496 



SCIENCE. 



[N. S. Vol. XIV. No. 352. 



for $5 to members or others who subscribe for 

 it before its issue. 



2. ' The Evolution of Mine-Surveying Instru- 

 ments.' This will be a volume of about 400 

 pages, issued in the same style as the foregoing, 

 and containing the original paper of Mr. Dun- 

 bar D. Scott on that subject {Transactions ^ 

 XXVIII.), first published in 1898, together with 

 later papers continuing the same subject, and 

 discussions thereof, by Hoskold, Lyman, Davis 

 and many others. Subscriptions will be re- 

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DISCUSSION AND CORRESPONDENCE. 

 WEATHER CONTROL. 



A CHARACTERISTIC of storms which meteor- 

 ologists do not perhaps sufficiently consider is 

 that they are the falling down or collapsing of 

 unstable states of the atmosphere. Such phe- 

 nomena in thermodynamics are called reversi- 

 ble processes ; let us call them sweeping processes 

 or simply sweeps. The trend of a sweeping 

 process may be affected to any extent, however 

 great, by a cause, however insignificant, pro- 

 vided the cause acts at the critical initial stage 

 of the sweep. For example, a mere breath may 

 determine whether a brick chimney shall fall 

 harmlessly into a vacant lot or with unmeas- 

 ured calamity into an adjacent factory, or, to 

 take an example from meteorology, an unstable 

 state of the atmosphere over the United States 

 may lead to a cyclonic movement the effects of 

 which may differ enormously according to the 

 time and place that the unstable state begins 

 to break, and in the limiting case the flight of 

 a grasshopper in Colorado or Montana may be 

 the determining factor. 



If the cyclonic movements of the atmosphere 

 which have so much to do with the distribu- 

 tion of rainfall are ever to be controlled by the 

 infinitesimal means at the disposal of man it 

 must be by the proper application of these 

 means during the early and exceedingly sensi- 

 tive stages of these vast sweeping processes. 

 How, when and where to apply our puny 

 power is a matter of detail, of experiment and 

 study. 



We must study the initial phases of cyclonic 



movements in their relations to subsequent trend 

 and character, and we must devise means for 

 inaugurating these initial phases in a way which 

 will lead to desired results. This study has 

 been pursued by the scientists of the Weather 

 Bureau for many years and is the basis of the 

 weather forecasts issued daily by this great 

 scientific department of the government. As to 

 the means for inaugurating at will the storm 

 movements of the atmosphere the smoke-ring 

 cannon of Burgomaster Stiger is the most ra- 

 tional that has yet been suggested, as will be 

 explained later. 



Weather control is, however, not so simple a 

 matter as would appear from the above state- 

 ment. It is a well-known fact that two cyclonic 

 movements initially alike may have very great 

 differences of trend and character. The expla- 

 nation of this fact will be made clear by con- 

 sidering a simple mechanical analogy. Imag- 

 ine a great number of dominoes to be stood on 

 end not in a simple row but in a very compli- 

 cated network of rows and imagine slight dis- 

 turbances to be produced over the entire sys- 

 tem ; for example, a number of grasshoppers 

 might be turned loose into the dominoe en- 

 closure ! Now there might be one particular 

 region where the dominoes are more sensitive 

 than elsewhere so that collapse would usually 

 start in this region and spread over the system, 

 but the ultimate trend and character of the 

 collapse would depend not only upon its initial 

 phases but quite as much upon whether a par- 

 ticularly vigorous grasshopper had happened 

 to kick over a dominoe or two in regions re- 

 mote from the starting point of the main col- 

 lapse. The driving energy of the dominoe 

 storm at any given place is derived from the fall- 

 ing of the dominoes at that place and not at all 

 from the remote source of the storm, and if we 

 could imagine the spreading dominoe storm to 

 gradually make the dominoes just ahead of it 

 taller and taller then there would be local dis- 

 plays of excessive violence as these tall domi- 

 noes fall. It is scarcely necessary to alter the 

 wording of the above statement, so evident is 

 its application to a vast stretch of atmosphere 

 over a sun-heated continent. The dry arid 

 regions where the sun beats down without hin- 

 drance are the regions in which the atmosphere 



