28S 



TUB POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



fire, some of the heat produced in the fire does 

 the work of driving the engine along, and some 

 of it is wasted in making the engine hot. If the 

 stoker makes a bigger fire, and drives the engine 

 along faster, there will be more heat used in driv- 

 ing it along, and also more heat wasted, so that 

 the engine will get hotter. But now if he keeps 

 up the same fire and stops the engine, all the 

 heat will be wasted in making it hot, and it will 

 get a very great deal hotter than before. 



When a muscle is lifting a weight, it is really 

 driven by the burning (so to speak) of its sub- 

 stance. Some of the heat so produced is used in 

 contracting the muscle, and some of it is wasted 

 in making it hot. When more work has to be 

 done, more burning goes on, more heat is used 

 in doing the work, and more heat is wasted in 

 making the muscle hot. If, however, we could 

 keep up the same amount of burning when the 

 muscle was not doing any work, all the heat would 

 be wasted in warming it, and it would get very 

 hot indeed. 



A muscle is an imperfect machine because it 

 wastes some of the energy supplied it in convert- 

 ing it into work. But all machines do this. It 

 has the great advantage of always changing the 

 quantity of fuel consumed according to the work 

 it has to do. In this way it is like what a steam- 

 engine would be if the machine which indicates 

 the rate of doing work were connected with the 

 fire-draught, so as to make always more or less 

 fire according as there was more or less work to 

 be done. 



I must apologize for taking up your space 

 with explanations whose proper place is in little 

 simple easy books for schools. My excuse is 

 that some of your readers may not have had the 

 opportunity of learning from these primers, and 

 may not have children at school from whom they 



could get the information. Such readers might 

 be misled by the writer I have quoted from. 



A little prince, I suppose, might grow to be 

 twelve years old, and not be able to understand 

 the two things I have endeavored to explain. He 

 might then have little simple easy books, written 

 by wise men entirely for his own use, that he 

 might learn to understand them and things like 

 them. 



But when a grown-up person not only does 

 not understand these things, but thinks fit to 

 write about them, it is only too probable that he 

 would not understand any better if all the wise 

 men in the world wrote easy little books for him. 



If a man thought Turkey was a part of France, 

 and also that he was fit to lecture Lord Salisbury 

 on foreign affairs, would there be any use in draw- 

 ing maps for him ? 



Such a consideration will perhaps explain why 

 the writer in question, and others like him, do not 

 get replied to by any one who is allowed to em- 

 ploy his time profitably. I am sorry that he 

 should be disappointed in this way, but it can 

 hardly be helped. He evidently hopes that some- 

 body will think it worth while to deny his modest 

 statement that he demolished the doctrine of pro- 

 toplasm. If he said he had swallowed the moon, 

 would he expect the man in the moon to come 

 hurrying down to assure us it was a mistake ? 



W. K. Clifford. 



P. S. — One should be careful not to accept 

 the account of the opinions of others given by 

 writers of this kind, because they cannot copy 

 out rightly what they do not understand. This 

 one does me the honor to say that I spoke of the 

 universe as made of atoms and ether. What I 

 really said was that the physical universe is made 

 of atoms and ether. — Nineteenth Century. 



