5o6 THE POPULAR SCIENCE MONTHLY. 



seems to me to be tlie highest field for the exercise of our intel- 

 lectual faculties, for it includes ethics on the one hand and psy- 

 chology on the other, both together constituting the phenomena 

 of mind, while the visible results are conditioned by the attributes 

 of matter. But to-night I propose to begin on a much lower 

 plane, and to attempt only the suggestion of one or two simple 

 laws which are common to nonliving structures, to living beings, 

 and to an organized society. 



Since the metamorphoses of matter are endless in number and 

 infinite in succession, let us limit the word "change" to some 

 fixed and definite alteration, such as the burning of an ounce of 

 gunpowder, the falling of the water of Lake Erie over the cliff at 

 Niagara, or the duration of a human life from infancy to old age. 

 In this restricted sense physicists and chemists have recognized 

 two kinds of changes: first, those which tend to go on indefi- 

 nitely until all the matter present has suffered the alteration in 

 question ; second, those which give rise to products which are un- 

 favorable to the original forces at work such changes are self- 

 limited and may cease, therefore, long before all the material has 

 been used. As an example of the first type that of unlimited 

 change I may again cite Niagara, for here the falling water sets 

 up no reaction against itself. This is the popular idea of a 

 change, because we seem to be surrounded only by such cases. 



The falling snow or rain, the uprooting of trees by a whirl- 

 wind, the constant streaming away of light from a lamp or heat 

 from a stove, with the concomitant burning of fuel, all are famil- 

 iar experiences and they are unlimited in character. But while 

 these and others like them have served to stamp the word 

 " change " with a definite meaning in the mind of the public, it 

 is because they seem the only types to a superficial observation. 

 In reality, however, the other kind, the self-limited changes, are 

 vastly more numerous. Take as an example the freezing of 

 water : the moment ice is formed it acts as a partial nonconductor, 

 or blanket, to keep heat from escaping, and so the rate of freezing 

 is diminished, and here in our climate is wholly stopped when a 

 thickness of two feet of ice is reached. Or, again, consider the 

 case of an elastic body on which a weight is placed. If it is 

 a spring, it will bend, and finally, if the weight is not too great, 

 will reach a position where the latter is just supported. This 

 equilibrium is brought about by the internal stress of resili- 

 ence of the spring acting against the force of gravity, and thus 

 the change in position of the weight -has called forth a power 

 which is the result of that change, and at the same time limits 

 it in amount. 



While this illustration is an elementary one, it is for all that 

 exceedingly important, because it is so common ; it covers every 



