3o8 THE POPULAR SCIENCE MONTHLY. 



center, a hurricane of more limited extent, and a tornado witli a path 

 only one thousand feet in width — all these must be properly classified 

 before any system for the prediction of tornadoes could reach even 

 approximately verified results. The number of tornadoes occurring in 

 the region east of the Rocky Mountains was one hundred and seventy- 

 two in 1884. The average is more than a hundred yearly. Whenever 

 a tornado occurred, blanks specifying the questions to be asked and 

 the method of investigation to be followed were at once sent to the 

 postmaster or to the principal city or town officers in the vicinity of 

 the scene of destruction, asking for facts, and requesting that the ob- 

 server would kindly volunteer to continue a series of easy meteoro- 

 logical observations for the Signal Service, involving no more outlay of 

 time than the reporter could conveniently spare. The result of this 

 clever device was that the Signal-Office now has upon its books the 

 addresses of more than fifteen hundred reporters in all parts of the 

 country east of the Rocky Mountains, and especially in those States 

 most frequently stricken with destructive tornadoes. Having thus 

 organized a system whereby something like verification of tornado- 

 predictions could be attained. Lieutenant Finley then divided the ter- 

 ritory east of the Rocky Mountains into eighteen districts. He at 

 once began making predictions in these districts, thus reaching a series 

 of recoi'ded averages whereby the results became more definite and 

 local until the close of 1884 and the summer of 1885. The predictions 

 in the latter year have become so effective that during the summer of 

 1886 it is hoped that, by means of signals, hundreds of lives and much 

 valuable property will be saved. 



The most striking examples of the knowledge attained regarding 

 tornadoes are found by reference to the following statistics : During 

 1884, 3,228 predictions unfavorable to tornadoes were made, and of 

 these, 3,201 were verified by reports sent in by tornado-reporters, who 

 are instructed to carefully scan the newspapers as well as note the 

 meteorological phenomena in a given neighborhood. When the con- 

 ditions are unfavorable for the development of tornadoes, there are no 

 unusual contrasts of temperature, the areas of warm and cold air are 

 neither great nor well defined northward and southward, the winds are 

 variable and not very strong, and the distribution of pressure is about 

 normal. 



When we consider that more than a hundred tornadoes occur an- 

 nually, it follows that the successful prediction of safety for eighteen 

 districts is a very satisfactory indication of the advance made by this 

 science. The result is certainly practical and valuable, as with proper 

 signals shown at telegraph-stations the inhabitants of Kansas, Missouri, 

 and other States, can go to their work free from anxiety and not sub- 

 ject to false alarms on the appearance of every harmless thunder-storm. 

 The predictions of safety are therefore particularly valuable in States 

 in which tornadoes are frequent. When, however, wc examine the 



