Sept. 5, 1884.] 



♦ KNOWLEDGE ♦ 



207 



•• 1, Bedford-square, W.C, May 14, 1884. 



" My deak Dk. Kinns, — Having gone over the proof-sheets of 

 the Seventh Edition of your book, ' Moses and Geology ' — or, 

 rather, tliat portion of it devoted to the subject with which I am 

 more familiar, the brain and its wondrous nervous connections — X 

 may say jour descriptive matter is all that I can desire it to be, 

 lending a charm and a value to the generally instructive character 

 of your work. — Btlieve me to remain, yours very sincerely,— Jabez 

 Hogg, M.K.C.S., Consulting Surgeon to the Royal Westminster 

 Ophthalmic Hospital ; Fellow of the Medical Society, London, &c." 

 " 97, Highbury New Park, May 15, 1884. 



" My dear Dr. Kixns, — I have at your request again examined 

 all the Hebrew references in your valuable book, ' Moses and 

 Geology,' and find them quite correct. I humbly believe that you 

 have done immense good by proving the correctness and authenticity 

 of the sacred records, and trusting you will meet with that snccess 

 which your ardour and pious labour truly deserve, I am, my dear 

 doctor, yours very sincerely, B. H. Ascheb, Rabbi of the United 

 Synagogue." 



THE BEST FORM OF TRICYCLE. 



[1386] — During my tour along the south coast I saw Kxow- 

 LtDGE, and noticed an article on tricycles. I ride a 36-in. 

 " Merlin," and find it most suitable for my own use; but, having 

 formerly ridden a Coventry " Compressus," I thought how near 

 youi ideal machine it approaches. Having often ridden with the 

 " Compressus," I know there are few machines that surpass it, 

 only that it requires the rider to get a little forward to get additional 

 weight on the driving-wheel going up hill ; and for those who care 

 to have two speeds it can easily be applied. But it mainly dismisses 

 the great point of Large v. Small Wheels, inasmuch as the large 

 wheels carry the weight at level running, while the small one does 

 the driving. 



I think if you would give the machine in question a little study 

 and fair trial, you will be disposed to pronounce it second to none 

 of chain-driven tricycles. 



Have vou tried the new " Merlin," and what is vour opinion of 

 it y ' " H. A. 



MIXD AXD BRAIN. 



[1387] — If not encroaching too much on your valuable space, in 

 reply to your editorial note on Huschke's dictum, that the vibra- 

 t;ions of ether do not become colour until they are transmitted to 

 the brain." I would rather put it thus: — "The phenomenon of 

 colour is perceived " by the brain, through the eye and connecting 

 nerves, and there transformed into the idea or thought expression 

 — viz., colour. Nevertheless, the phenomenon of colour would still 

 exist or be formed in fact, whether we could see it or not, or 

 whether we called it colour or any other name. So I take Buschke 

 to mean that the vibrations of stimuli, transmitted from within or 

 without to the brain, are there transformed into thoughts or ideas 

 by the self-acting molecules of the brain, whatever names we may 

 give them. 



In short, like the vibrations of light are transformed — say by a 

 prism into colours — so are the "vibrations of stimuli passing through 

 our nerves and the brain transformed or modified into thoughts or 

 ideas. F. W. H. 



[Just so. External stimuli may be " transformed into" thought 

 by the molecular vibration of the brain ; but the contention of 

 Biichner and Uuschke is that such vibrations are thought, which to 

 ordinary minds is simply inconceivable. — Ep.] 



THE TERMS 



PRIMARIES" AND "SECONDARIES 

 APPLIED TO COLOURS. 



AS 



[1388] — In a recent issue of Knowledge there was some refer- 

 ence to what have been — under the nomenclature founded on 

 erroneous conceptions regarding colour — termed primaries and 

 secondaries^ or complementaries. Colours are still regarded, and 

 spoken of, as if they had external existence. Persons, even those 

 esteeming themselves " scientific," have constantly to be reminded 

 that colours are but sensations, or appearances, excited in us by 

 vibrations of different periodicities. Externally to sense the 

 vibrations which excite all the different sensations of light (colour) 

 in us are simply vibrations without luminosity or colour. " The 

 light is within us." Now, we cannot consistently speak of primary 

 and secondary sensations. The complementary colours, as they are 

 <;alled, are not the effects of mixed sensations, but of the combined 

 action of different wave lengths. It matters not whether vibrations 

 be produced by the prismatic spectrum or by pigments, it is by 

 means of vibrations alone that vision is effected. Let, for the sake 

 of argument, the wave length of red be represented by 14, and blue 

 liyO; then, if the two vibrations simultaneouslv aSect the same 



portion of the retina, we shall experience a third sensation of 

 colour — the result of their combined action. Correctly speaking, 

 it is not a colour that has a complementary, but a vibration. 



In my little work upon *' Light" I have expounded the principle 

 of complementary vibrations — a principle which the late Mr. 

