Spectra of Hydrogen, Nitrogen and Oxygen in the Extreme Ultraviolet

Spectroscopy of Extreme Ultraviolet.---A method which has been developed of coating films with an emulsion suitable for work in this region is described in detail, and also an oil-cooled discharge tube of the internal capillary type which will stand an input of 2.25 KW and thus reduce the time of exposure and consequent fogging of the films from 10 to 100 fold. Transparency of oxygen, nitrogen and air between 500 and 1,800 {}. was investigated. In a vacuum spectrograph with a grating of 50 cm. radius these gases were found to transmit light of from 1100 to 1225 {}. even when at a pressure of 3 cm. At around 1 mm. spectrum lines were photographed from 800 to 1,800 {}. and with oxygen at 0.001 mm., the spectrum was photographed to 430 {}. These gases, then, are not as opaque to light in this region of the spectrum as has been generally supposed.Spectrum of discharge through hydrogen, 1,220 to 885 {}. The ultraviolet limit is the same for both continuous and disruptive discharges. Four spectrograms are reproduced and the wave-lengths are given for 90 lines below 1,059 {}., presumably due to hydrogen, as a continuous stream of pure gas was supplied. The resonance line was found superimposed in the fourth order on the H_β line; hence its wavelength is 1,215.68 ±{} 0.03 {}. This coincidence confirms the Bohr formula for this line, which is the first of the Lyman series.Spectrum of Discharge through Nitrogen, 1,750 to 835 {}.---The continuous discharge gives chiefly the band spectrum of nitrogen, which is extended to 1,026 {}., the wave-lengths of 19 bands below 1,385 {}A. being given. The wave-lengths of 50 new lines obtained with the disruptive discharge are also given and four spectrograms are reproduced.Spectrum of Discharge through Oxygen, 1,863 to 507 {}.---Wave-lengths of about 100 new lines obtained with a disruptive discharge are given and six spectrograms are reproduced. When mercury vapor was present about 15 additional lines extending to 433 {}. were obtained.Explanation of fluorescence observed around aluminum spark in air by Lenard in 1910, to a distance of 4 cm., may depend on the transparency of air to light of wave-length 1,000 to 1,400 {}.