The Weather Signal System

The bitter woather of tho 13th will not i forgotten. It was especially dis1 'lo as ïollowing upon a euason of thaw that was vvorthy of Jamuiry. Suoh i and radical chungo luis icldom boon oxperiencod. Up to uridnight the moi-eury in the tliormomoterstood atabout forty-thrse dogroes, with a vui-y light movement of tlie atmosphero. Koon aftor midnight a storm set in, tbe icy wind bluw with alrnost lmrrJcane forcc, and tho mereury sunk rapidly. In ten houra tho temperatura had dropped thirtythree degrees, ,i i; grewstill coldor as the day advanoed umi shadud oii' iiito tko night. Tho observations of tho weathor, made at nearly fifty different point8 in the ünii i (■:, by the Signal Service Corps of vhe United States Army, ennble us to se& thtit this Hiidilon ohange in Chicago was but an item in a general atinospheric nent of great extent. Our first promoiiition of tho phenomonon came on Sunday night, in a telegram from Fort Benton. The thermometer at that point feil to zero on Sunday afternoon, about four o'clock, Chicago timo. At about eleven o'elock on that night the temperaturo at Fort Benton feil to 11 degroes below zero, and it was 15 degrees below at six o'clook Monday morning, while none of the other signal stations in tho Northwest exhibitod any marked chango of temperature. But during tho day on Slondaythe mercury feil 35 degrees at Omaha, and some eight to twelre hours later a similar chango oceurred in Chica go. During all this time the temperaturo at stations several hundreds of miles south of Fort Benton, Oiuahu and Chicago, underwent no inarked variation. Theso fact8ghow us fchat our city layin the path of a vast atmospherio wave, which burst upon Chicago from tho northwest, haying traversen the dütanoe of 1 '■■■■ .i bun Li l miles from Fort Benton in two dLiys, or at thö rate of twenty-fivo to thirty miles per hom', llow far west of Fort Benton it originated we cannot now gay, but we havo good reason to believo that Chicago is f ar from the terminus of lts Bweep. The thermometer eonditions, as telgraphed Last evening:, indícate that it has already passed far to the southeast, and that a portion of the wavi-, after ]!ii.-ing down the Valley ot' en deflectsd to ;ho eoutliwaid, and was last night spendug its fury on Western Illinois and Ëaeturn Missouri. Tlie breadth of this volume of moving tir is unknown. It did not ux.tend far to ;he southward of the line running from b'ort B&utoii to Omaha, us is shown by he faot that Virginia City and (heyiiui! were coiuparatively unaÖ'ected by t. But thore cun 1; Bcarceiy a doubt ;hat tho northern range of its oourae erxtrnili (1 ;tt least ono handred miles from :hat line, in which case the wave of in lense oold will have been feit with especial suverity in Northern Dakota and Vlinneaota, and probably ia theLuknSuorior rt'i'tn. It inay bn that Eastern Wiscousin has been visit d but niildly. It is worthy of notice that the mercury n tho barometer stood unusually low at all the stations noted, and rose rapidly with tho advanoe of this wavo of cold. The barometer rose us ths thermometer uli, showing that the frigid visitation waï eitliy due to tho movement of a vast volume of air which increased the total reight of all thu uir above tLo places it assed over. It has lorig been known that these novementa of vast atmospheric waves over large portions of tho earth's surface kre general betweenthe trópica; but the" act that tliey occur equally in the temicrate zones, though not with the same vguiaiify, has only been known within a 'ew yeais. It is yet scarcely sixtoen. Donths since a conneoted series of obsei'vations of the weather at widely sundered places was begun in the United States ;; ut the knowledgo already gained therey is of immonso value. We DoawKnow hat vory few tttmospherio changos of nagnitude occur at any cm: place withjut the ooourrence of similar changos at Other prints far distaiit. And, what is of even greater practical value, it is now uiowh that theso ohanges do not occur imultaneously. They travel, so to speak, 'rom one point to another, with a detinite rate of speed, which very seldoia exceeds 'orty five miles per hour, so that it ispossible to tellgraph the tact of the ap- ronch of a storm of wind, or of heat and iold, long beforoits arrival. In this way the advent of several storms on tho lakes ïas been predicted within tho past year, ong cnongh in advanco to enablo those n charge of vesóels to prepare fer the evont. The systf.'m of storm telegraphy now in uso in the United States is far from béng perfect, but tho resulte attained are very gratifying, and the progress alrealy achievod towaid weather wisdom lias een so rapid that we may reasonably I thoso prognoses to be all but iuallible at no distan t day.