62 THE POPULAR SCIENCE MONTHLY. 



quirements of the case, and to be a necessary consequence of the best 

 knowledge we can obtain as to the genesis of our system and the con- 

 stitution of the sun itself, it must, of course, be conceded that it does 

 not yet admit of any observational verification. No measurements 

 within our power can test it, so far as appears at present. 



It may be admitted, too, that much can be said in favor of other 

 theories ; such as the one which attributes the solar heat to the im- 

 pact of meteoric matter, and that other most interesting and ingenious 

 theory of the late Sir William Siemens. As regards the former, how- 

 ever, I see no escape from the conclusion, that if it were exclusively 

 true, the earth ought to be receiving, as was pointed out by the late 

 Professor Peirce, as much heat from meteors as from the sun. This 

 would require the fall of a quantity of meteoric matter — more than 

 sixty million times as much as the best estimates make our present 

 supply, and such as could not escape the most casual observation, since 

 it would amount to more than a hundred and fifty * tons a day on 

 every square mile. 



As regards the theory of Siemens, the matter has been, of late, so 

 thoroughly discussed that we probably need spend no time upon it 

 here. To say nothing as to the difficulties connected with the estab- 

 lishment of such a far-reaching vortex as it demands, nor of the fact 

 that the temperature of the sun's surface appears to be -above that of 

 the dissociation-point of carbon compounds, and hence above the 

 highest heat of their combustion, it seems certainly demonstrated 

 that matter of the necessary density could not exist in interplanetary 

 space without seriously affecting the planetary motions by its gravi- 

 tating action as well as by its direct resistance ; nor could the stellar 

 radiations reach us, as they do, through a medium capable of taking 

 up and utilizing the rays of the sun in the way this theory supposes. 



And yet I imagine that there is a very general sympathy with the 

 feeling that led to the proposal of the theory — an uncomfortable dis- 

 satisfaction with received theories, because they admit that the greater 

 part of the sun's radiant energy is, speaking from a scientific point of 

 view, simply wasted. Nothing like a millionth part of the sky, as seen 

 from the sun, is occupied, so far as we can make out, by objects upon 

 which its rays can fall : the rest is vacancy. If the sun sends out rays 

 in all directions alike, not one of them in a million finds a target, or 

 accomplishes any useful work, unless there is in space some medium to 



* In an article on astronomical collisions, published in the " Nor1;h American Review " 

 about a year ago, I wrongly stated the amount at fifty tons. There was some fatality 

 connected with my calculations for that article. I gave the amount of heat due to the 

 five hundred tons of meteoric matter, which is supposed to fall daily on the earth with an 

 average velocity of fifteen miles per second, as fifty-three calories annually per square 

 metre — a quantity two thousand times too great. Probably the error would have been 

 noticed if even the number given had not been so small, compared with the solar heat, 

 as fully to justify my argument, which is only strengthened by the correction. I owe the 

 correction to Professor Le Conte, of California, who called my attention to the errors. 



