June 25, 1915] 



SCIENCE 



947 



and the details of the method employed are 

 indicated. 



14. Mitosis in, Trichomonas: C. A. KoFom 

 and O. SwEZY, Zoological Laboratory, Uni- 

 versity of California. 



The authors conclude that cell-division in 

 trichomonad flagellates is a true mitosis with 

 differentiated chromosomes, which split longi- 

 tudinally prior to their location in the equa- 

 torial plate; that the nuclear membrane per- 

 sists throughout mitosis ; that the paradesmose 

 between the migrating blepharoplasts is extra- 

 nuclear at all times, disappears after nuclear 

 division, and does not give rise to the axo- 

 style; and that the axostyle splits longitudi- 

 nally and thus forms two daughter axostyles. 

 The number concludes with the report of the 

 annual meeting (which has already appeared 

 in Science) by the home secretary, and with 

 announcements of the research grants made 

 from the trust funds of the academy during 

 the preceding year. 



SPECIAL ARTICLES 



THE CONTINUOUS SPECTRA OF GASES 



In spectroscopic literature there are many 

 casual references to a continuous background 

 in the vacuum-tube spectra of various gases, 

 such as oxygen, chlorine, etc. Usually these 

 observations appear to have been confined to 

 the visible region, and I can recall no com- 

 ments on continuous spectra in the ultra-violet 

 except in the case of hydrogen. Schniederjost'^ 

 and Friederichs- observed such a spectrum at 

 low pressures, which extended to a wave-length 

 of about 2,100. The latter attempted to use 

 the uncondensed discharge through a small 

 capillary tube at about 2 mm. pressure as a 

 source for the photography of absorption 

 spectra, but found that the results were un- 

 satisfactory, even with exposures varying from 

 twelve to twenty-four hours. 



In photographs of the hydrogen spectrum 

 obtained with a large two-prism quartz spectro- 

 graph I have frequently observed this continu- 

 ous spectrum. Although the resolving power 

 of this spectrograph in the extreme ultra- 



1 Seliniederjost, Zt. f. Wiss. Phot., p. 265, 1904. 



2 Friederichs, Bonn Diss., 1905. 



violet is greater than that of a five-inch grating 

 in the first order, there is no evidence of reso- 

 lution into lines or bands. The spectrum ap- 

 pears to be uniformly continuous, and it 

 seems likely that its gradual fading out in ap- 

 proaching the wave-length 2,100 is due rather 

 to the absorption of the thick quartz system 

 than to the lack of these wave-lengths in the 

 emitted light. It appears to be due to pure 

 hydrogen, for successive improvements in 

 purity due to the removal of oxygen, water 

 vapor, and nitrogen cause no noticeable 

 change; nor does the addition of a trace of 

 oxygen to hydrogen previously freed from that 

 gas as far as possible cause any appreciable 

 difference. 



It seems very unlikely that a continuous 

 spectrum can arise from free vibrations within 

 the atom or molecule, hence it has been usually 

 ascribed to molecular collisions. In comparing 

 different gases at the same pressure, the num- 

 ber of collisions would depend mostly on the 

 mean velocity of the molecules, so that the 

 number of collisions would rapidly diminish 

 as the molecular weight increases; hence we 

 might expect that the continuous spectrum of 

 a light gas would be stronger than that of a 

 heavier gas. This was found to hold good for 

 hydrogen, helium and neon. Photographs were 

 obtained of the spectra of these three gases in 

 vacuum tubes prepared by Hilger. The pres- 

 sure was about the same in all. With a two- 

 minute exposure, the continuous spectrum of 

 hydrogen was very intense; that of helium 

 about half as strong, and that of neon about 

 one third as strong. They all extended to 

 about the same limit — that set by the trans- 

 parency of the quartz. In all these cases the 

 uncondensed discharge of a medium-sized in- 

 duction coil was used. The introduction of a 

 condenser almost completely obliterated the 

 continuous spectrum. When a condenser is 

 used the radiation probably comes from disso- 

 ciated ions, with free periods little disturbed 

 by molecular collisions. 



Nitrogen, krypton and xenon did not show 

 any continuous spectrum. 



Some tests showed that hydrogen tubes may 

 render excellent service as sources for the 



