OF ARTS AND SCIENCES. 103 



In passing land, loose substances, as the debris of trees and buildings, 

 are raised ; in passing water, vapor and spray are raised, as in the 

 ocean-spouts, by one and the same power. The shape of the lower 

 cone is, however, better defined and more uniform in the water than 

 in the land spout, the supply of materials to form the latter being more 

 variable on land. There is, however, an exception to this, when the 

 land-spout passes over desert sands, which give the appearance of 

 moving pillars of dust extending from the earth to the skies. Bruce, 

 in his travels, describes them as tall pillars, and says he sometimes saw 

 many of them travelling together. 



" The materials raised on the land were precipitated from the cloud 

 before it had passed half way across the water, and on the opposite 

 side it began to raise other movable substances. The water over 

 which it passed was thrown into violent ebullition, like an immense 

 cauldron, giving off a dense vapor and spray from ife surface over an 

 area of three hundred feet in diameter. A flash of light or electricity 

 was seen by two observers darting through the cone, which was fol- 

 lowed by a lessened commotion of the water, and a fall of rain. The 

 track of the tornado was two to three hundred feet wide, deviating little 

 if any from this width for several miles, its limits being strongly 

 marked on the ground and upon trees. Even the same tree, that 

 stood on the margin of the track, had its trunk killed, the sap being 

 dried, as it were, on one side, and not on the other. Peltier describes 

 similar effects from a spout in Fontenay, where ' the side of trees af- 

 fected by the meteor was dried, while the opposite side preserved the 

 sap.' The diameter of the shaft or cone, midway between the cloud 

 and earth, was apparently less than fifty feet. 



" The length of the visible cone that shot down from the cloud va- 

 ried every minute. Sometimes it seemed to elongate in a tapering 

 form quite to the earth, and then to shorten again. This, of course, 

 was an optical illusion, for there is no descent of the spout in such 

 cases, but merely a condensation of vapor, whose particles are con- 

 stantly ascending, whether visible or not. And were the condensation 

 of vapor to descend as far and wide upon the earth as the dynamic 

 effects of the tornado extend, we should see the form of the terrestrial 

 cone shooting upward to meet the descending inverted cone, — they 

 would be continuous from the earth upward ; and this, in fact, is ex- 

 hibited in water-spouts, the water supplying the vapor to make a con- 

 tinuous visible spout, extending from its surface into the cloud, which 

 slightly resembles in form an astral lamp. 



