370 
PHYSICS: T. LYMAN 
graphic plates prepared exactly as recommended by Schumann. The 
wave length 600 represents an extension beyond Schumann's limit greater 
than that which Schumann himself achieved beyond X 1850. 
The relations of the spectra of hydrogen and heHum have recently 
come into prominence through the theoretical researches of Bohr, Nich- 
olson and others. It so happens that the region on the more refrangible 
side of wave length 1250 offers an important ground for the study of 
these relations. In order that the conclusions may be of value, however, 
it is necessary that the gases under observation should be free from im- 
purities. In the best form of closed discharge tubes the difficulties aris- 
ing from the contamination of the gas by the material of the tube or by 
the electrodes, are very considerable, especially when a disruptive dis- 
charge is used. In my apparatus, where the brass spectroscope and 
quartz discharge tube communicate directly, these difficulties are con- 
siderably increased. I trust in time to overcome them; but for the pres- 
ent I must confine myself to the following statements: 
Prominent in the spectrum of hydrogen is the line at 1216 which forms 
the first member of a series predicted, on theoretical grounds, by Ritz. 
I have also found the two next members near wave length 1026 and 972. 
With hydrogen, they are best seen when a disruptive discharge is used, 
but with helium containing that trace of hydrogen so difficult to remove, 
they occur quite strongly with a simple alternating current from a 60 
cycle transformer. This is a good illustration of the curious behavior 
of helium, for an atmosphere of this gas seems sometimes to faciHtate 
the production of the spectra of other gaseous substances which occur in 
it as impurities. As far as I am able to observe with the uncondensed 
discharge, all the lines seen with helium are also found in hydrogen. It 
is only with the disruptive discharge that the new fines on the more 
refrangible side of X 900 make their appearance; they occur in hefium 
alone and number seven or eight; some are qmte strong. 
The wave length of the X-rays as determined by the Braggs, is of the 
order of one angstrom unit. There is, therefore, a gap of some six 
hundred units between the region of the ordinary Rontgen rays and 
the fimit which I have reached. Several attempts have been made 
recently to produce less refrangible X-rays,^ but there is no satisfactory 
way of estimating their wave length unless perhaps one refies on the 
Planck-Einstein formula Ve = hv. Taking V as the potential drop 
which gives the cathode particle the velocity necessary to produce a very 
soft X-ray, e as the charge on the particle and giving to h the usual 
value ascribed to Planck's constant, the experiments of Dember^ were 
made to yield a wave length for the X-ray longer than that which I have 
