380 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



turned on. By continuing his observations he found that rays of 

 unknown nature were traveling in straight lines from the discharge 

 tube and that when solid objects were interposed they threw a 

 shadow on the screen. He also observed that these unknown rays 

 could easily pass through objects of low density such as a wooden 

 door and that they then could affect a photographic plate, making a 

 record on it of the internal structure of the object. Everyone is 

 now familiar with the practical value of X-rays and is aware of 

 the important part which they play not only in medical practice 

 but also in scientific and industrial work. 



The existence of cosmic rays was not discovered until 1900. 

 Physicists found that when gas is enclosed in a hollow steel ball, 

 rays of some sort pass through the metal shell of the ball and steal 

 electrons from some of the gas atoms, or cause ionization of tlie gas. 

 It was later learned that some of this penetrating radiation was 

 made up of rays from radium in the rocks of the earth's crust. The 

 radium-born rays could be prevented from reaching the interior of 

 the ball by surrounding it with a layer of lead, just as X-ray treat- 

 ment rooms are encased in lead to prevent the outward passage of 

 X-rays. When the ball was encased in lead, however, numerous rays 

 of energies much greater than radium emanations and X-rays still 

 penetrated the interior and ionized the gas. These are the cosmic 

 rays now believed to be charged flying particles that cannot be seen 

 and are known only by their effect. Although the cosmic rays pour 

 in on the earth, only the strongest of them can register their existence 

 inside steel balls at the earth's surface. Since their discovery, 

 scientists have been piecing together facts about the cosmic rays and 

 are especially eager to learn about those in the thin rare atmosphere 

 where they are most numerous and stronger before they have been 

 exhausted by the comparatively heavy gases near the earth. The 

 stratosphere balloon is the only means by which scientists can as- 

 cend to the stratosphere, 8 miles above the earth, and measure these 

 cosmic rays. 



Here at the Smithsonian Institution interesting and diversified 

 experimentation is now in progress. With the assistance of Mc- 

 Alister (1933) the following researches in the field of ultraviolet 

 have been conducted. Algae have been irradiated with ultraviolet 

 rays by Meier (1936). In the regions where the ultraviolet was of 

 shorter wave length than that found in solar radiation the green 

 plant cells were killed. The certainty of the action as well as the 

 speed of the attack of these rays has been determined. 



Friedmann (1935) started interesting experimentation on the 

 potentialities of the secretion of the preen gland of the house sparrow 

 and of the starling. Extract of the preen gland was irradiated with 



