EARTH TREMORS. 311 



the stone support was magnified 50,000 times. In 

 several ways the apparatus was insulated from all accidental 

 disturbances. The spot of light was observed from 

 another room by means of a telescope. This instrument 

 was so delicate that even at the distance of sixteen feet 

 the shifting of your weight from one foot to the other 

 caused the spot of light to run along the scale. So 

 sensitive was. the instrument that, notwithstanding its 

 being cut off from the surrounding soil by a trench filled 

 with water and the whole instrument being immersed in 

 water to damp out the small vibrations, it would seem 

 that the ground was in a constant state of tremor ; in fact, 

 so persistent and irregular were these movements that it 

 seemed impossible to separate them from the perturbations 

 due to the attraction of the moon.^ 



As a result of observations like these, the world had 

 gradually forced upon it the fact that the ground on 

 which we live is probably everywhere in what is practically 

 an incessant state of vibration. 



This led those who were interested in the study of 

 earth movements to establish special apparatus for the 

 purpose of recording these motions with the hope of 

 eventually discovering the laws by which they were 

 governed. 



Experiments in Japan, — The simpler forms of appa- 

 ratus which have been used in Japan may be described 

 as delicate forms of seismoscopes, which, in addition to 

 recording earth tremors, also record the occurrence of 

 small earthquakes. 



A simple contrivance which may be used for the pur- 

 pose of recording small earthquakes can be made with a 

 small compass needle. 



If a light, small sensitive compass needle be placed on 

 * Rejwrts of British Association^ 1881. 