 William Spottiswoode pronounced to be a sufficient and complete 

 explanation of the phenomena. But to our point, the prism does 

 not refract colours, but vibrations ; externally to the eye, there is, 

 therefore, nothing but differentiated vibratory action, and by this 

 medium all our varied sensations of sight are affected. On a 

 future occasion, if permitted, I will advance reasons why it is also 

 inconsistent that the terms primaries and secondaries should be 

 applied to differentiated vibratory action. W. Cave TaoMAS. 



[Carrying out the principle enunciated in the above letter in its 

 integrity, I have no business to talk about the object on which X 

 am writing as " a table." What — if I rightly apprehend Mr. Cave 

 Thomas — I ought to say is that I have certain sensations which I 

 call brownness, blackness, hardness, resistances, extension, the 

 scent of Morocco leather, &c., the sum of which make up my 

 concept. I have myself said (in a note to letter 1362, p. 144) that 

 the ethereal vibrations do not become colour untU they have been 

 transmitted through the eye and optic nerve to the brain ; but, 

 alike for the purposes of science and common sense, we treat 

 colours as objective realities. — Ed.] 



LETTERS RECEIVED AND SHORT ANSWERS. 



The Honorary Secretary of the Cork Literary and Scientifr- 

 Society is requested kindly to read the paragraph which concludes 

 the first column on p. 62, and which has recently appeared on other 

 occasions in this journal. — E. P. The whole thing is a matter of 

 common sense. Mechanical pressure is admittedly a — or rather the 

 — vera cau^a of such a movement, and Faraday's contention was 

 that pressure was innocently exerted by the operators. His 

 apparatus was so constructed that when pressure was applied the 

 index moved, and when such pressure ceased to be applied it 

 remained stationary. With the result you are familiar. Hermann, 

 the conjuror, brings two live rabbits down into the stalls, and, 

 holding them up by the ears in the very midst of his audience, 

 strokes them into one. On the principle of Par^nmonia principionim , 

 I find a ready explanation of this in the conjurer's proficiency in 

 sleight-of-hand. Suppose, though, that some one chose to assert 

 that the spirit of (say) Hermann's deceased wife's sister had removed 

 the second rabbit, or incorporated it with the first, and that you or 

 I were to suggest a plan (such as catching the performer by the 

 wrist at a pai'ticular stage of the trick) by which the disappearance 

 of rabbit No. 2 was prevented. Are we to be told that because the 

 performer failed to unite the rabbits, our device " leaves the 

 question just where it was ? Without the postulate of Parsimony 

 it is migatory, and with that postulate it is superfluous ? " — 

 Sidney Woodforde. For the dozenth time I have nothing to add 

 to what I wrote on p. 58 of Vol. V. of Knowleikje. I really must 

 beg you (and scores of correspondents who persist in sending me 

 stamped and directed envelopes for private replies) to read, mark, 

 learn, and inwardly digest the sentence in capital letters which 

 concludes the heading of the correspondence columns. — L. G. R. 

 See answer to E. P. above. — C. H. Johns. You will find the Unes 

 you quote in Wordsworth's "Tintern Abbey." — The Secretary of 

 the Bow AND BROMtEY INSTITUTE is requested to be good enough to 

 read the first reply above. — W. W. S. The " Monthly Notices " of 

 the Royal Astronomical Society are published by Williams & 

 Norgate, London. 1 do not know the price to the public. All 

 information with regard to the publications of the Liverpool Astro- 

 nomical Society may be obtained on application to W. H . Da vies, 

 Esq., F.R.A.S., 55, Great Newton-street, Liverpool. — Anontmocs 

 (Sunderland). Our advertising columns are open to you. — John 

 Hampden. Some one has been hoaxing you. Does not your own 

 common sense suflSce to show you that, were the earth flat, no 

 intermediate stations whatever would be needed between Wimble- 

 don and Portsmouth ? — SiGSLA. It appears as though you were 

 incapable of realising the meaning of Infinity. How can yon pos- 

 sibly add — or subtract — from Infinity, or one infinite quantity from 

 another ; or conceive a circle vrith an " infinite " radius ? As for 

 your notions of equating two expressions each of them = nothing; 

 a very old mathematical joke will serve to illustrate where that will 

 land you. Let a = T> : then a'' = ab and a'- — b- = ah — h- : or {a + i) 

 (a — b) = {a — h)b or a + b = b : i.e. 2a = a or 2 = 11 — C. Frederick 

 Wilkinson. — Thanks for your interesting extract, which is marked 

 for insertion. — Chas. Aldridge. The Editor is nearer to you than 

 you imagine. Tonr letter will be forwarded. — Erimus. Does " every 

 ninth wave rush in .vith greater volume and force than any of the 

 others ? " — Dr J. Murray Mooee. How could a star which appeared 

 in Virgo, by any conceivable possibility, reappear in Cassiopeia ? 

 A new star did blaze out in Cassiopeia from Nov., 1572, to March, 



