SCIE 



[Entered at the Post-Offlce of New York, N. Y. , as Second-Class Matter.J 



A WEEKLY NEWSPAPER OF ALL THE ARTS AND SCIENCES. 



Eighth Yeae. 

 Vol. XVI. No. 387. 



NEW YORK, July 4, 1890. 



Single Copies, Ten Cents. 

 $3.50 Per Yeah, in Advance. 



THUNDER-STOEMS. 



A TYPICAL thunder-storm is first seen as a dense, ragfged 

 cloud in the west, extending to a height of over a mile. The 

 sty is entirely clear elsewhere, except sometimes covered by 

 a light fleecy veil of cirrus. The cloud in the_ west rapidly 

 enlarges, and completely covers the sky excepi a small por- 

 tion to the east and south-east. The motion of these clouds 

 is distinctly from the west and quite rapid, while the surface 

 wind is from the south and quite gentle. This wind is 

 blowing toward a general storm situated about five hundred 

 miles to the north-west, and has no connection at all with 

 the thunder-storm which is suddenly interjected, as it were, 

 upon the quiet air. Often there are seen two clouds in the 

 south-west and north-west which seem to meet together and 

 produce the storm, but more often the first appearance is 

 that of a great cloud of dust borne upward about three hun- 

 dred feet, and advancing with great rapidity from the west 

 (sometimes eighty miles per hour). Some of the clouds 

 sprinkle a little rain as the dust-cloud advances, but this is 

 very light. When the storm is very severe, a loud roar is 

 heard like the continuous discharge of electricity which pro- 

 duces a steady instead of intermittent thunder. During this 

 time, lightning-flashes are seen and distant thunder heard. 

 In a few moments, after the dust-cloud has approached 

 nearer and practically with it, the wind suddenly whirls to 

 the west, and blows with great velocity (sometimes eighty 

 miles per hour). Then, in a moment or two more, the light- 

 ning and thunder become verj' intense, and rain falls in 

 torrents. Often the lightning's flash is the signal for a 

 fresh downpour, allowing a few seconds for the fall of the 

 rain from its height. This phenomenon has led to the view, 

 now almost universally accepted, that there is a most inti- 

 mate relation of cause and effect in this display of electricity 

 and the subsequent rain. Under some circumstances, but 

 invariably in connection with this heavy rain, there fall 

 hail-stones variously measured from the size of a pea to that 

 of hen's eggs, and even larger. In some cases, larger masses, 

 even as great as an elephant, have been reported, but these 

 are due to a mingling or freezing together of many stones in 

 the air or after they reach the earth. 



Cold Air. 

 During the progress of a thunder-storm, and after its front 

 has reached the observer, there is a remarkable cooling of the 

 air. This cooling seems to arise from a downward current 

 in the centre of the storm. It cannot be due to the onrush 

 of a north-westerly wind, for that must come fi-om a warm 

 region, since the thunder-storm has been suddenly inter- 

 jected into a region of warm southerly winds flowing for hun- 



dreds of miles toward the north. This cooling is often very 

 great, and seems to indicate that the air in the centre of the 

 storm is not abnormally heated, as in the case of a general 

 storm, but is very much cooled. The bearing of this upon 

 the generation of the thunder-storm is of great importance, 

 and does not seem to have been sufficiently considered. 



Environment. 



When the storm passes to the north or south of the ob- 

 server, there is quite a brisk breeze from it, showing that the 

 motion of the air is from it on at least three sides. Often 

 it is possible to view the storm, in its onward progress, with 

 clear sky overhead, if its border does not reach the zenith of 

 the observer. Under these circumstances, one sees very dis- 

 tinctly up to the highest clouds a steady motion to the east. 

 The rain is seen falling in great sheets, and its front is very 

 distinctly marked. This rain front seems to be an important 

 phenomenon, and has been seen scores of times advancing 

 with a slight lagging at the earth and in the clouds. The 

 appearance impresses one at once as caused by a rapid mo- 

 tion in the middle cloud region, with a lagging at the earth 

 possibly from friction, and in the upper part of the cloud 

 from a less velocity at that point. In no instance has there 

 ever been observed an uprush of air anywhere in this region. 

 These storms go in parallel lines; and as many as four have 

 been seen running one behind the other, the most northerly 

 one in advance. Often it is repoi-ted that a storm has gone 

 slightly north of a station, and then turned and come back 

 directly over it ; but this is probably an illusion. The sec- 

 ond storm has a motion the same as the Srst, but goes a lit- 

 tle farther south. The motion across the country of these 

 storms is about double that of the attending general storm 

 to the north-west. 



Probably the most marked characteristic of a thunder- 

 storm, however, is a rise in pressure at its centre. This rise 

 is universally conceded to-day, though its cause is in grave 

 doubt. It has been repeatedly observed in storms where 

 there has been no rain, and hence cannot be due to the cool- 

 ing of the air by the rain, or to its downward pressure as it 

 falls. How is it possible to account for this rise of pressure 

 in a storm which is itself travelling more than a mile a min- 

 ute? We have here to consider a phenomenon entirely dis- 

 tinct from a sand-whirl of the desert, which has only a slight 

 progressive motion. There seems to be no doubt whatever 

 that we are to consider here a cause or a condition which 

 is inherent in the storm itself. There can be no upsetting 

 of the equilibrium, no uprush of air just in front of a thun- 

 der storm and nowhere else, which could give such a rise of 

 pressure in so rapidly a moving body of air. We are cer- , 



