290 FROM NEBULA TO NEBULA 



and makes for the permanency of the physical universe 

 as we now behold it. Collisions and impacts, on the con- 

 trary, breathe of the accidental, the transitory, the in- 

 sufficient. The tacks that draftsmen use may easily be 

 driven into the board by merely pressing the thumb upon 

 them, but they can just as well be driven in with blows of 

 a hammer. Once driven home, you may either continue 

 the pressing or the pounding, but the tack goes, and can 

 go, no farther. Science says this surplus pressure is not 

 conserved, but that the excess blows are. I take issue 

 with this narrow interpretation and submit the following 

 reasons for your consideration: 



The force of a hammer blow may be ascertained in 

 terms of dead weight by merely letting fall on the pan of 

 a spring scale and noting the poundage it registers. With 

 such blows as this you may drive in a stake, or beat an 

 anvil, or do many other things you might have in mind to 

 do. If you cared to, you would not need to drive in the 

 stake with the hammer at all, but you could hunt up a 

 boulder exactly the weight of the hammer-blow as indi- 

 cated on the scale, and this boulder, if merely rested on 

 the top of the stake ought to press it into the ground 

 quite as surely. If instead of driving in the stake, you 

 chose to beat the anvil, you will not displace the latter, 

 but you will heat it. Now, if you please, put the hammer 

 aside and bring the boulder and lay it on the anvil and 

 you will find that the boulder will warm the anvil as much 

 as did the hammer-blows and continuously. And why 

 should this not be so? For how, I pray, is the anvil go- 

 ing to distinguish between a rapid succession of such 

 blows, divided by no interval, and absolute continuity of 

 the bearing weight? It is no more necessary for gravi- 

 tation to go the roundabout way of first causing a fall in 

 order to bring about the impact as a means of producing 

 heat than it was for Charles Lamb's Chinese to fashion 

 the fagots into a hut before starting the blaze for the 

 roasting of the pig. 



It is a customary thing in arguing for the doctrine of 

 the conservation of energy to cite the illustration of rais- 



