310 THE POPULAR SCIENCE MONTHLY. 



and the pressiire ranging from 29*90 to 29"70 inches. It has long been 

 known that such a "barometric trough," or stationary depression, 

 forms over the northwestern portion of this continent every summer, 

 when the soil is highly heated by the sun, and the air-strata above it 

 become highly rarefied by terrestrial radiation ; Mr. Buchan, on his 

 isobaric charts, assigns to it in July a mean pressure of 29*80 to 29"70 

 inches. Now, by " the law of the winds," the effect of this baromet- 

 ric depression would be to set up an indraught, somewhat resembling 

 that caused by an ordinary cyclone, around whose center, in our hemi- 

 sphere, the air draws from right to left, and moves on all sides toward 

 the vacuum. Necessarily, therefore, toward the central belt of this vast 

 continental depression (which during last August covered the interior 

 of our continent up to the Arctic Circle), as into an aerial hollow, the air 

 would flow from the surrounding regions of high pressure, which in 

 that month always lie to the southward in the Gulf of Mexico, and in 

 the extratropical parts of the Pacific. Could the Signal-Service baro- 

 metric observations have been supplemented in August by like simulta- 

 neous observations taken in central British America, so as to determine 

 the extent and intensity of the low pressure there, the anomalous au- 

 tumn of 1879 could have been in no small measure foreseen and f orean- 

 nounced. A " warm wave " was then rolling northward and likely to 

 continue. Could the international system of reports have been ex- 

 tended to the upper valley of the Saskatchewan before this enormous 

 barometric anomaly developed, the prevailing weather of last Sep- 

 tember and October could have been then measurably foreshadowed, 

 with almost as much certainty as, when a " cold wave " from the north 

 is moving over the Lakes any day in January, the Signal-Ofiice indicates 

 " cold weather " for the interior of the country. 



But enough has been said on this part of our subject. The neces- 

 sity of studying the atmosphere as a unit need not be further pressed ; 

 for, as Dove forcibly said, " it is, as its name shows, a great steam-ap- 

 paratus, whose reservoir is the ocean, its furnace the sun, and whose 

 condensing vessels are the higher geographical latitudes," so that only 

 when viewed as a whole can its operations be clearly understood. The 

 simultaneoiisness of the present international system insures the accu- 

 racy of the results that may be deduced. And the international chart 

 acts as a sort of lens by means of which the scattered rays of meteor- 

 ological light are concentrated in a focus upon the dark points of the 

 science. It is but just to add that the credit of originating, organiz- 

 ing, and elaborating this simultaneous system, both of the ocean mete- 

 orology and that of the land, belongs to General Myer, who, in the 

 execution of his plans, has been seconded by the indefatigable labors 

 of his assistants in the Washington Weather Bureau, and sustained by 

 the energetic cooperation of all foreign weather-services. 



The extension of this research can not fail to afford the diligent in- 

 vestigator a magnificent view of the complicate and exquisite adapta- 



