Jan., 1889. 
spencer’s FIRST PRINCIPLES.” 
9 
Were I to criticise Mr. Spencer’s statements point by 
point, there would be danger that we should be confused by 
differences about mere details. I propose therefore to state 
my own beliefs in these matters, and to give as far as I can 
what I consider the warrant for them. 
The main work of the physicist is the investigation of the 
resemblances or similarities which he observes in phenomena. 
The description of these resemblances he embodies in physical 
laws. For instance, he observes that bodies resemble each 
other in falling to the ground when no other body intervenes; 
that they resemble each other in remaining at rest unless 
there is some other body to whose presence their motion can 
be ascribed; that they resemble each other in that they require 
an effort from him to set them moving, an effort which he 
feels through his muscular sense ; and so on. These are mere 
qualitative resemblances which can be discovered by simple 
observation, and every intelligent being has through his own 
observation, through his early instruction and possibly through 
the observation of his ancestors, become aware of & number 
of such resemblances or physical laws which he regards as 
mere common sense. In fact, in this respect, we are all like 
Moliere’s M. Jourdain—we have been speaking physics these 
forty years and never knew it. But the physicist, of course, 
goes far beyond this classification of simple observations. 
He makes experiments as well as observations. He calls in 
the aid of instruments and makes measurements; he discovers 
that phenomena resemble eacli other in various ways which 
can be expressed by numerical relations. Let us take an 
example. 
An experimenter puts a piece of rock salt and a 
vessel of water side by side on the one pan of a balance, and 
counterpoises them by weights on the other pan. He now 
powders the salt and finds the weight is still the same; putting 
the salt into the water and stirring till it is all dissolved, the 
balance is unchanged. Finally, distilling the liquid and 
collecting the water and the salt which remain behind, he has 
them separate, and placing them on the balance, they are 
counterpoised by the same weight as before. This experiment 
may serve as a type of all the various weighing experiments, 
chemical and physical, which are taken as proving the 
indestructibilitv of matter. 
«/ 
What conclusions does our experimenter draw ? Firstly 
that the salt was in existence throughout the experiment, 
and secondly that its weight remained the same. But in 
drawing this conclusion he makes assumptions. He believes 
that the salt appearing after distillation is the identical salt 
