Manchester Meinoirs, Vol. xlvi. (1901), No. 3. 13 



lines on the photographic plate, but apparently the 

 vibrations were too rapid, and the indications are too faint 

 to be reproduced. Fig. 8 represents what took place, 

 only, of course, the lines are less numerous and further 

 apart than in the experiment. At first, each turn of wire 

 would produce a photographic horizontal line, then, after 

 the release, as the pressure wave travelled upward, one 

 coil after another would move upwards at a uniform 

 velocity, would then remain stationary, and would then 

 move down, &c. 



SprinjT at rest moving up moving: down moving' up 



The diagram shows what happened, and the spring, which 

 1 will now release, will give an idea of the jerkiness of the 

 motion. 



The lower end of the spring can clearly be seen to 

 reverse its motion suddenly ; in fact, these reversals are so 

 sudden as to suggest hammer blows. At any higher point 

 one can see how the turns of wire are sometimes 

 stationary, sometimes moving up, sometimes moving down. 



The duration of a complete up and down travel of the 

 pressure in the above spring, i.e , across 536 coils, should be 



-V 



QAg-^^") 



a/ ? = 0-82 seconds 



V 0018.386-4 



