Feb. 



1 886] 



NATURE 



357 



the time it becomes disk-shaped the drop is full of vortex- 

 motion, the disk must break up — for it is an unstable arrange- 

 ment of vortex-motion — and assume the stable arrangement, 

 namely, that of the anchor-ring. Then the most important 

 |)roperty of the liquid involved is its viscosity. If this is too 

 small, the vortex-motion will not have time to spread far by the 

 time the drop has become disk-shaped ; whilst if the viscosity is 

 too great, the vortex-motion will all be di;sipated before the drop 

 becomes disk-shaped. 



To avoid complication, experiments were made in which 

 drops were let fall into liquid of the same kind as that com- 

 posing the drop. Liquids so treated were found to arrange 

 themselves into four classes, distinguishable by the character of 

 the ring formed. The quotient ;u/p was determined for each of 

 the liquids — p. being the coefficient of viscosity found by 

 Poiseuille's capillary tube method, and p the density, water 

 being the standard in both cases. It was then found that the 

 four classes were also distinguishable by the value for jn/p. 



Thus in Class I. ether, chloroform, and carbon bisulphide 

 give rings only very uncertainly, the drop breaking up and 

 spreading irregularly through the column of liquid. For these 

 fujp is not greater than O'y. 



To Class II. belong water, alcohol, turpentine, paraffin, and 

 other liquids ; these give the best rings : and for them the value 

 of nlf is between i and 3. 



For Class III. fi/p is between 3 and probably 8 or 10 : and this 

 class includes moderately viscous liquids, such as butyl-alcohol, 

 amyl-alcohol, fairly strong sulphuric acid, and diluted glycerine. 

 In these cases the rings form very slowly. 



Class IV. includes all the most viscous liquids, like strong 

 solutions of sugar, potash, sulphuric acid, glycerine. The value 

 of ju/p is much larger (about 15 to 30), and no ring is formed at 

 all, unless special precautions are taken to get very large drops. 



It is pointed out that nothing can depend on the absolute 

 value of ^/p, since it has the dimensions of the product of a 

 length and a velocity. The naturally comparable length in the 

 system is the size of the drop. It is shown that diminishing the 

 size of the drop has the same effect as increasing the value of 

 fi/p. The velocity of the drop is probably the comparable 

 velocity ; but this cannot be varied much without introducing 

 large disturbances. 



The more complicated problem of a drop of one liquid falling 

 into a vessel of a different liquid is treated briefly, and the 

 analogy of the diffusion of vortex-motion with the conduction of 

 heat is referred to ; ^u/p, in the present problem, corresponding 

 with the diffusivity in the conduction of heat. 



The breaking up and subdivision of the rings is shown to 

 depend on (i) motion in the column, which brings about irregu- 

 larities in the ring, when the vortex-motion has nearly or quite 

 died out ; {2) the difference of density of the liquids composing 

 the drop and the column, on account of which the parts of the 

 ring, in which most of the liquid is gathered, fall most quickly, 

 and give rise to rings in the same way as that in which the 

 original ring was formed. Strong evidence is adduced to show 

 that capillarity is not concerned in the subdivision. 



Instances in which a small surface tension exists are also 

 referred to, and figures of some curious cases are given. 



The paper closes with a section in which it is shown that a 

 connection exists between the depth to which a ring travels in the 

 column and the form of the drop at the moment of impact at 

 the surface of the column. 



January 14. — Abstract of a Paper " On the Action of Sunlight 

 on Micro-organisms, &c." By Arthur Downes, M.D. 



In previous memoirs (Proc. Roy. Scv., 1877-8-9), of which 

 preliminary notes appeared in Nature, Dr. Downes, with 

 the collaboration of Mr. T. Blunt, showed that sunlight was 

 fatal to Microsaprophytes by a process of hyper-oxidation thereby 

 induced. 



In this process the more refrangible rays were the most active. 

 In ^the course of the induction which led to this conclusion 

 two other facts of importance were elicited. The molecule of 

 oxalic acid was speedily resolved into water and carbonic acid 

 by the combined effect of light and free oxygen, and a typical 

 representative of the diastases, the invertive ferment of cane- 

 sugar, had its qualities completely destroyed by sunlight, which 

 was, however, without effect in a vacuum or a neutral atmo- 

 sphere. 



During the past eight years evidence confirmatory of these 

 conclusions has accumulated from various sources, and the 

 principal facts are reviewed by the .author. 



