186 Pedler and Cromble — On the Tornado which [No. 2, 



India, averaging perhaps 8 to 10 miles an hour, and they rarely travel 

 faster than about 15 miles an hour, so that consequently a place visited by 

 a cyclone remains under its influence usually for some hours ; 'and, finally, 

 the whole track of a cyclone may be many hundreds of miles in length. 

 Tornadoes or whirlwinds, which, perhaps, from their destructive energy, 

 are alone likely to be confounded with cyclones, are of very different 

 nature. It is true, cyclones and tornadoes are both circular storms, and, 

 in the Northern hemisphere, the rotation of the winds round the centre 

 of these storms is against the hands of a watch ; and in this point they 

 agree, but they differ in many others. As the result of the examination 

 of the character of 600 tornadoes in the United States,* their average 

 size is found to be about 360 yards, the velocity of their progression 

 about 30 miles an hour, the average time consumed by the tornado 

 cloud in passing a given point aboat six minutes, and the average 

 length of the storm track about 28 miles. Another point in which 

 tornadoes differ completely from cyclones is that tornadoes have a 

 distinct diurnal periodicity, usually occurring from 4 to 6 p. m., and 

 they may occur at any season of the year, while fierce cyclones in the 

 Bay of Bengal are confined to limited periods of the year, and they can 

 have, from the nature of the case, no diurnal periodicity at all. It might, 

 however, be objected that perhaps a tornado might grow to a cyclone, 

 but up to the present time such an action has never been known to 

 occur, and thus it must be admitted that there is a sharp line of 

 demarcation between the two classes of storms. 



A tornado, briefly described, is merely a whirlwind of excessive 

 violence, and the tornado cloud usually takes the shape of a funnel, 

 though such descriptions as " cone-shaped," " inverted funnel-shaped, " 

 *' hour-glass-shaped," &c., sometimes occur. The tornado cloud has 

 generally four movements (1) a motion of translation which is in most 

 cases from the south-west to the north-east at perhaps an average rate 

 of 28 miles an hour, (2) a violent rotating motion, the winds moving 

 against the hands of a watch, (3) a swinging to and fro, so that the path 

 of the storm frequently becomes very irregular, and sometimes (4) a 

 rising and falling motion. With reference to the last movement, torna- 

 does have been seen by observers to travel actually for some distance 

 through the air with the lower point of the tornado cloud at a consider- 

 able distance from the ground and simply to strike the ground from 

 point to point. 



The destructive effects of the tornado seem to be vastly more 

 violent than those of cyclones, and the area of destruction is most sharp- 



* Finley, Professional Papers of U. S. Signal Service, Series No. VII., Washing- 

 ton. 



