June 30, 1910] 



NATURE 



\2\ 



LETTERS TO THE EDITOR. 



\The Editor does not hold himself responsible for opinions 



expressed by his correspondents. Neither can he undertake 



to return, or to correspond with the writers of, rejected 



"inuscripts intended for this or any other part 0/ Nature. 



notice is taken of anonymous communications.] 



The Descent of a Sphere in a Viscous Liquid. 



KEs's formula fcr the terminal velocity of a sphere 



nding in a viscous liquid under the action of gravity 



■een recently tested by Prof. John Zeleny and Mr. 



V. Keehan (*' British Association Report," 1909, p. 



and they found that the values of the velocit\- fur- 



1 by it were considerably larger than those which 



obtained from their experiments. Since Stokes's 



Li!a is obtained on the hypothesis of no slipping, it 



un.ishes an inferior limit to the velocity, and consequently 



he discrepancy between theory and observation cannot be 



explained on any hypothesis that slipping takes place. 



I think that a possible explanation is the following, 

 rhe equation determining the current function contains 

 he term d^f'dt, the origin being some fixed point in the 

 ine of motion of the sphere ; and if the motion be referred 

 o the centre of the sphere as a moving origin, d^jdt must 

 lOt be put equal to zero when the motion is stead}-, but 

 nust be replaced by Yd^jdz, where V is the constant 

 •elocity of the sphere. The retention of this term creates 

 10 difficulty so far as the integration of the differential 

 quation for ^ is concerned, but the solution is quite 

 lifferent from that given by Stokes. 



A. B. Basset. 

 Fledborough Hall, Holyport, Berks, June 20. 



Popular Biological Misconceptions. 



The object of science is to increase the knowledge of 

 aankind in general, and not merely that of the workers 

 n science. The methods of science may be only under- 

 tood by the workers in each particular branch, but the 



R elusions are for all, and should be made accessible to 

 ■ The methods by which Newton established the law of 

 vitation can only be understood by good mathematicians, 

 lat the results can be put into words that can be under- 

 tood by any educated man. I think most will agree that 

 tudents of science should, so far as possible, make known 

 heir discoveries in such a way as to be understood by the 

 ayman. 



^ In making these remarks I have biology in mind. 

 MOthing is known of biology outside the ranks of biologists, 

 iven Darwin's theory of evolution is most imperfectly 

 raderstood^ by the ordinarily educated man. Probably 

 vorking biologists have no idea how much it is misunder- 

 tood. When the late Lord Salisbury at Oxford said that 

 here was nothing except pure chance to ensure the trans- 

 nission of an advantageous variation, he left out of con- 

 ideration the survival of the fittest, an integral part of 

 he theory. Sir Oliver Lodge, in " Man and the Universe " 

 P- 38), speaking of thej)ersistence of favourable variations, 

 2ys, " given ^ their appearance, their development by 

 ^"ggle, inheritance, and survival can be explained ; but 

 hat they arose spontaneously, by random change, with- 

 >ut a purpose, is an assertion that cannot be justified." 

 iTiis passage shows that the writer has not fully 

 Jrasped the elements of the theory ; the changes take 

 'lace in every direction, but all variations except those 

 n favourable directions are wiped out in the struggle for 

 wstence; such, at any rate, is the theory. When we 

 onsider that Darwin's theories are not fully grasped by 

 cholars, it is hardly to be wondered at that the ordinarily 

 4ucated man has but the vaguest ideas of biology, ideas 

 nade still more vague by the ordinarily educated writers 

 n the daily, weekly, and monthly Press. To the ordinary 

 nan the word Darwinism means the theory that his 

 mcestors were monkeys ; he will have heard the words 

 survival of the fittest " used as a catch phrase, but he 

 |]3ve no idea of their meaning: "struggle for exist- 

 nce " will have no biological sense for him; " selection " 

 •e will think has something to do with sex. Biologists 

 nay say either that I am exaggerating or that the 

 oucated men of my acquaintance must be singularly few : 

 ut I can assure them that such misconceptions are shared 



NO. 2122, VOL. S3] 



by very many men who have been educated at our public 

 schools and universities, which is generally (though perhaps 

 erroneously) considered the criterion of a good education. 

