798 



SIGNAL SERVICE. 



grams and Reports for the Benefit of Com- 

 merce and Agriculture." 



This was the first attempt of the United States 

 Government to inaugurate a national weather 

 service. The peculiar geographical extension 

 of the country, stretching over fifty-seven de- 

 grees of longitude and twenty-two of latitude, 

 afforded exceptional advantages for investigat- 

 ing and predicting the storms which cross its 

 broad area ; for experience and observation had 

 shown that they generally move from west to 

 east, and not frequently along the meridians. 

 But the vast extent of the storm-field, coupled 

 with the fact that the "law of storms" was 

 then but roughly outlined, made the execution 

 of this task a very difficult and tedious work, 

 calling for great caution and the most accurate 

 observations. Redfield had demonstrated from 

 ship-reports that on the sea cyclonic disturb- 

 ances in the northern hemisphere rotate from 

 right to left in a direction contrary to the 

 hands of a watch. Ferrel and others had de- 

 monstrated that, mathematically or mechani- 

 cally, this law should in theory hold good for 

 both land and sea. The Dutch investigator 

 Buys-Ballot, from actual weather-observations, 

 had shown that the law held good for Holland. 

 But its demonstration on the wider continen- 

 tal field of America, as well as the discovery of 

 many details affecting its practical application 

 to weather-prediction, awaited further, more 

 extensive, and more exact research. It was 

 not until November 1, 1870, that the Chief 

 Signal Officer was able to issue weather-bulle- 

 tins. On that day, from twenty-four stations, 

 the first systematized simultaneous reports of 

 the weather ever taken in the United States 

 were read from their instruments by the Sig- 

 nal Service observers, and telegraphed to the 

 Central Signal Office at Washington. The same 

 day the bulletins made up from these reports 

 were prepared and telegraphed by the Chief 

 Signal Officer to more than twenty cities. The 

 first storm-warning was bulletined along the 

 lakes a week later, for the benefit of the large 

 commercial and marine interests exposed to the 

 furious gales which sweep, especially in autumn, 

 over their waters. These tentative attempts to 

 introduce the novel system of practical weather- 

 telegraphy were vigorously followed up, and 

 the success realized so early in the operations 

 of the service was as gratifying to the public as 

 to the office itself. This success was due in 

 large measure to the system of observation and 

 reports being in the strictest sense simultaneous. 



Weather-Maps. To arrive at any result, it was 

 found necessary almost from the first to chart 

 weather-maps from the reports thus received 

 by telegraph. The Signal Service weather- 

 map is a map of the United States on which 

 all the Signal Service stations are entered in 

 their appropriate geographical places, and hav- 

 ing annexed to each station the figures express- 

 ing the readings of the barometer and ther- 

 mometer, the velocity of the wind, the amount 

 of rainfall within the previous twenty-four or 



eight hours, etc. ; and also symbols indicating 

 the direction of the wind, and the form and 

 amount of cloud, at the given time of observa- 

 tion. The observations taken at each station 

 are all put down on the map, and the relations 

 between them are thus made sensible to the 

 eye of the Signal Officer, by the figures ;i:ul 

 symbols, and also by lines drawn to group 

 the geographical areas over which like con- 

 ditions prevail. The weather-map is, there- 

 fore, to the meteorologist what the telescope 

 is to the astronomer an indispensable means 

 of obtaining a survey, and prosecuting a care- 

 ful and connected study of the phenomena he 

 seeks to understand. The accompanying " War 

 Department Weather-Map," prepared by the 

 Signal Service, illustrates the method of chart- 

 ing the map graphically. This specimen map 

 is about three eighths the size of those from 

 which the Signal Office works. It represents 

 the atmospheric conditions as they were simul- 

 taneously observed at 7 A. M. mean Washing- 

 ton time, December 23, 1879 : the area marked 

 " LOW " defining a storm or cyclonic area in 

 Texas with low pressure, and that marked 

 " HIGH " defining the limits of an anticyclonic 

 area, in which the barometer .is high. Around 

 the latter the winds are seen to draw in the 

 direction of the hands of a clock ; but around 

 the former, in a contrary direction. 



Simultaneous Weather- Observations. In or- 

 ganizing this service, the first problem that pre- 

 sented itself was to devise a system of observa- 

 tions which would when mapped accurately 

 represent the aerial phenomena in their actual 

 relations to each other, and thus enable the in- 

 vestigator to discover the laws of storms and 

 their rates of movement over the earth's sur- 

 face. " The history of science," says one of 

 its foremost representatives, "proves that un- 

 connected, unsystematic, inaccurate observa- 

 tions are worth nothing." Certainly, in the 

 domain of meteorology, no solid foundation for 

 the science of the weather could have been laid 

 in 1870 upon any of the then existing observa- 

 tional systems. The European weather-stations 

 at that date, and long after, were engaged in 

 making non-simultaneous reports; no two of 

 them, unless they happened to be on the same 

 meridian, read off their instruments at the same 

 time ; and consequently their records, valuable 

 as they were for purposes of local meteorology, 

 were inadequate and untrustworthy for pur- 

 poses of rigidly scientific comparison, or for 

 giving accurate numerical data of changes in 

 the ever-restless and fickle atmospheric ocean. 

 In this state of the research, which had made 

 meteorology a proverb for inexactness, General 

 Myer proposed a new, independent, and origi- 

 nal system of investigation the system of 

 SIMULTANEOUS METEOROLOGY on the results 

 of which the weather-predictions and storm- 

 warnings of the Signal Service have been based 

 from the beginning of its work until now. 



This novel, yet perfectly simple, scheme 

 aimed at the rescue of weather-research from 



