THUNDER-STORMS. 



52' 



speric air, there are various foreign substances occasionally suspended in it, of 

 which the chief but not the only one is the vapor of water. Carbonic acid ex- 

 ists in it in variable quantity but it is nowhere totally absent. SAUSSURE 

 found it in air collected at the top of Mont Blanc. FUSINIERI states That he 

 constantly found sulphur, iron, and its different oxides, in fissures through 

 which lightning has forced its way. 



If such analogies be considered to have any weight, it is not impossible to 

 imagine the constituents of solids to be suspended in the atmosphere in a 

 vaporous sublimated state, and to coalesce and enter into combination by the 

 transmission through them by a strong discharge of electricity. But as a* mat- 

 ter of fact is it proved that ponderable masses in a state of ignition have actu- 

 ally fallen from the clouds ? The following evidence is produced by M. Arago 

 on this question : 



Boyle states that in July, 1681, the British ship Albemarle was struck with \ 

 lightning off' Cape Cod. A mass of burning bituminous matter fell in tho boat 

 suspended at the stern of the vessel, which diffused an odor like that of gun- 

 powder. It was consumed in the place where it fell, after ineffectual ef- 

 forts to extinguish it by water, or to throw it out of the boat with rods of 

 wood. 



Silent lightnings, whether they appear in a clear or clouded sky, are usually 

 explained by the supposition that they are the reflection of lightnings which 

 issue from clouds below the horizon, and so distant that the thunder which 

 accompanies them cannot be heard. It has been, on the other hand, objected, 

 that the splendor of lightning is not sufficiently intense to cause a reflection so \ 

 bright as the silent lightnings, and that a reflection inferior in brightness to light- 

 ning itself in the same proportion as twilight is to the brightness of the sun, 

 would not be visible. To this objection M. Arago replies by the following 

 facts : 



CASSINI and LACAILLE, when engaged in making a series of experiments on 

 the velocity of sound, in the year 1739, saw the light produced by the dis- 

 charge of a piece of ordnance placed at the base of the lighthouse of Cctle, 

 although at the station they occupied both the town and the lighthouse were 

 concealed by intervening hills. 



la 1803 M. ZACH gave signals on the Brockcn (a mountain of the Harz 

 range), by exploding six or seven ounces of gunpowder. The light produced 

 by this was seen by observers stationed on Mount Kellenberg, at a distance of 

 nearly three leagues from the Brocken. Since a direct view would have been 

 rendered impossible by the convexity of the earth, the light must have been seen 

 by reflection. 



The flashes of artillery discharged at the base of the Hold dts Invalided, at 

 Paris, are visible in the gardens of the Luxembourg, near the Rue d'Enfer, 

 although the highest point of the dome of the hotel is invisible from that place. 



If, then, the feeble effect produced by the explosion of a few ounces of gun- 

 powder be sufficient to be so apparent by reflection, may it not be expected 

 that the more resplendent illumination produced by lightning would be infi- 

 nitely more vivid ? 



That this mode of explaining silent lightning may not take the character of 

 mere conjecture, it will be necessary to show that distant lightnings are actually 

 visible when the thunder which accompanies them is inaudible. Two unex- 

 ceptionable observations are adduced for this purpose. 



On the night between the 10th and llth of July, 1783, the weather being 

 calm and the sky unclouded, Saussure, stationed at theHospice of the Grimsel, 

 looking in the direction of Geneva, saw on the horizon some streaks of clouds 

 from which lightning issued, but no thunder was heard. It was afterward as- 



