342 FKAGMENTS OF SCIENCE. 



During the day the grass, and the earth beneath it, 

 possess a certain amount of warmth imparted by the 

 sun ; during a serene night, heat is radiated from the 

 surface of the grass into space, and to supply the loss, 

 there is a flow of heat from the earth to the blade. 

 Thus the blade loses heat by radiation, and gains heat 

 by conduction. Now, in the case before us, the power 

 of radiation is great, whereas the power of conduction 

 is small ; the consequence is that the blade loses more 

 than it gains, and hence becomes more and more 

 refrigerated. The light vapour floating around the 

 surface so cooled is condensed upon it, and there accu- 

 mulates to form the little pearly globe which we call a 

 dew-drop. 



Thus the boy finds the simple and homely fact 

 which addressed his senses to be the outcome and flower 

 of the deepest laws. The fact becomes, in a measure, 

 sanctified as an object of thought, and invested for him 

 with a beauty for evermore. He thus learns that 

 things which, at first sight, seem to stand isolated and 

 without apparent brotherhood in Nature are organically 

 united, and finds the detection of such analogies a source 

 of perpetual delight. To enlist pleasure on the side of 

 intellectual performance is a point of the utmost im- 

 portance ; for the exercise of the mind, like that of the 

 body, depends for its value upon the spirit in which it 

 is accomplished. Every physician knows that some- 

 thing more than mere mechanical motion is compre- 

 hended under the idea of healthful exercise that, 

 indeed, being most healthful which makes us forget all 

 ulterior ends in the mere enjoyment of it. What, for 

 example, could be substituted for the action of the 

 playground, where the boy plays for the mere love of 

 playing, and without reference to physiological laws ; 

 while kindly Nature accomplishes her ends uncon- 



