236 THE POPULAR SCIENCE MONTHLY. 



sion that the carbonic acid must have been derived from an external 

 source. 



It appears to me that the theory here advocated furnishes a feasible 

 solution of this geological difficulty. Our earth being situated in the 

 outflowing current of the solar products of combustion, or, as it were, 

 in the solar chimney, would be fed from day to day with its quota of 

 carbonic acid, of which our local atmosphere would assimilate as much 

 as would be necessary to maintain it in a carbonic-acid vapor density 

 balancing that of the solar current ; we should thus receive our daily 

 supply of this important constituent (with the regularity of fresh rolls 

 for breakfast), which, according to an investigation by M. Reiset, 

 communicated to the French Academy of Sciences by M. Dumas on 

 the 6th of March last, amounts to the constant factor of one ten- 

 thousandth part of our atmosphere. The aqueous vapor in the air 

 would be similarly maintained as to its density, and its influx to, or 

 reflux from, our atmosphere would be determined by the surface tem- 

 perature of our earth. 



It is also important to show how the phenomena of comets could 

 be harmonized with the views here advocated, and I venture to hope 

 that these occasional visitors will serve to furnish us with positive evi- 

 dence in my favor. Astronomical physicists tell us that the nucleus 

 of a comet consists of an aggregation of stones similar to meteorites. 

 Adopting this view, and assuming that the stones have absorbed in 

 stellar space gases to the amount of six times their volume, taken at 

 atmospheric pressure, what, it may be asked, will be the effect of such 

 a divided mass advancing toward the sun at a velocity reaching in 

 perihelion the prodigious rate of 366 miles per second (as observed 

 in the comet of 1845), being twenty-three times our orbital rate of 

 motion ? It appears evident that the entry of such a mass into a com- 

 paratively dense atmosphere must be accompanied by a rise of tem- 

 perature by frictional resistance, aided by attractive condensation. 

 At a certain point the increase of temperature must cause ignition, 

 and the heat thus produced must drive out the occluded gases, which 

 in an atmosphere 3,000 times less dense than that of our earth would 

 produce 6x3,000 = 18,000 times the volume of the stones themselves. 

 These gases would issue forth in all directions, but would remain un- 

 observed except in that of motion, in which they would meet the 

 interplanetary atmosphere with the compound velocity, and form a 

 zone of intense combustion, such as Dr. Huggins has lately observed 

 to surround the one side of the nucleus, evidently the side of forward 

 motion. The nucleus would thus emit original light, whereas the tail 

 may be supposed to consist of stellar dust rendered luminous by reflex 

 action produced by the light of the sun and comet combined, as fore- 

 shadowed already by Tyndall, Tait, and others, starting each from 

 different assumptions. 



Although I can not pretend to an intimate acquaintance with the 



