2 SCIENTIFIC APPARATUS. 



tion we regarded as disturbances. The experiments must now be 

 designed so as to bring into prominence the phenomena which we 

 formerly tried to get rid of. When we have in this way ascer- 

 tained the laws of the disturbances, we shall be better prepared 

 to make a more thorough investigation of what we began by 

 regarding as the principal phenomena. 



Thus, in experiments where we endeavour to detect or to 

 measure a force by observing the motion which it produces in a 

 movable body, we regard Friction as a disturbing agent, and we 

 arrange the experiment so that the motion to be observed may be 

 impeded as little as possible by friction. 



2. APPARATUS. 



Everything which is required in order to make an experiment is 

 called Apparatus. 



A piece of apparatus constructed specially for the performance 

 of experiments is called an Instrument. 



Apparatus may be designed to produce and exhibit a particular 

 phenomenon, to eliminate the effects of disturbing agents, to regu- 

 late the physical conditions of the phenomenon, or to measure the 

 magnitude of the phenomenon itself. 



In many experiments, special apparatus is required for all these 

 purposes, but certain pieces of apparatus are used in a great variety 

 of experiments, and there are whole classes of instruments which 

 have certain principles of construction in common. 



Thus, in all instruments in which motion is to be produced 

 there must be a prime mover or driving power, and a train of 

 mechanism to connect the prime mover with the body to be 

 moved; and in many cases additional apparatus is necessary 

 such as a break to destroy the superfluous energy of the prime 

 mover, or a reservoir to store up its energy when not required ; 

 and we may have special apparatus to measure the force trans- 

 mitted, the velocity produced, or the work done, or to regulate 

 them by automatic governors. 



