metal being about \ cm. thick, 

 The telephone-receiver is screwed to a ring on the further side 

 of the cylinder, so that, on looking from the back, the whol^ 

 diaphragm may be seen. There is also a screw cut on the 

 outside of the cylinder, which works in a screw cut in a ring 

 of iron, imbedded in, and screwed to, the wooden frame. 



A lock-nut is provided so that when the cylinder has been 

 screwed into position it may be tightened and held rigid. 



By having such a massive and well-fitting support for the 

 receiver, firmness and ready adjustability are secured for it. 



Having briefly described the essential parts of the appa- 

 ratus, we now proceed to consider the various adjuncts 

 separately. 



2, Supports. 



The table is supported from the foundation of the building 

 by brick piers. Vibrations passing through to the table 

 would be mostly of high frequency, and so should not be 

 transmitted by a succession of heavy masses separated by 

 springs and layers of indiarubber. The series was as fol- 

 lows : — (1) Blocks of solid pure rubber on the table; (2) a 

 lead slab of 180 lb.; (3) four soft rubber balls; (4) a board 

 weighted to 50 lb.; (5) four soft rubber balls; (6) the large 

 rectangular frame loaded from which hang (7) four rubber 

 springs which hook on to (8) the apparatus, which is loaded 

 to about 50 lb. 



The above provisions against tremors were sufficient for the 

 most delicate work, provided that no violent vibrations were 

 started in the neighbourhood. The motion of carts in the 

 streets, violent wind-gusts, or the working of near factory- 

 machinery were fatal. 



An attempt was made to find roughly the efficiency of the 

 various layers in the series, as follows. I found the vibration 

 amplitude in the apparatus (1) when all the layers were in, 

 (2) when the upper one was removed, (3) when two were 

 removed, and so on. By actual measurement the amplitudes 

 were found to be roughly (using jj,/j. as unit) : — 



1, 10, 15, 40, 100; 



