May 19, 1882.] 



KNOWLEDGE 



611 



next stake being £4, you lose, and enter in both losing columns. 

 Yon next stake (1 + 2) 6, and win. Proceed as before, and stake 

 3 ; if Tou win, your scheme will have completed, as it were, one 

 revolution, as ail the nju^es in the centre column are crossed out ; 

 and your winnings are £20, against £13 lost, leaving you £7 to 

 windward, as sailors say. If you lose, you must go on staking as 

 before, until the tigures in the centre column are crossed out, when 

 yon will be the winner of £7. in exery case !' 



It is obvious that instead of 7, any niimher may be used, and 

 may be divided into the greatest possible number of whole parts. 



INTELLIGENCE IN ANIMALS— JUMBO. 



[402] — As another jiroof that we are not the monopolists of intel- 

 ligence in the animal world, it is reported from America that just 

 before Jumbo reached the truck in which he was to be confined, 

 some planks, two or three feet high, had to be crossed. Uefore 

 proceeding, however, he thumped them hard with his trunk, and 

 then pressed them with his fore feet. Why should this reasoning 

 in a brute be called instinct, when with us it would bo called 

 common-sense ? H'sett. 



THE LUMINOUS MIXTURE OF BLUE AND YELLOW. 



[403] — Professor Rood's observation is not silly, as Colonel Ross 

 states, but incorrect — a fundamental error made by Brewster. 



Colour is a sensation bearing no resemblance to its physical cause. 

 To mix colours is merely to excito simultaneously the same parts of 

 the retina with the stimuli, which are known by experience to 

 excite severally the sensations of colour it is desired to combine. 

 Lambert's method obviously accomplishes this object. Other 

 methods are : by rotation on the colour top ; by simultaneoos 

 illumination of a white object, as with the double magic-lantern. 

 Moreover, elaborate apparatuses have been devised for the luminous 

 mixture of the pure rays of the .spectrum. AH these methods lead 

 to the same results, which arc accepted by all who have studied the 

 subject, and are really as well established as any scientific facts. 



To explain Colonel Ross' results would require a special investiga- 

 tion of the circumstances of each case. I would remind liim, how- 

 over, that, in order that blue and yellow may combine to form white, 

 the blue must be exact in hue ; the slightest leaning towards green 

 will impart a green tinge to the result, which, in the Hamo method, 

 may seem very conspicuous. 



In regard to the last experiment — 



(1.) The explanation cannot be true. The idea that the mere 

 concentration of the beam can affect its refrangibility is quite con- 

 trary to what we know of physical optics. 



(2.) If it were true, it would not prove the point. It would prove 

 only that the complementary colour of a red formed from the 

 extreme rod rays is green, as indeed it is. If, however. Colonel Ross 

 insists on the grass green, I think he is at issue with accepted facts 

 on another point. John Tenxant. 



DOES THE MIXTURE OF BLUE AND YELLOW MAKE 

 GREEN light:- FLUORESCENCE. 



[40t] — Letter 388, in Kxowiedge, for April 28, proves what 

 difficulty is caused (in treating of colours) from the want of definite 

 names and an invariable standard of reference. Lieut. -Col. Ross 

 shows that by common usage, the term " blue " is applied to the 

 chloride of copper flame ; and the same might be said of the Bunsen 

 flame. In the same way Newton gave that name to the colour 

 which follows green in the spectrum, and called the deeper bine, 

 which comes next, " indigo," and the still deeper and darker blue, 

 which closes the series, " violet." Y'et Newton's indigo, which is 

 exactly the hue of artificial ultramarine (or French blue), is really 

 a purer blue, differing from his other blue in containing less mixture 

 of green ; and Newton's violet, which is commonly supposed to 

 have a tinge of red, and which some even term "'purple,'' has been 

 proved by most acctirate observations (when viewed by itself) to be 

 absolutely free from red, and from any appreciable quantity of 

 green. ^Vhen the flames above referred to are viewed through the 

 prism, it is seen that they give out a large quantity cf green light 

 as well as of pure blue. When the blue part is neutralised by the 

 addition of a yellow light, as in the experiments referred to in 

 Lieut.-Col. Ross's first letter (p. 41)6), the greenness still remains, 

 and appears in the resulting colour diluted with white. 



