EFFECTS OF LIGHTNING ON ROCKS AND SOIL. 655 



The curve representing the distribution of heat resembled that obtained 

 from the spectrum of the sun, the invisible calorific radiation being re- 

 duced by the water from nearly eight times to about twice the visible. 

 Could we get above the screen of atmospheric vapor, a large amount 

 of the ultra-red rays would assuredly be restored to the solar spectrum. 

 This conclusion has been recently established on the grandest scale by 

 Professor Langley, who, on the 10th of September, wrote to the lect- 

 urer from an elevation of twelve thousand feet on Mount Whitney, 

 "where the air is perhaps drier than at any other equal altitude ever 

 used for scientific investigation." An extract from Professor Lang- 

 ley's letter will fitly close this summary : " You may," he says, " be 

 interested in knowing that the result indicates a great difference in the 

 distribution of the solar energy here from that to which we are accus- 

 tomed in regions of ordinary humidity, and that, while the evidence of 

 the effect of water-vapor on the more refrangible rays is feeble, there 

 is, on the other hand, a systematic effect, due to its absence, which 

 shows, by contrast, its power on the red and ultra-red in a striking 

 light. These experiments also indicate an enormous extension of the 

 ultra-red spectrum beyond the point to which they have been followed 

 below, and, being made on a scale different from that of the labora- 

 tory on one, indeed, as grand as Nature can furnish and by means 

 wholly independent of those usually applied to the research, must, I 

 think, when published, put an end to any doubt as to the accuracy of 

 the statements so long since made by you, as to the absorbent power 

 of this agent over the greater part of the spectrum, and as to its pre- 

 dominant importance in modifying to us the solar energy." 



--*- 



EFFECTS OF LIGHTNING- ON ROCKS AND SOIL.* 



By STANISLAUS MEUNIER. 



THE effects of lightning on the tops of mountains are often very 

 intense. Among them have been cited such works as the trans- 

 portation of large masses to a considerable distance. They also fre- 

 quently include the development of high degrees of heat. The clearest 

 possible proof of this fact is afforded by the superficial fusion of rocks, 

 even of such refractory ones as granite and other crystalline stones. 

 Laussure long ago described vitrifications of this kind on the summit 

 of Mont Blanc ; Ramond has found them on the Pic-du-Midi, and 

 Humboldt in Mexico ; and the characters they exhibit are every- 

 where uniform. 



The vitrifications are generally only a few tenths of a millimetre 

 thick, but they sometimes extend over surfaces of nearly a square 



* Translated from " La Nature." 



