146 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193G 



diameter. If my audience were similarly dispersed, and if you take 

 your diameter as one foot, then your nearest neighbor would be 100 

 yards away, so that the audience would be widely scattered and in 

 an extreme state of agitation. The sound waves of the speaker are* 

 faithfully transferred to your ears by this wild jumble of swift 

 molecules. There is the further demand of intelligence, the supreme 

 factor in physics, on the part of the audience and the lecturer! In 

 the meantime there are not only a gravitational field and a magnetic 

 field throughout the region, but all the electromagnetic waves, radio 

 or wireless waves, from nearly all the broadcasting stations of the 

 world, are coming through the walls and through our bodies almost as 

 if we did not exist, making the electrons in our conducting bodies 

 dance rhythmically up and down, so that each one of us is an aerial, 

 but most fortunately, I think, we are not gifted with receiving gear 

 to detect this medley. We have to content ourselves with that wonder- 

 ful octave of electromagnetic waves which gives us the giory of light 

 and the splendor of color. 



Do not forget that from the cosmos there come also radiations 

 which can penetrate the whole atmosphere (equivalent to 30 inches of 

 mercury), pass through the roof, through our bodies, very many a 

 second, and plunge down into the earth. As was shown recently in 

 the underground railway at Holborn, even after passing through 

 more than 70 feet of solid ground, there still remains 15 percent of 

 the cosmic rays. On the whole, this theater is a much more lively 

 spot than a casual glance would suggest. 



The upper atmosphere consists of air molecules similar to those 

 around us, but, at the reduced pressure of high altitudes, the mole- 

 cules are much further apart, their free paths are much longer, so 

 that collisions between the molecules are less frequent. The differ- 

 ence between the two elevations cannot be better illustrated than by 

 the passage of electricity between two conducting regions. At our 

 level there is a more or less noisy spark, or a flash of lightning with 

 a peal of thunder. Although it is not possible to go many miles 

 aloft, it is possible to send a current of electricity between two metal 

 electrodes and to observe the changes that take place as the air is 

 pumped from a closed tube of considerable length. On making the 

 experiment there is at first little or no current ; the air acts almost as 

 an insulator. On reducing the pressure there is a thin rosy line of 

 light which grows and fills the tube until a considerable current is 

 carried by charged molecules, or ions. It is unnecessary to recall at 

 the present moment all the successive changes, but it will be seen that 

 with a high vacuum a greenish light suffuses the whole tube, because 

 electrons are taking a large share in the proceedings, and you will 

 note that they may be deflected by a magnet. 