 It is quite common to come across persons who say that 

 Darwinism is discredited by new discoveries, especially by 

 Mendelism ; they have no other idea of the meaning of 

 Mendelism, and, seeing that their notion of Darwinism 

 is no more than I have stated above, they arrive at con- 

 clusions that would rather astonish the average biologist. 



I think it is the duty of biologists to educate the un- 

 educated in biological matters, to tell them how matters 

 really stand, and to tell them how far old theories are, or 

 are not, modified by new views ; but we should be educated 

 by first-class masters, and not by second-hand popular 

 writers. This has been done for a long time for astro- 

 nomy, and, to a certain extent, for physics ; it is very 

 desirable that it should be done also for biologv. ' 



C. C. 



Anomalous Reading of Hygrome'er. 



On June u I observed a case of the wet-bulb thermo- 

 meter reading higher than the dry bulb, which cannot be 

 attributed to a falling temperature, as this anomalous 

 condition continued for more than two hours, during the 

 greater part of which the temperature was slowly rising. 

 A gradually dispersing fog prevailed at the time, and the 

 dry bulb was at first covered with precipitated moisture, 

 but after being wiped dry it continued to read lower than 

 the wet bulb, without any further visible deposition of 

 moisture. This, however, may only imply that evaporation 

 was proceeding too rapidly to allow of the fog particles 

 aggregating into visible drops. This evaporation might 

 account for the temperature of the dry bulb being as low as 

 that of the wet bulb, but not lower. As thermal equilibrium 

 will be attained by each thermometer when its rate of heat- 

 loss is equal to its rate of heat-gain, and as the only loss 

 of heat is by evaporation, which at most can only lower 

 the dry-bulb reading to that of the wet, it is necessary 

 to suppose that the wet bulb absorbs heat more rapidly 

 than the dry. This may be accounted for by the greater 

 thermal diffusivity of the wet bulb with its saturated muslin 

 covering. 



Experiments made by Prof. A. W. Porter at University 

 College, London, show clearly that, in the case of steam 

 pipes of small diameter, the effect of a lagging of badly 

 conducting material is to promote the transference of heat 

 from the interior to the exterior, and it is evident that if 

 the external temperature be higher than the internal, the 

 effect will be reversed, and, further, that it will be in- 

 creased if the covering is not a bad conductor. We have 

 such a covering on the wet-bulb thermometer, and as 

 owing to evaporation the temperature of the thermometers 

 will be lower than that of their surroundings, the direction 

 of heat transfer will be inwards, and its rate more rapid 

 in the " lagged '' wet bulb than In the bare dry bulb. We 

 should accordingly expect the former to come to a state of 

 thermal equilibrium at a higher temperature than the 

 latter. J. Rowland. 



St. Beuno's College, St. Asaph, June 20. 



Pwdre Ser. 



Doubtless many of your readers will suggest that 

 Pwdre Ser may, in some cases at least, be the jelly-like 

 Plasmodium of Spumaria alba, D.C., a common British 

 m>-xomycete. The size, colour, time, and places where 

 found agree well with Prof. McKenny Hughes's descrip- 

 tion, but how it should be connected with meteors this 

 identification, if correct, would in no way explain. 



Agnes Fry. 



Failand House, Failand, near Bristol. 



The article on " Pwdre Ser " in your issue of June 23 

 has brought to my remembrance a tale of a shooting 

 star which fell upon a connection of mine many j'ears ago. 

 The man was working in the field, when a rnass of jelly 

 fell upon him. I discredited the story at the time ; but 

 this article seems to lend weight to the ston,-. I believe 

 the man was unhurt. The occurrence happened in Wales. 



Rowland A. Earp. 



Preston Brook, near Warrington, June 27. 



