WEATHER BUREAU. 13 



hydrogen and with instrument makers and special aeronautic experts 

 in the United States and Europe, in order to ascertain what is at pres- 

 ent considered practicable and best. There is every prospect that we 

 shall be able to send up some sounding balloons with meteorographs 

 during the coming year. Meanwhile the most laborious part of the 

 preparatory work falls upon Professor Marvin and will take nearly all 

 of his time for six months to come. 



SOLAR HEAT AND ATMOSPHERIC ABSORPTION. 



In July, 19U1, the Bureau received three copies of Angstrom's 

 Electric Comj)ensation Pyrheliometer, which instrument is intended 

 to measure in calories the amount of heat received by radiation from 

 any distant source, including, of course, the sun. It is intended to 

 use these three instruments in carrying out researches on the amount 

 of solar heat and of atmospheric absorption and allied questions. One 

 of them is kept as a standard at the Weather Bureau and may be used 

 in Washington ; the others are now located, respectively, in Balti- 

 more, in care of Prof. J. S. Ames, and the other in Providence, R. I., 

 in care of Prof. Carl Barns. Numerous investigations must be car- 

 ried on by these physicists as preliminary to the main object of our 

 research. Articles published in the Monthly Weather Review by 

 Prof. C. F. Marvin and Prof. F. W. Very, and by Mr. C. G. Abbott 

 and Prof. S. P. Langley, have given a general idea of the scope that 

 the investigation must take. 



BAROMETRY. 



The work on the barometry of the United States and Canada has 

 been completed by Prof. Frank H. Bigelow, and tlie tables for the 

 reduction of sea level have been in operation since January 1, 1902, 

 with results which seem to be quite satisfactory. The work of i^re- 

 paring and checking the station tables for reductions to the 3,500-foot 

 and the 10,000-foot planes is complete, and the individual tables will 

 be issued during July, to be expanded at the stations, so that they 

 will be ready for use in the autumn, as soon as the circulation begins 

 to be vigorous. 



NEPHOSCOPIC ORSERVATIONS. 



A very valuable set of nephoscope observations in the West Indies 

 Islands has been secured, beginning May, 1899, and extending to May, 

 1902, at 11 stations. The circulation of the atmosphere in the tropical 

 zone has never been carefully mapped out, and these observations for 

 the first time afford us the necessary data for discussing these prob- 

 lems. In view of the popular interest in the distribution of the 

 ashes ejected from the volcanoes in May and June, it is very oppor- 

 tune that the prevailing currents of air in the upper strata should be 

 accurately determined. The computations on this work have been 

 begun. Similarly, nephoscope observations will soon be commenced 

 in the Pacific and Plateau districts, in order to supplement those 

 made in 1896-97 for the international commission. 



VAPOR TENSION AND PRECIPITATION. 



It has become necessary to discuss the Weather Bureau observa- 

 tions on the vapor tension throughout the United States, in view of 



