The secondary spectrum of hydrogen at higher pressures

Among the numerous methods that have been employed for investigating the secondary spectrum of hydrogen, use has not been made until recently of the arc spectrum at higher pressures. A beginning was made by Kiuti, who discovered a Q series which he correlated with the Fulcher Bands. The author has photographed the spectrum given by an arc between tungsten electrodes in an atmosphere of hydrogen, and has found that the intensities of the lines differ considerably from those given by Merton and Barratt. The method seems to present the possibility of detecting regularities among the lines. The question of whether the interpretation given to the series found is the correct one must, however, remain open to further experimental investigation.The Blue Region .—One of the most prominent features of a plate embracing the region 4450—5000 A. U. is an aggregate of strong lines closely resembling a band with head at 4582·58 A. U., and shading towards the violet. Many of these lines are shown by Merton and Barratt as high-pressure lines, and the majority are marked as not showing the Zeeman effect. An attempt has been made to classify these lines into a P, Q, and R combination. If our interpretation of this band is correct, it is characterised by a strong Q series having the lines corresponding to even quantum integers stronger than those corresponding to odd, and by a short P branch.