IN THE LAST HALF-CENTUEY. 109 



a proverbial expression for an instantane- 

 ous action ; but, by the help of the revolv- 

 ing cylinder and the electrical marking- 

 apparatus, it is possible to obtain a graphic 

 record of such an action, in which, if it 

 endures a second, that second shall be 

 subdivided into a hundred, or a thousand, 

 equal parts, and the state of the action at 

 each hundredth, or thousandth, of a sec- 

 ond exhibited. In fact, these instruments 

 may be said to be time-microscopes. Such 

 appliances have not only effected a revo- 

 lution in physiology, by the power of 

 analysing the phenomena of muscular and 

 nervous activity which they have con- 

 ferred, but they have furnished new 

 methods of measuring the rate of move- 

 ment of projectiles to the artillerist. 

 Again, the microphone, which renders the 

 minutest movements audible, and which 

 enables a listener to hear the footfall of a 

 tiy, has equipped the sense of hearing 

 with the means of entering almost as deep- 



