302 POPULAR SCIENCE MONTHLY. 



particularly valuable for determining the effects of the friction of the 

 ground on the winds, and for testing quantitatively the theories of the 

 air circulation which have heretofore depended mainly on qualitative 

 generalities. 



The decrease (and in the abnormal cases, the increase) in tempera- 

 ture with height above the ground has been carefully studied, and 

 especially in the various phases which occur under different typical 

 atmospheric conditions. The diurnal changes of temperature at differ- 

 ent altitudes have been also carefully studied. The determination of 

 the numerical values of these elements is very important in helping 

 to complete the theories of the atmospheric circulation, solar insola- 

 tion, and the transference of heat from the earth to the air. 



The rate of change of relative humidity with change of altitude, 

 due to vertical change of temperature, is very important in connection 

 with the calculation of the heights of clouds by computing the altitude 

 of the dew point temperature under known conditions near the ground ; 

 and the Blue Hill observations not only offer data for increasing the 

 accuracy of these calculations, but also a criterion for testing their abso- 

 lute accuracy. 



Until 1886 the only weather map in the United States was printed 

 at the Chief Signal Office in Washington, but in May of that year Mr. 

 Eotch with the assistance of Mr. Cole, the government observer in Bos- 

 ton, began to chart the 7 a. m. reports that were received there, and 

 manifolded the map by the cyclostyle process. This was the origin of 

 the daily weather map that is now issued in great numbers from many 

 of the Weather Bureau Stations throughout the United States. 



From 1887 until 1891 local weather forecasts were furnished by the 

 Blue Hill Observatory to the Boston press and announced from the 

 observatory by the display of weather signals. These weather predic- 

 tions were undoubtedly a considerable improvement over those made in 

 Washington, which depended on the weather map alone, especially for 

 the twenty-four hours immediately succeeding the time of observation, 

 and the demonstration of this, in direct competition with the Weather 

 Bureau predictions, probably had some effect in causing the government 

 service to appoint local forecast officials to supplement the general 

 predictions made at Washington. It must be borne in mind in this 

 connection, that this combined method of making weather predictions 

 has been, in a measure, practically carried out in European countries 

 ever since an international telegraphic exchange of weather observa- 

 tions went into effect. In this country, however, we had learned to rely 

 too much on the general predictions issued from Washington. 



There can be no doubt that the work of the Blue Hill Observatory 

 has had a very great quickening influence in the recent developments 

 in observational meteorology in this country. Not only has its thor- 



