NORTHERN LIGHTS— EVE 155 



recorders, was 231/2 miles, at Padua. One of Regener's balloons has 

 ascended 17i/^ miles and been recovered with its recorders. 



In recent years attempts have been made to explore the strato- 

 sphere in balloons. The intrepid Piccard constructed a gondola 

 sufficiently strong not to explode outward, and was himself carried 

 inside it upward by a balloon. The ascent is easy, the place and 

 nature of arrival on the earth are largely fortuitous. He reached an 

 altitude of 10 miles and obtained valuable results on the cosmic rays, 

 which at that height are about 100 times as intense as on the earth's 

 surface. The Soviet gondola crashed to disaster after attaining an 

 altitude of 12 miles. The greatest height so far attained is 131/2 

 miles, achieved last year by Anderson and Stevens in the United 

 States. 



A new method of exploration has recently been devised by Tuve 

 and others, members of the Department of Terrestrial Magnetism, 

 Carnegie Institution of Washington. A searchlight beam is directed 

 upward to a height of 17 to 40 miles, and the intensity of the light 

 is modulated, or varied periodically at the source. A large concave 

 mirror collects the scattered light from the upper part of the beam 

 and brings it to a focus on a photocell connected to an amplifier, 

 which is synchronized with the modulation of the searchlight. This 

 apparatus may well give some information on the nature of the 

 molecules in those very regions on which we are least informed, 

 above the range of pilot balloons and below the auroral and ozone 

 layers. 



Ozone, O3, is produced from oxygen, O2, by radiations of a suit- 

 able frequency or by electrical discharges. Much of the ultraviolet 

 light from the sun is absorbed or stopped in the ozonosphere about 

 20 to 40 miles above the earth. The presence of the ozone is revealed 

 by absorption bands in the spectrum of the sun. When the sun is 

 high it passes almost vertically through the ozone layers. When 

 the sun is setting its rays have to pass horizontally through a much 

 greater thickness. Measurements of the intensities of the absorp- 

 tion lines due to ozone lead to an estimate of the height of the ozone 

 region as being about 25 miles, and therefore lower than the Northern 

 Lights. 



The barometric disturbance due to the great Krakatoa volcanic 

 explosion traveled four times round the earth, and the actual noise 

 of it was heard 3,000 miles away. The sound of big guns or of heavy 

 explosions passes upward into the cool and rarefied air and is then 

 refracted or bent back again to the earth, so that sometimes, like 

 short-wave radio, it cannot be heard or detected at intermediate 

 distances, Newton stood in the gateway of Trinity College, Cam- 

 bridge, and heard the guns of the naval action between the Dutch 



