KNOWLEDGE BY INVESTIGATION. 255 



2. Their dangerousness or power of inflicting pain. 



3. The best means of effecting a given purpose. 



One of the commonest objects in their experimental in- 

 vestigations is to ascertain the strength of material, in refe- 

 rence especially to its capability to support given body weights 

 or mechanical strains. Thus orangs, before climbing trees, 

 ' test the branches, as to whether they will bear, by shaking 

 them' (Biichner). Cingalese elephants try the strength of 

 bridges before trusting their body weight on them, ' using 

 their foot and trunk, and refusing to venture upon the bridge 

 if vibration is at all perceptible' (Baker, Watson). 



Berkeley tells us of a retriever tiying the strength of ice, 

 and looking for a convenient and safe place to cross a frozen 

 brook. 



Certain animals, again, test the temperature of various 

 fluids or solids. Thus Berkeley reports a male parent bird 

 trying the varying heat of a nest of short-mown grass, which 

 became warm by fermentation. He visits it when full of 

 eggs * very frequently, and tries the temperature with his 

 foot. If too hot, he decreases the grass around the eggs ; if 

 too cold, he heaps on more grass.' Monkeys sometimes try 

 the heat of warm water by the cautious and gradual intro- 

 duction of their feet or fists just as man estimates the 

 temperature of his bath by inserting his fingers or hand. 



Other animals test the quantity of fluid in a given vessel 

 by the use of their paws or feet. The cat, for instance, 

 sometimes gauges or measures the quantity of water, milk, 

 or cream in a jug ascertains the lowness or highness of 

 its level, its accessibility, or the reverse by means of its paw 

 (' Animal World ') ; and the rat probably does the same by 

 the use of its tail. 



Experimental investigation usually or frequently implies 

 both repetition and variation of effort, frequency of attempts to 

 attain a given end, involving diligence, perseverance, deter- 

 mination, with change in the mode or means employed, neces- 

 sitating ingenuity, adaptiveness, reflection, comparison. In- 

 order to success in attaining an object, or accomplishing a 

 purpose, repeated trials may be made of the same kind, as well 

 as of different kinds. Thus birds that break shells on stones 

 18 



