A FALLING STAR. 207 



No doubt there is some heat developed by the combustion 

 of the gunpowder, but the bullet cannot be much warmed 

 thereby ; it is, indeed, protected from the immediate effect 

 of the heat of the powder by the wad. The bullet is 

 partly warmed by the friction of rubbing against the 

 barrel of the rifle, but doubtless it also receives some heat 

 by the friction of the air and some from the consequence 

 of its percussion against the target You need not, then, 

 wonder how it is that when I am checked by your atmo- 

 sphere I, too, am heated. 



" Remember that I move a hundred times as swiftly as 

 your rifle bullet, and that the heat developed in the check- 

 ing of the motion of a body increases enormously when 

 the velocity of the body increases. Your mathematicians 

 can calculate how much. They tell you that the amount 

 of heat potentially contained in a moving body varies 

 as the square of the velocity. To give an illustration 

 of what this means, suppose that two rifles were fired at a 

 target, and that the sizes of the bullets and the ranges 

 were the same, but that the charge in one of the rifles was 

 such that its bullet had twice the initial velocity of the 

 other. Then the mathematician will say that the heat 

 developed during the flight of the rapid bullet might be 

 not alone twice but even four times as great as that de- 

 veloped in the slower bullet. If we could fire two bullets 

 one of which had three times the speed of the other, then, 

 under similar circumstances, the heat generated ere the 

 two bullets were brought to rest would be nine times 

 greater for the more rapidly flying bullet than for the 

 other one. Now you can readily comprehend the im- 

 quantity of heat that will have been produced ere 



