124 Scientific Intelligence. 



complete disappearance of the oxygen which has a relatively 

 large mass after numerous resuscitations of a given tube. 



A recapitulation of the more important facts brought out by 

 Paschen's investigations will now be given. The spectrum of 

 helium consists of two o series whose respective fundamental lines, 

 at 10830 A and 20582 A, comprise by far the greatest proportion 

 of the total radiation. Pure helium gas in the positive column 

 of the glow discharge or in other parts of a Geissler tube absorbs 

 the energy of the two infra-red lines at current densities as low as 

 10~ 7 amperes per cm 2 . For such currents the intensity of emission 

 of the infra-red lines and of the visible lines is barely noticeable. 

 In this connection, it is especially worthy of note that a current 

 must be sent through the gas in order to start absorption. In this 

 respect helium differs from the vapors of sodium and mercury. 

 It is shown by curves that, as the electric current is increased in 

 strength, the line absorption increases very rapidly at first and 

 then gradually rises asymptotically towards a superior limit. 

 The lines in the visible spectrum first exert measurable absorption 

 when the current is about 10,000 times as great as is required to 

 produce observable o absorption by the two fundamental lines. 

 The line at 10830 A possesses the majority of the energy of the 

 entire spectrum. With a column of gas 30 cm long the line absorp- 

 tion attains the value 95 per cent. The detailed investigation of 

 the question concerning what becomes of the energy absorbed, 

 brought out a most interesting and important fact relative to the 

 resonance radiation of the strongest line 10830 A. It was 

 found that a resonator is present in the helium atom having the 

 property of again radiating into space all of the energy which it 

 had absorbed. This discovery affords the first concrete example 

 of the type of electric resonator introduced by Planck in his 

 remarkable theory of radiation. On the contrary, the second 

 fundamental line, at X20582, has not as yet shown a detectable 

 amount of resonance radiation, in spite of the fact that it exerts 

 strong absorption. Finally, Paschen investigated the tempera- 

 ture of a black body which would radiate X 10830 with the same 

 intensity as does helium gas. In this sense, a lower limit for the 

 "temperature of the monochromatic radiation" of helium is 

 obtained. The values found were 7890° and 9580° C. absolute, 

 according to the current sent through the Geissler tube. — Ann. 

 d. P/u/sik, vol. xlv, p. 625, October, 1914. h. s. u. 



6. Intermittent Vision. — In a paper communicated, in the 

 year 1913, to the Royal Society by Mallock, in order to account 

 for the intermittences seen when observing a revolving disc of 

 black and white sectors, at the instant when a slight mechanical 

 shock is given to the head or body, the hypothesis is advanced 

 that a slight mechanical shock of any kind produces a periodic 

 but rapidly extinguished paralysis of the perception of light, and 

 that the nerves on which seeing depends cannot bear more than a 

 certain amount of mechanical acceleration without loss of 

 sensibility. This phenomenon has been recently subjected to 



