312 THE POPULAR SCIENCE MONTHLY. 



ent altitudes and velocities of air-currents. It ia estimated that in the 

 center of the funnel the air sometimes attains the enormous speed of 

 two thousand miles an hour. The whirling movement is almost inva- 

 riably in an opposite direction from that taken by the hands of a 

 clock. 



The weather-predictions of the Signal Service are distinct from the 

 tornado-predictions, which involve local treatment that severely tests the 

 science of meteorology. It is true the tornado region follows the usual 

 storm-center along parallel lines, but at a distance of several hundred 

 miles. The tornadoes develop far from the storm-center, and generally 

 under conditions of partial sunshine and cloudiness and high humidity 

 or excess of moisture. The relation of tornado-prediction to the usual 

 ■weather-service is only in regard to details of temperature, wind-direc- 

 tion, dew-point, etc., as furnished by the general weather reports. The 

 prediction of the movement of the usual storm-center is by no means so 

 difficult as the attempt to even approximately locate the general region 

 where a series of tornadoes will occur, because of the narrow track in 

 which the destructive power is manifested. The officers of the Signal 

 Service are careful to make no rash promises. While knowledge of the 

 phenomena is not entirely complete, yet the advancement of the science 

 is so marked and positive that tornadoes can be predicted for certain 

 parts of States with a degree of average certainty that will, if carried 

 out by the establishment of a system of signals in 1886, prove of very 

 great value to the people. Already insurance companies have been 

 enabled to take millions of dollars of tornado risks, and the more com- 

 plete knowledge of the average danger for given localities will set the 

 questions of p7-emiums and rates of insurance upon a basis that will 

 be profitable for the people as well as for the companies. The danger 

 in localities will be established by averages, and the amount of pre- 

 caution necessary will be known, and may be expressed in trustworthy 

 percentages. This will economize expenditure both for insurance and 

 tornado-retreats underground. The protection to life will be a very 

 marked feature of the results attained. The approach of the tornado 

 along its almost inevitable path, of from southwest to northeast, can 

 be seen for fully an hour above the surface of a flat prairie, thus 

 enabling people to get far beyond the reach of its narrow but fear- 

 fully destructive path. With this we close the question of the predic- 

 tion of tornadoes for certain parts of States. 



Let us now examine the closer prediction made by the trained 

 observer or tornado-reporter, as he sees the tornado-cloud in process 

 of formation. The question as to whether the furious movement of 

 the clouds is forming the funnel-shape so much dreaded can only be 

 decided by careful study of the sights and sounds described by hun- 

 dreds of observers. A very important characteristic of tornado air- 

 currents is that the disturbance begins in the upper air. In the 

 "North American Review" for September, 1882, Professor T. B. 



