•JO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



to the resultant influence on man's welfare in the higher altitudes. 

 These other qualities have a special influence on pulmonary tubercu- 

 losis and should be recognized in estimating the effect on patients 

 of this class. 



We have, first, greater insolation. The part played by the earth's 

 atmosphere in arresting the sun's rays is very important and second 

 only to the influence of the atmosphere of the sun itself in arresting 

 the radiation of light and heat from the sun. Slight changes in the 

 sun's atmosphere would speedily alter the terrestrial climate. On 

 the earth's surface at sea level the energy of light of the sun and that 

 of the heat rays are considerably less than at the higher altitudes and 

 recent measurements are of great interest and practical value. 



Dr. Julius Hann, the great meteorologist of Vienna, has noted that 

 on the lower plains thirty to forty per cent of the total amount of 

 the sun's heat was absorbed by the earth's atmosphere, whereas at 

 the summit of Mt. Blanc, at 15,730 feet (4,810 meters) elevation, 

 nearly one-half of the absorbing mass of the air is lost and the 

 amount of the sun's heat absorbed was not more than 6 per cent. 

 One can readily understand that when the resistance is removed 

 the light rays are more effective than at sea level. The late Prof. 

 S. P. Langley showed by delicate measurements at this height that 

 the blue end of the spectrum grows to many times its intensity at sea 

 level." This marked diathermancy of the atmosphere goes hand in 

 hand with altitude. The increased facility with which the solar rays 

 are transmitted through an attenuated air accounts for the tan and 

 sunburn so readily acquired on mountain tops and this quality is, in 

 the author's opinion, of value in the prevention and treatment of 

 tuberculosis. 



Owing to the increased diathermancy of the atmosphere at ele- 

 vated stations there is a remarkable difference between the atmos- 

 pheric temperature in the sun and in the shade. At the higher Alpine 

 resorts for tuberculous patients, such as Davos (5,200 feet), St. 

 Moritz (6,000 feet), Arosa (6,100 feet), and Leysin (4,757 feet), 

 the excessive heat in the sun compared with shade temperatures in 

 winter favors the outdoor life during the " invalid's day." It also, 

 mcidentally, impresses all newly arrived visitors as a marvellous cli- 

 matic feature. At St. Moritz, now a fashionable winter resort, ladies 

 find parasols almost a necessity while friends are skating, and those 



^ S. P. Langley : Researches on Solar Heat and Its Absorption by the 

 Earth's Atmosphere. Papers of the U. S. Weather Bureau, No. 15, Wash- 

 ington, 1884, p. 242. 



