6 On Force. 



quality is proved to be possessed by Matter and by Energy. 

 One of the premises from wliicb he is led to his conclusions 

 is that Matter and Energy are unalterable in quantity, while 

 Force is not so. True enough ; but consider the other pre- 

 mise — that those qualities or entities whose total quantity 

 is unalterable, and those only, do really exist. 



By anything having real objective existence, Professor 

 Tait explains that he means that it exists altogether inde- 

 pendently of the senses and brain processes, by which we 

 are informed of its presence. Whether anything does exist 

 in this independence, I do not know ; nor do I believe that 

 any one else does or can. But without going into the con- 

 troversy between Realism and Idealism, I simply ask whence 

 does Professor Tait obtain his axiom connecting absolute 

 reality and indestructibility ? What higher claim has it to 

 credence than any of the axioms criticised by Mill, in his 

 chapter on Fallacies of Simple Inspection, such as " Circular 

 motion is the most perfect," "Things which we cannot think 

 of together cannot coexist," " Things which we cannot help 

 thinking of together must coexist," "Whatever can be 

 thought of apart exists apart," and so on ? 



Moreover, if the negative portion of the axiom be accepted, 

 although Matter — that is Mass — is proved to exist, Time, 

 Distance, Motion, are degraded to the rank of nonentities 

 along with Force. 



But how is the mass of a body defined and measured ? 

 By the effect which a certain force acting on the body for a 

 certain tirae would produce. And how is energy defined and 

 measured ? As power of doing work — that is, of overcoming 

 a given force through a certain distance. Surely I cannot 

 be accused of presumption in criticising the conclusions of a 

 thinker of Professor Tait's high standard when he tells us 

 that that which is defined in terms of, and measured by 

 means of, that which does not exists has itself independent 

 real existence. 



As probably most of you have read the lecture referred to, 

 it is unnecessary for me to say anything about the most 

 valuable part of it — Professor Tait's exposition of the loose 

 and ambiguous way in which the term Force is often used 

 even by those who should know better. For this he should 

 have earned the gratitude of all lovers of that accuracy in 

 scientific language without which accuracy of thought is 

 almost unattainablCo 



