862 Dynamic Theory. 



knew the fact that it did come, and that furnished him a reason for 

 pushing it down. Half the human beings who use pumps, reason no 

 further on the subject than that ; and even when they do, their reason- 

 ing, pushed as far as possible, ends at a barrier where the only solution 

 attainable is, "this thing is so, just because it is. " In other words, 

 my senses tell me it is so, but they do not show any antecedent cause 

 for it. For example, we may trace the origin of energy to the attrac- 

 tion of gravitation, but all we can tell about gravitation is that it exists. 

 We utterly fail to see any cause behind it. The only difference between 

 the reasoning of the horse and that of the man, is that the former 

 sooner reaches the limit beyond which his senses disclose no further re- 

 lationship of cause to the visible effect. His intelligence compared with 

 that of man, is simply as a less quantity compared with a greater. 



It has long been customary to attribute all the actions of the lower 

 animals to instinct. If by instinct we mean a powerful tendency to do 

 a thing according to a hereditary habit in the face of a strong and ob- 

 vious stimulation toward a variation from the habit ; and if by intelli- 

 gence we mean a disposition that allows extraordinary or unusual stim- 

 ulations to modify, influence or control the actions, then we must concede 

 that the actions of all animals, including men, are in part instinctive, 

 and in part intelligent. There are extremely few actions which it is 

 within the bounds of possibility to perform twice exactly alike. Con- 

 sidered in detail, no two bird's nests are precisely alike. The weaving 

 together of the straws, sticks, leaves, feathers, hairs, rags, papers, and 

 what not, that go to compose the nest, is in no two alike ; and they nec- 

 essarily vary in the detail of attachment to the crotch of the tree, or 

 other locality in which they are placed. The general principle of a se- 

 cure receptacle for the eggs, in shape to prevent them rolling out, and 

 in thickness to retain warmth, runs through all, just as a man's house 

 generally includes walls and a roof; but in material and other detail 

 there is great latitude. In some cases, even where long experience and 

 habit have established a uniform method, we find examples of variation 

 when the circumstances appear to demand it, in the case of other ani- 

 mals as well as ourselves. For example, "our common cliff swallow, 

 known also as the cave swallow and the < Republican, ' formerly built 

 against the face of a cliff, and, as a protection against the weather, the 

 nest, instead of being open at the top, was bottle-shaped, the entrance 

 being through a kind of neck at the side. Now that the country has 

 become populous, however, this swallow has taken to nesting under the 

 eaves of barns, where it is shielded from the rain by the overhanging 

 roof. Little by little, therefore, the wise bird has given up its more 

 elaborate method of construction, till now you may see, side by side, 

 nests that are simple mud saucers, nests that are built in the old-fash- 



