578 CURRENT TOPICS. [J. F. I.

of the gust would force the flying organism downward and not up- ward. Ascending air currents are ruled out as a cause since inland soaring birds avoid them so long as the sun shines. There is some reason to hold that the turbulence of the air may be a factor in soaring flight, but the burden of the evidence is against it. A soaring dragon- fly may be seen gliding in the midst of a group of flapping flies. " What form of pre~xisting air movement can be imagined that pro- pels the soaring dragon-fly and yet has no effect on the flapping dragon-fly, though the latter is of lighter weight and loading ? "

Having demolished all suggested explanations the author con- cludes " that soaring flight is inexplicable in the light of existing knowledge," and suggests that experimental investigations be under- taken, since observation alone has failed to furnish the solution of the enigma.

In India the boys play with a puttung, a kite made of paper and bamboo. In a proper wind this flies stably at the top of a vertical string. In this particular, as well as in others, it shows itself akin to the soaring of birds and suggests itself as a promising beginning for an experimental attack upon the problem.

G. F. S.

F. W. ASTON and G. P. THOMSON announce, in Nature, Feb- ruary 24, I921 , that their exper imen t s wi th posi t ive rays show lithium to be composed of two isotopes having the atomic weights 6 arid 7, respectively. The former preponderates. The relative pro- portions of the two correspond to the atomic weight of lithium, 6.96.

G. F. S.

Efficiency in Indus t ry . (Nature, February 24, I 9 2 I . ) ~ T h e Daily Mail of London recently organized an exhibition for the pur- pose of emphasizing the advantages of applying scientific principles and results to industry. On the historical side the University of Lon- don presented the development of the thermionic valve from the lamps of 1887 made with internal plates by J. A. Fleming to study the Edison effect up to the most recent type of valve. There was also on exhibit apparatus used by Sir William Ramsay in his study of the rare gases as well as electrical apparatus employed by Clerk Maxwell.

A wireless set was shown, weighing 20 po.unds only, yet capable of receiving messages from continental stations. Chance Brothers exhibited " Crookes " glass for protecting the eyes. This absorbs the ultra-violet part of the spectrum while allowing the visible spectrum to pass. Various devices were shown by which colors can be matched in artificial light.

The range of the exhibition was much wider than would he in- ferred from the exhibits just cited. The interest manifested is indic- ative of the growing appreciation in Great Britain of the importance of science to national welfare in peace as well as in war.

G. F. S.