104 



KNOWLEDGE. 



March. UHl. 



13. THE FINDING (.)1' THi: TIME .\T NIGHT.— 

 In the note by K. H. M. K. in the January number, in the 

 diagram of the dial a IV was misprinted for \'l. and for the 

 benefit of our readers who may be wishful to use it we insert 

 an amended illustration. 



14. WHICH IS FASTEST— SIGHT OR HEARING?— 



This (luestion is somewhat indefinite. In any practical case 



c.i>., the sight and sound of an electric spark, the relative 



\elocities of light and sound make it certain that the retina 



will be aftected earlier than the ear drum, but it does not 



necessarily follow that the consciousness of the light will 



precede that of the sound, though it will certainly be so if the 



spark is distant by more than a very few inches. If the 



question is which can produce the quickest physical response, 



it is practical and interesting, and can be made the subject of 



experiment : in this case, the relative intensities of the light and 



the sound are an important factor, and results with different 



indi\ iduals varv considerablv. , ,, ,~ 



J. H. (j. 



22. RADIUM. — The ratio given on page 4'! of Railinni to 

 Uranium should read 3->S x 10~'. 



2.T. THli TIDES. — Mr. Hardcastle in a reply to a <iiiei\' 

 of mine has, unaxoidably. as I quite see, from the wording of 

 the question, misapprehended uiy object. The question was 

 suggested by the pages in Darwin's "' Tides," pages 240-242, 

 to which he refers me. and I purposely did not mention 

 Darwin or carry the question a stage further ou, because I 

 wanted to elicit an independent answer and, if possible, one 

 independent of the mathematical fictiou of considering free 

 wave and forced wave motions in a single wave as separate 

 entities. A word about this "' fiction "' later. 



Adopting this fiction, it seems to me that a mental picture 

 of the way in which friction comes in and its direction, is much 

 more easily formed (the free wave tendency being continuously 

 destroyed by the friction) tlian if the wave forui is considered 

 as simply due at each moment to the combined action of lunar 

 force and gravity together. Now I imagine that Darwin 

 deliberately elected to avoid the fiction as possibly liable to 

 produce misconceptions in anyone new to the subject and 

 probably without mathematical knowledge. With the attempt 

 I feel every sympathy, but it creates, I think, more difficulties 

 than it avoids. There seeiu to me points in his presentment 

 of the subject which to a novice will appear shadowy or even 

 false. Moreover, I am doubtful whether he has really avoided 

 the fiction, and he has uiade his argument more difficult to 

 follow by unconsciously omitting a step (or half-step; the 

 principle has been explained earlier). At one point a 

 student will almost invariably ask, "How can a change in 

 the depth of the ocean suddenly reverse the action of the 

 friction?" and I think the answer would implicitly involve 

 the use of the tabooed fiction. To take only one point, 

 which point, however, forms the basis of the whole 

 argument, on page 241. " When, as in reality, the 

 lit|uid is subject to friction, it gets belated in its rhythmical 

 rise and fall, and the protuberance is carried onwards by the 

 rotation of the planet beyond its proper place." Now the 

 reader will very likely argue that friction would cause moving 

 particles to come to rest sooner, and therefore the rise and 

 f.ill would be accelerated, and the tidal prominence would fall 

 behind instead of in front of the moon, and I certainly think 

 that failure to see furtlier into the matter would not indicate 

 want of intelligence. Perhaps this may seem hypercritical, 

 and it is impossible to detune strictly what constitutes a 

 /)o/i;(/<n- explanation ; in general terms I should define it as 

 one which gave the reader a clear mental picture of what was 

 going on, without suppressing difficulties in the principles 

 applied. With regard to the latter point I need not say about 

 a book so widely known, how singularly free in general it is 

 from this weakness, and perhaps this is the only case 

 (probably the most difficult of those set for explanation), 

 where I should feel inclined to criticise the trcatuient as not 

 (|uite satisfactory. 



With reg.ud to the "fiction." it is in reality no greater 

 than that of identifying a force with two components into 

 which it may be resolved, .and is in fact, under more complex 

 conditions, identical with it ; but I certainly think that a 

 student beginning the study of dynamics should be eucouraged 

 to regard the kinematical parallelogram law, when applied to 

 dyuamical problems, in the light of an hypothesis, to be 

 N'erified by finding that in e\ery sort of combination it leads 

 to consistent results and is alwavs confirmed b\- experiment. 



J. H. G. 



THE ANCE.STRV ()!■ JJIJAIESTIC CATTLE. 



At a meeting of the Zoiilogical Society of London, held on 

 February 7th, Professor J. Cossar Ewart. F.R.S., gave an 

 account of some skulls of oxen from the Roman station at 

 Newstead, Melrose. The evidence which he had obtained 

 was against the descent of all European cattle from the Urus 

 i/ios priiiiigcnius) as well as of that of all European, Indian, 

 and African breeds from the Asiatic Urus (B. iiomadiciis). 

 His conclusions are as follows: — 



1. That the Celtic Shorthorn (Bos loiii^ifroiis) is probably 

 more intimately related to the Zebu of India (Bo.s 

 iiidicKs) than t(.) the European Urus iBos /)/•/;;; /,i;c;n//i- 1. 



That long premaxillae are usually correlated with an 

 occiput of the Bos priinigeinus type, while short 

 premaxillae are usually correlated with an occiput of 

 the Bos aaitifrons type. 



That polled black Gallowa\' cattle and polled white 

 "wild" Cadzow cattle are intimately related to the 

 Urus, that flat-polled Aberdeen-Angus cattle probably 

 include amongst their ancestors an ancient Oriental 

 race now represented by, amongst others, a Syrian 

 breed with rudimentary horns, and that round-polled 

 cattle may belong to a still more ancient Oriental race 

 descended from Bos aciitifrons of the Punjab Siwaliks. 



