576 CURRENT TOPICS. [J. F. I.

The Spectrum of Hydrogen Positive Rays. G. P. THOMSON. (Phil. Mug., August, Igzo.)-There are two quite different spectra obtainable from hydrogen. In one but few lines are easily ob- tainable and the wave-lengths of these are related to one another by derivation from a common formula-the Balmer series. The other spectrum has more lines and these have not been reduced to any law. The origin of the two spectra has been in doubt. Sir J. J. Thomson’s method of analyzing positive rays makes pos- sible the separation of such rays as are due to atoms from those due to molecules and the identification of each kind.

The problem attacked by the investigator was to get positive rays consisting chiefly of hydrogen atoms and to photograph their spectrum and, again to obtain rays of molecules and ex- amine their spectrum. He found that size and other geometrical relations of the apparatus affected the relative proportions of atoms and molecules. He succeeded in getting rays with few or no molecules. Such rays showed the Balmer series lines alone. He could not get rays of molecules exclusively. The best result attained was a marked preponderance of molecules. Then the spectrum was of the second kind with, of course, lines of the first plainly visible, agreeing with the known presence of atoms in the stream of rays. He concludes that the Balmer series spectrum is emitted by atoms and the second spectrum by molecules.

G. F. S.

An Economical Method of Utilizing the Force of the Tides. G. BIGOURDAN. (Comptes Rendus, July 26, 1920. j-As a result of the wanton destruction of the French coal mines by Germany the scientists of France are seeking to utilize whatever sources of energy are available in their country. In the Pyrenees and in the Alps the “ white coal ” of the waterfalls is largely used. The “ green coal ” of the tidal energy remains to be exploited, and for the industrial development of the country it is especially desir- able to do this because its chief seat is in the northwest far away from the water-power of the mountains. The author renews a suggestion made by him in 1910. Let a diving bell be fixed in the water. As the tide rises the water would ascend within it and compress the enclosed air. As the tides run out there would be an aspiratio,n of air into the bell. Both the compressed and the rarefied air could be used to transmit power. The bell would be a sort of pump in which the piston, moved by the sun and moon, makes rather more than two strokes per day. The claim is made that such an arrangement avoids the drawbacks caused by the intermittent character and the inequality of the tides and that its manipulation would be chiefly a matter of cocks and sluices re- quiring the services of but few attendants.

G. F. S.