Prof. Helmholtz on the Interaction of Natural Forces. 507 



the earth, after having been thus brought to rest, should fall 

 into the sun, which of course would be the case, the quantity of 

 heat developed by the shock would be 400 times greater. 



Even now from time to time such a process is repeated on a 

 small scale. There can hardly be a doubt that meteors, fireballs, 

 and meteoric stones are masses which belong to the universe, 

 and before coming into the domain of our earth, moved like the 

 planets round the sun. Only when they enter our atmosphere 

 do they become visible and fall sometimes to the earth. In 

 order to explain the emission of light by these bodies, and the 

 fact that for some time after their descent they are very hot, the 

 friction was long ago thought of which they experience in pass- 

 ing through the air. We can now calculate that a velocity of 

 3000 feet a second, supposing the whole of the friction to be ex- 

 pended in heating the solid mass, would raise a piece of meteoric 

 iron 1000' C. in temperature, or, in other words, to a vivid red 

 heat. Now the average velocity of the meteors seems to be thirty 

 or forty times the above amount. To compensate this, however, 

 the greater portion of the heat is doubtless carried away by the 

 condensed mass of air which the meteor drives before it. It is 

 known that bright meteors generally leave a luminous trail be- 

 hind them, which probably consists of severed portions of the 

 red-hot surfaces. Meteoric masses which fall to the earth often 

 burst with a violent explosion, which may be regarded as a re- 

 sult of the quick heating. The newly-fallen pieces have been 

 for the most part found hot, but not red-hot, which is easily 

 explainable by the circumstance, that during the short time occu- 

 pied by the meteor in passing through the atmosphere, only a 

 thin supei-ficial layer is heated to redness, while but a small 

 quantity of heat has been able to penetrate to the interior of the 

 mass. For this reason the red heat can speedily disappear. 



Thus has the falling of the meteoric stone, the minute rem- 

 nant of processes which seem to have played an important part 

 iu the formation of the heavenly bodies, conducted us to the 

 present time, where we pass from the darkness of hypothetical 

 views to the brightness of knowledge. In what we have said, 

 however, all that is hypothetical is the assumption of Kant and 

 Laplace, that the masses of our system were once distributed as 

 nebulse in space. 



On account of the rarity of the case, we will still further re- 

 mark in what close coincidence the results of science here stand 

 with the earlier legends of the human family, and the fore- 

 bodings of poetic fancy. The cosmogony of ancient nations 

 generally commences with chaos and darkness. 



Neither is the Mosaic tradition very divergent, particularly 

 when we remember that that which Moses names heaven, is dif- 



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