290 FBAGMENTS 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 re- 

 frigerated. The light vapour floating around the sur- 

 face so cooled is condensed upon it, and there accumu- 

 lates 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 organic- 

 ally 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 importance; 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 something more than mere mechanical motion is 

 comprehended 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 un- 



