458 METEOROLOGY. 



site to us it did not appear as dark as when it was approacliiug us, 

 which would indicate that it was not of equal dimensions, but of greater 

 width in the line of its motion. 



The movement of the tornado across the valley was exceedingly 

 rapid; it did not occupy certainly thirty minutes in traversing a line 

 nearly straight of about fifteen miles in length. Tlie ridge of the mount- 

 ain on the side of which we stood was not above GOO feet above the 

 bottom of the valley, and the storm-cloud did not appear more than 

 double that height above us. During the passage of the tornado our 

 ears were constantly impressed with a heavy roaring sound, like that 

 of the Falls of Niagara, in unison with which jieals of thunder in 

 rapid snccession were mingling. The cloud appeared to be generated 

 in place as the tornado advanced; indeed, it might be likened to 

 an immense locomotive-engine passing rapidly over the valley, belching 

 forth smoke and steam. After the tornado had disappeared over the 

 opposite ridge, the whole valley was left covered with a cloud, from 

 which rain continued to fall during the night. 



The path of the tornado was marked on the ground of the bottom of 

 the valley by prostrate trees and other evidences of violent action. It 

 was variable in wultli, being from 100 to 150 yards across. The trees 

 were mostly thrown down on each side of the axis of the path, a 

 larger number on the north side than on the south, about, perhaps, in 

 the ratio of three to one. The path was generally straight and^t)f uni- 

 form widtli, with occasional short bends, as if the tornado had in some 

 places made a sudden lateral movement. Although the princi[)}i] vio- 

 lence of the meteor was confined to the breadth mentiojuMl, yet on each 

 side, for a quarter of a mile, trees were thrown down in the direction in 

 which the storm was advancing. The effects on the northern side or 

 sloi)e, where the tornado entered the valley, were scarcely perceptible, 

 while on the southern slope, or where it left the valley, tliey were very 

 marked. On the northern side it appeared to leap down from above to 

 the bottom of the valley immediately below ; at this point its first 

 prominent mark was made upon a mill-pond, which it entirely emptied 

 of water, sweeping it completely out, and even throwing up from the 

 bottom sticks and stones which had long been sunk in the nmd. The 

 most striking effects were, however, those produced in the lowest parts 

 of the valley, some traces of which could be seen several years after- 

 ward. Its fury was not spent in Spruce Valley, but it left traces of its 

 power for at least twenty miles on the other side of the ridge, in the 

 adjacent valley. 



liEMARKS. — The account of this tornado, which was observed from a 

 very uiuisually favorable position, is very instructive in regard to the 

 cause of the phenonu^non. The two causes to which these remarkable 

 couuuotions of the atmosphere have been referred, are electricity and a 

 disturbance of the pneumatic equilibrium of the atmosphere due to an 

 abnormal condition in regard to temperature and moisture. It is true 