After referring to the observations of Warington and others on 

 the nitrifying ferment, of Tyndall in regard to the insolation of 

 puttiefiable infusions under an Alpine sun, and to others. Dr. 

 Downes summarises the recent results of Duclaux, who finds, 

 from an examination of several species, that Micrococci are ap- 

 parently far more sensitive to sunlight than the more resistant 

 spore-forming Bacilli. Duclaux, who has likewise observed the 

 destructive effect of sunlight on a diastase, agrees that this 

 injurious action on germs is an affair of oxidation. In his pre- 

 vious papers the author had noted the different powers of 

 resistance of various organisms to sunlight, notably of Saccharo- 

 mycctes or A/iiccdiiies, as compared with Bac.'eria. He now de- 

 scribes a specially resistant Bacterium, roughly resembling, but 

 not identical with, the Ascobacterium of van Tieghem, of which 

 he finds no previous record. 



In refuting the conclusion of Jamieson, an Australian ob- 

 server, that both he and Prof. Tyndall had mistaken effects of 

 heat for effects of radiant energy distinct from heat. Dr. Downes 

 describes recent experiments of his own, which indicate that a 

 similar action, though of course in a less degree, is exercised 

 by diffused light. He concludes with a reference to the well- 

 known observations of Pringsheim on the destruction of 

 vegetable protoplasm by the more refrangible rays, and claims 

 them as evidence of the truth of his former generalisation that 

 the hyperoxidation of protoplasm by light is a general law from 

 the action of which living organisms require to be shielded by a 

 variety of protective developments of cell-wall, aggregation of 

 tissue or colouring matter, and in other ways. 



January 21. — "On the Clark Cell as a Standard of Electro- 

 motive Force." By Lord Rayleigh, M.A., D.C.L., Sec.R.S. 



This paper, supplementary to that " On the Electrochemical 

 Equivalent of Silver, and on the Absolute Electromotive Force 

 of Clark Cells" {Phil. Trans., p.irt 2, 18S4), gives the further 

 history of the cells there spoken of, and discusses the relative 

 advantages of various modes of preparation. The greatest errors 

 arise from the liquid failing to be saturated with zinc sulphate, 

 in which case the electromotive force is too high. The opposite 

 error of .(/(/(^-saturation is met with in certain cases, especially 

 when the cells have been heated during or after charging. Ex- 

 periments are detailed describing how cells originally super- 

 saturated have been corrected, and how in others the electro- 

 motive force has been reduced by the occurrence of supersatura- 

 tion consequent on heating. If these errors be avoided, as may 

 easily be done ; if the mercury be pure (preferably distilled in 

 vacuo) ; and if either the paste be originally neutralised (with 

 zinc carbonate), or a few weeks be allowed to elapse (during 

 which the solution is supposed to neutralise itself), the electro- 

 motive force appears to be trustworthy to i/iooo part. This 

 conclusion is founded upon the comparison of a large number of 

 cells prepared by the author and by other physicists, including 

 Dr. Alder Wright, Mr. M. Evans, Dr. Fleming, Prof. Forbes, 

 and Mr. Threlfall. 



As regards temperature coefficient, no important variation has 

 been discovered in saturated cells, whether prepared by the 

 author or by others. In all cases we may take with abundant 

 accuracy for ordinary applications — 



E = I -435 (i - 0-00077 (' - 15°)}. 



the temperature being reckoned in Centigrade degrees. For 

 purposes of great delicacy it is advisable to protect the standards 

 from large fluctuations of temperature. Under favourable cir- 

 cumstances two cells will retain their relative values to l/lo,ooo 

 for weeks or months together. 



Unless carefully sealed up, the cells lose liquid by exudation 

 and evaporation, and then the electromotive force gradually 

 falls. Marine glue appears to afford a better protection than 

 paraffin-wax, and there seems to be no reason why cells thus 

 secured should not remain in good order for several years. 



In cells of the H-construction (§ 29 of former paper), the leg 

 containing the amalgam (but not the one containing pure mer- 

 cury) is liable to burst, apparently in consequence of a tendency 

 to alloy with the platinum. Protection with cement of the pait 

 of the platinum next the glass has been tried, but no decisive 

 judgment as to the adequacy of this plan can as yet be given. 



Recent cells, intended for solid zincs, have been made of a 

 simplified pattern — nothing more, in fact, than a small tube 

 with a platinum wire sealed through its closed end. The zincs 

 are not re-cast, and the paste is prepared from (unwashed) 

 mercurous sulphate rubbed up in a mortar with saturated solu- 



