SIGNAL SERVICE. 



the clmos in which for ages it bad lain. Its 

 cardinal principle of observation is to gain a 

 daily or tri-daily view of the atmospheric con- 

 ditions and movements over the country as they 

 nrtKiilly are, and as they would bo seen could 

 they, so to speak, be photographed. In ull 

 piwious systems this was far from attainable, 

 lor lack of simultaneous reports. As formerly 

 observers had read off their barometers and 

 other instruments at the given hours of local 

 time, and not at the same moment of actual 

 time, the reports from stations at widely sep- 

 arated meridians necessarily yielded unnatural 

 and distorted representations of the phenomena 

 to be studied. The Chief Signal Officer's plan 

 reversed this vicious arrangement, and inaugu- 

 rated one by which all the weather- observers 

 over the entire field of inquiry, from the At- 

 lantic to the Pacific coast, were to observe and 

 read off their instruments " at the same moment 

 of actual (not local) time." Under the new 

 method, introduced by General Myer in 1870, 

 all the members of the Signal Corps registered 

 and reported the weather of the United States, 

 as it were, by given strokes of a single clock 

 the same moments of physical time corre- 

 sponding to certain fixed moments of Wash- 

 ington mean time. 



Simple as this innovation appears, it is vital 

 to all successful research in an aerial sea whose 

 currents and waves rush with great rapidity, 

 and perform some of their evolutions while 

 the sun in his daily march is passing from one 

 meridian to another. The old methods, with- 

 out exception, though called "synchronous," 

 were not truly so,* since each one of the ob- 

 servers reported at the local time of his own 

 special station. When, therefore, the stations 

 were extended over thousands of miles in an 

 east and west direction (as was necessarily the 

 case in the United States, owing to its geo- 

 graphical shape), their data were misleading. 

 Columbus on his first voyage to America dis- 

 covered that within the tropics the waters of 

 the ocean move from east to west; but in the 

 extra-tropical belt they move from west to 

 east. As with the waters of the sea, so with 

 the winds: from the equator nearly to the 

 polar circles the great perennial air-curivnN 

 (in which cyclones lie imbedded and in which 

 they move forward as eddies in a stream) 

 move on the surface of the earth along the 

 parallels of latitude, and but seldom along tho 



* By " synchronous " weather-reports meteorologists only 

 mean reports taken nominally at the same hour. Thus. If 

 a London observer reported the weather at 7 A. x. Greenwich 

 time, and a Berlin observer reported It at 7 A. M Berlin time, 

 the two reports would be called " synchronous " ; but, in real- 

 ity, they would not be synchronous] for the difference between 

 7 A. M. at one and the other point is about 54 minutes. But 

 54 minutes makes a great difference In the flight of a storm 

 and the shlftlnirs of atmospheric masses, which can not there- 

 fore be represented on weather-maps based upon " synchro- 

 nous" reports. A w.'iitluT-map prepared from such "syn- 

 chronous " reports reflects the aerial elements untruly, M a 

 telescopic Ions having many Irregular fares, and not a single 

 focus, would reflect the surface of the moon. " Simultaneous " 

 reports, on the contrary, when entered on a weather-map, 

 form a true mirror of "tho atmospheric masses and move- 

 ments as they are in nature. 



meridians of longitude. For this physical rea- 

 son, it was found to be of the utinust impor- 

 tance to observe these great movements at 

 many points over long portions of the par- 

 allels of latitude simultaneously. In no other 

 way can the bearings of the various storm- 

 winds and their connected phenomena be de- 

 tected, or the rates of their transition deter- 

 mined. All the predictions and deductions of 

 the Signal Office, therefore, have from its be- 

 ginning until now been based on reports taken 

 simultaneously. 



Early Developments. As the early develop- 

 ments of the Signal Service were necessarily 

 pioneer work, it being the first attempt to in- 

 stitute a system of "simultaneous" weather- 

 telegraphy, and finding many of the laws of 

 storms now defined then scarcely formulated 

 or entirely unknown, its advance in 1871 was 

 cautious and slow. But, when once it had es- 

 tablished the fact that at any hour of the day 

 or night it could almost instantly call for re- 

 ports from all parts of the country, and receive 

 them from all its stations, taken at the same 

 moment of time and revealing the actual status 

 of the atmosphere over its whole field of in- 

 quiry, the sense of security in its scientific 

 processes, and the confidence that the results 

 were built upon " the solid ground of nature," 

 gave it a powerful forward impulse. The new 

 method of simultaneous reports, it was felt, 

 was a sure road to the desired goal. In a 

 short time additional stations were established 

 within the United States, making sixty-six in 



NORTH 



SOUTH 



HORIZONTAL MOVEMENTS OF AIK AROUND CENTKU O 

 CYCLONE IN NORTHERN UEMIM'llERE. 



(Large arrow shows path of storm : snulli-r arrows* nhow the 

 course of the winds Increasing in velocity as they ap- 



i path of 

 rinda Inc 

 proach the centra.) 



all. A comparison of the tri-daily forecasts, 

 or "probabilities," as they were styled, with 

 the weather-conditions following and reported 

 as actually observed, so far as verified up t-> 

 November 1, 1871, had given an average of 69 

 per cent. From that date to October 1, 1 V 7_. 

 the average of verification rose to 76-8 per 



