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' (Buchner). Cingalese elephants try the strength of 

 bridges before trusting their body weight 011 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 trying 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 c 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 



