Tornadoes

To the elabórate researchea of Mr. Rodfield, of New York, who published, in 1831, the first of a serios of remarkable papers on the phenomena of storms, we owe our first full acqtiaintance witli the origin and progresa of these tornadoes or liurricanes of whieh we have had sucb. an abundance this summer. Mr. Redfield's initial proposition that the hurricane is a progressive vortical whirlwind has been fully sustained, as also his auxiliaiy proposition that the progresa of the vortex is in the line of a parábola, with the curve making awny iïorn the - a consequence, it is believed, of the revolution of the earth Upon its axis. But while these are " fixed f acts," concerning the origin and cause compuratively little is positively known. It used to be cominon to attribute them to more occult forcea, such as electriuity, but the immense mechanical power stored up in the heat and vapor of moist air, as abundantly demonstrated by Espy, Pealin and Reye, is now believed suflicient to account for all tlie wonderful exhibitions of force iu the gyratory hurricane. Vhenever a lower stratum of warm, moist air is rapidly elevated above the sea level, which may bo by various causes, there at once oceurs an influx of air from all sides, and the formation of the whirl commenoes. lts subsequeut development depends upon the supply of moist air, and the sizo of the original vacuüm, and, once fairly whirling, it sets out upon its triumphal parabolic (and diabolic) tour. The velocity of the wind (which must not be coni'ounded with tlie progresa of tlie storm) m these lmrncanes is very difficult to get at. Mr. Redfield exIjiLiílis that over and above the average velocity of tlie wind, come occasional gusts of extraordinary speed and power. It is tliese gusts wliicli do the mischief, and their velocity lias rarely, if ever, been actually gauged. A velocity of 600 miles per hour has been estimated for some of thern, though they should be estimated by the second rather than the íour, for tli e spasmodic increase in the rapidity of the whirl is of very brief lurotion. The velocity of one of these gusts Ín a British lmrncane was flgured at 130 miles the hour, and our own signal corps have record ed as high a speed as ninety miles, without claiming ;o liave measureü the liereer whirls. Tliey are at least fast eiiough for oí) jractical purposes when they break jreat trees like pipe-stems, and set íouses, cattle and men flying over the country.