Terrestrial Helium (?)

Abstract

PROF. PASCHEN and I have lately made a careful determination of the wave-length of the strong yellow line emitted by cleveite when heated in a Plücker tube. We owe the mineral to the kindness of Prof. Rinne. My large Rowland concave grating of 6˙5 metre radius, clearly shows the yellow line to be double. Its less refrangible component is much weaker, but comes out quite bright, when the stronger one is brilliant. We photographed the two lines together with the second order of the spark spectrum of iron. There are a number of iron lines on each side that are included in Rowland's list of standard wave-lengths (Phil. Mag., July 1893). From these we interpolated the wavelengths of the yellow lines by micrometric measurement. Three different plates taken on different days gave us: We think an error of more than 0˙025 very improbable.