November ii, 1920] 



NATURE 



343 



composed of 4 hydrogen atoms and 2 negative elec- 

 trons, then vanadium should have 51 hydrogen atoms 

 and somewhere about 34 negative electrons. 



The elements beryllium, neon, magnesium, silicon, 

 chlorine, and argon'do not seem to come properly in 

 the curve. If their atomic weights have been cor- 

 rectly determined, then there must be something 

 peculiar about these elements. 



I have also drawn a curve from the atomic weights 

 as given in Bloxam's "Chemistry," hydrogen being 

 taken as i, and have produced a similar curve to the 

 one given here, except that the latter part does not 

 rise so steeply. S. G. Brown. 



52 Kensington Park Road, W.ii. 



Chemical Warfare and Scientific Workers. 



Like Prof. Soddy (Natlke, November 4, p. 310), 

 I have received an invitation from the War Office to 

 become an associate member of the "peace" organisa- 

 tion which is to "develop to the utmost extent the 

 offensive and defensive aspects of chemical warfare." 

 1 have had enough practical experience of the experi- 

 mental side of chemical warfare to know what it in- 

 volves, and I have without any hesitation refused to 

 join the new Committee. 



In the first place, the project is simply wicked. 

 Education stands for something more than the 

 acquisition of knowledge, and if at the present time 

 I lent any support to the activities of the Committee 

 I feel that 1 should necessarily be quite unfit to take 

 any part in the training of young minds. To do what 

 I ian to promote in everyone the faith that war is 

 done with has become part of my business because it 

 is the world's business. In the second place, the pro- 

 ject is futile. No real progress will be made in dis- 

 covering new methods of offensive chemical warfare 

 except by people who have their heart in it ; perfunc- 

 tory adhesion to an official organisation will discover 

 nothing worth knowing. 



Is any intelligpnt person — and only intelligent people 

 would be of anv use in this very complicated subject — 

 at this point in the world's progress going really to 

 put his heart info the search for methods of killing 

 other people? I think not, even in the case of pro- 

 fessional soldiers. Some may comfort themselves with 

 the idea that thev will escape the moral difficulty by 

 engaging only wfth defensive methods. This wifl be 

 equally futile, for adequate defence can only follow 

 discoveries on the offensive side ; it cannot precede 

 them. It is impossible to devise protection against 

 offensive qgents which are unknown, just as on the 

 medical side it is impossible to work out methods for 

 the cure of lesions of an unknown nature. The only 

 effective preventions and cures which can be prevised 

 are ethical, and a War Office Committee is not quite 

 the best atmosphere for that. 



It may be extravagant to expect that all civilians 

 will refuse to support this part of our " peace organisa- 

 tion." but I hope they will. A. E. Boycott. 



University College,' Gowcr Street, W.C.i, 

 October 5. 



Testing Einstein's Shift of Siiectral Lines. 



A WORD of caution mav not bo amiss in respect of 

 the suggestion made by Sir Oliver Lodge in Nature 

 of October 2S, p. 280. The rotational stresses in the 

 disc, though very large, may not portend immediate 

 dissolution in steel, but what of the glass (?) of the 

 v.ncuum tuf>es? The stresses, like the gravitational 

 effect, increase as (he square of the angular velocity. 

 The method would seem well calculated to develop 

 pleochroic effects in glass. Chari.RS Chrrk. 



October 30. 



NO, 2663, VOL. . 06] 



Contractile Vacuoles. 



Co.NTRACTiLE vacuoles are found only in those cells 

 which lack a continuous cell-wall. This appeared to 

 suggest that the function of the contractile vacuole 

 is to eliminate dissolved crystalloids and so to keep 

 down the osmotic pressure distending the semi- 

 permeable protoplasm. Otherwise the latter, lacking 

 the support which a continuous cell-wall gives, would 

 continue to stretch and would finally rupture. 



There is, however, another, and possibly more 

 plausible, point of view, namely, that the contractile 

 vacuole is, in point of fact, this rupture. Suppose 

 a small accumulation of a soluble crystalloid in_ a 

 semi-permeable gel which exhibits slight elasticity 

 and slight tenacity — qualities which the protoplasm 

 of the cell appears to possess. The osmotic pressure 

 of the crystalloid will push back the protoplasm, over- 

 coming its rigidity. Thus a cavity is formed which 

 enlarges as water flows into it. Expansion will pro- 

 ceed until but a very thin film of protoplasm separates 

 the solution from the surrounding water. Later 

 expansion causes continued thinning of the film until 

 its tenacity suddenly gives way, and the solution con- 

 tained in the vacuole becomes, through the rupture, 

 continuous with the surrounding water. The elasticity 

 of the protoplasm now assorts itself, and the walls 

 of the cavity are driven together. The semi-fluid, 

 viscid constituents of the protoplasm secure the 

 healing up of the rupture and the obliteration of the 

 cavity, while the viscosity of the surrounding sub- 

 stance leads to a delay in recovery marked by the 

 appearance of the radiating canals. 



Thus we mav look upon a contractile vacuole, not 

 as an organ of a cell, but rather as the effect of the 

 local accumulation of any soluble subst.nnce. In 

 fresh-water naked protoplasmic organisms the forma- 

 tion of a cavity surrounding this accumulation and 

 the periodic forcible ejection of seme of the solution 

 are rendered inevitable by the physical properties of 

 protopl.-ism. When once a cell acquires a complete 

 cell-wall, the protoplasmic film receives sufficient sup- 

 port and the vacuoles become permanent. 



TIknrv H. DtxON. 

 School of Botanv, Trinity College, Dublin, 

 October 22. 



Visibility of the Landscape during Rain. 



On a recent visit to the mountains of Nortli Wales the 

 writer was impressed with the variations in the visibility 

 of the landscape when rain was falling. In the lower 

 valleys a storm which may be sufficient to wet thick 

 clothing throvAgh in a few moments may leave the 

 contours of the mountains quite distinct at several 

 miles distance. On the other hand, a mountain 

 drizzle or " Scotch mist " may render everything in- 

 visible at a few yards. An elementary treatment of 

 the subject brings out one or two points of interest. 



Let it be assumed that the raindrops are perfectly 

 opaque and that the atmosphere is otherwise per- 

 fectly transparent, both assumptions being, in peiieral, 

 close approximations to the actual state of affairs. 



Consider a heavy rainstorm during which rain falls 

 at the rate of i cm. per hour, or 0-00028 cm. per 

 second. The raindrops anpear to be most often of 

 I to 2 mm. diameter. Taking the lower value (i mm), 

 the volume of the drop is 0-5x10-' c.c. 



According to Stokes's law 



and at tj** C, <f, the viscosity of air, is 181 x to-*, 

 so that r = 3000 cm. per sec. 

 Consequently, the depth of water which falls In 



