64 THE REASON WHY. 



" Cast thy burden upon the Lord, and he shall sustain thee; he shall never 

 suffer the righteous to be moved." PSALM LT. 



Because a portion of the caloriu has left the iron, the particles of 

 which have drawn closer together, and contracted the mass. 



This effect is frequently observed by females in domestic life, who, when 

 they are ironing, or using the Italian irons, find that the heated metal has been 

 too much expanded to enter the box or tube. They find it necessary to wait 

 until the cooling of the iron has had the effect of reducing its dimensions. The 

 expansion of bodies by heat is one of the grandest and most important laws of 

 nature. We are indebted to it for some of the most beautiful, as well as the 

 most awful, phenomena. And science has gained some of its mightiest conquests 

 through its aid. Yet frequently, though quite unthought of, in the hands of 

 the humble laundress, will be found a most striking illustration of this wonderful 

 force of caloric. 



337. Are there any instances in which, the abstraction of 

 latent heat will reduce the bulk of bodies ? 



Yes, there are several. But the most familiar one is that which 

 is exhibited by mixing a pint of the oil of vitriol with a pint of 

 water. A considerable amount of heat will be evolved ; and it 

 will be found that the two pints of fluid will not afterwards 

 fill a quart measure. 



338. Is there any latent heat in air? 



Yes : a considerable amount. In a pint measure of air, though 

 in no way evident to our perceptions, there lurks sufficient caloric 

 to raise a piece of metal several inches square to glowing redness. 



339. How do we know that caloric exists in the air ? 



It has been positively demonstrated by the invention of a small 

 condensing syringe, by which, through the rapid compression of a 

 small volume of air, a spark is emitted which ignites a piece of 

 prepared tinder. 



340. What is the cause of the spark when a horse's shoe 

 strikes against a stone ? 



The latent heat of the iron or the stone is set free by the violent 

 percussion. The same effect takes place when flint strikes against 

 steel, as in the old method of obtaining a light with the aid of the 

 tinder-box. 



What an eloquent lecture might be delivered upon the old-fashioned tinder- 

 box, illustrated by the one experiment of " striking a light." In that box lie, 

 cold and motionless, the Flint and Steel, rude in form and crude in substance. 

 And yet, within the breast of each, there lies a spark of that grand element 



