l6 L. VEGARD. M.-N. Kl. 



ture which is necessary to make the Nitrogen pressure at 600 km. equal 

 to a given pressure. 



From table IV we see that for a temperature of 200° absolute, the 

 pressure of Nitrogen already at a height of 130 km. is only 0,0026 dyn/cm^. 

 If a Nitrogen pressure of this magnitude should exist at a height of 600 km. 

 the corresponding temperature T can be found from equation (2) by putting 

 // = 130, /i„ = 10, T= 220", // = 600 and we get: 



T= 1078' abs. 



That the atmosphere above 10 km. should have a temperature of this 

 magnitude must, I think, be considered as excluded. 



The simplest wa\' in which to prevent the Nitrogen density from dimin- 

 ishing so rapidly as we pas upwards in the auroral region, would be to 

 suppose that the upper strata were electrically charged, and consequently were 

 acted on by electric forces. We might suppose the gas near the limit of the 

 atmosphere partly to exist as positive ions. This is, in fact, what we should 

 expect from a physical point of view. The upper layers of the atmosphere 

 are exposed to the direct action of the suns radiation. On account of the 

 photoelectric effect, electrons will be driven out from the gas molecules 

 with maximum velocities determined by the Einstein equation: 



(6) - ;// -c- = h r 



2 



where v is the maximum frequency of the incident light, and /; is Planck's 

 constant. 



Now it is prety certain that the sun — besides the ordinary light 

 spectrum — emits radiation of much shorter wa\-elength of the type we 

 know from the A'- and y-rays. With energy-quanta of this magnitude, 

 electrons may be driven out of the atmosphere from quite a considerable 

 layer of gas round the earth, leaving the gas molecules behind in the form 

 of positive ions. 



In this way a positively charged shell will be kept round the earth. 

 Above a certain heigth the electric force will be directed upwards, and 

 below this heigth it must, on account of the negative charge of the 

 earth, be directed downwards. 



The variation of pressure will no longer be given b}' the equation: 



(7) dp = — gg d/i 



but instead of this we nov get for higher strata: 



(8) • dp = —{og—oF](//i. 



Where n is the electric charge per unit volume and F the electric force. 

 The electric charge will diminish the weight of a given quantity of gas; it 