The following most beautiful and instructive experiment, how- 

 ever, settles at once and for ever what is the colour which, when 

 added to yellow, makes white ; and it teaches far more than any 

 experiments with coloured flames or pigments can teach. Lay two 

 rectangular pieces of white paper so as to touch cornerwise over a 



• This is exclusive of what you gained before you began to lose. 



dark cavity, the edges of the touching comers being in the same 

 two cross lines, and in the same plane. Then view through u prism, 

 held parallel to one of the cross lines, the spectra of the two white 

 spaces. On one side we have the series of colours — red, orange, 

 yellow — formed by combinations of the prismatic rays beginning at 

 the red end of the spectrum ; on the other side, tho series formed 

 by the rays wanting in the Urst^sea-green, sea-green-blue, and blue 

 (the best and purest blue that ever tho eye can behold). And in 

 those two series the opposite colours must be perfect complemen- 

 tnries — the sea-green to the rod, the sea-green-blue to tho orauge, 

 the blue to the yellow, as may be seen by causing one piece of paper 

 to slip forward so as to pass tho corner of the other piece, when the 

 overlapping colours all turn to white. 



It is ea.«y, therefore, to see that when we inquire whether 

 mingled blue and yellow lights make white or green, we must dis- 

 tintruisli between the different colours which are commonly called 

 blue. As to the binary compound of green and blue, tho comple- 

 mentary- of red (which is exactly the hue of fresh verdigris 

 powder), it is unfortunate that we have no good distinctive name 

 for it. I have not met with a better term than "sea-green"; 

 which term is certainly not derived from the appearance of yellow 

 sand seen through green sea-water, but is the colour of a peculiar 

 reflection of the sky from tho sea — a tint hardly ever seen in 

 nature elsewhere, except in a few minerals, and sometimes in the 

 sky itself. 



i beg pardon for so hastily suggesting a mistake in the experi- 

 ment described by Lieut.-Col. Ross in his Fact 4. The green light 

 he saw in the prism, when tho focus of his lens was thrown upon 

 it, was no mistake, but is a beautiful, and to me quite new example 

 of the fluorescence so ably expounded by Professor Stokes in the 

 Phil. Trans, for 1852. Glass is known to partially obstruct the 

 invisible ultra-violet rays ; but I do not recollect seeing it noticed 

 before that this is attended with the'production of a green luminosity 

 in the glass. If the converging rays are made to fall on the flat 

 end of a prism, so that the focus is formed in its middle, the 

 luminosity may be seen extending from end to end of the prism, 

 accompaiiied with two parallel reflections, more easy to understand 

 than the reflections which complicate the experiment described on 

 p. 4f6. 



A very beautiful and bright sea-green-blue fluorescence is produced 

 when a sunbeam is made to converge to a focus in a weak infusion 

 of the bark of the ash or the horse-chestnut, or a weak solution of 

 quinine ; and in these cases the peculiar luminosity is strong enough 

 to be seen in the fluid when the sun shines upon it, without tho aid 

 of a lens to intensifv the incident light. W. Bensox. 



THE POTATO. 



[405]— In No. 24, p. 520, " F.C.S.," replies to my letter in 

 No. 20. He takes me for an English farmer. I have the pleasure 

 of informing him I come froa the North, and know both the prac- 

 tice and theory of my profession. I agree with "F.C.S." that 

 we get many hints from our Continental neighbours, but at the 

 same time deplore the fact that most members of "F.C.S.'s" 

 body think they know farming, whereas very few of them can talk 

 of farming matters without immediately saying something which 

 evcrv practical man knows to be nonsense, and when the practical 

 man sees him talk nonsense on what he knows about, he very 

 naturally concludes he also talks nonsense when he goes so deep 

 into the subject that he cannot follow him. 



With five experiments during 1870, 1880, 1881, cut and uncut 

 flowers were as near as possible identical, viz., 8 tons 15 cwt. per 

 imp. acre, on an average. 



What I meant about the frosted potatoes was this : take say two 

 samples of frozen potatoes from the same heap, cook one in the 

 oi-dinary way, by boiling ; roast tho other in hot wood ashes ; those 

 from the latter will be good food, the boiled ones too sweet to be 

 palatable, so that I say it is the frost coming out which makes the 

 change, not going in. 



I have tried many times most manures, pure, single, and com- 

 pound on many crops, both on sand and clay. I see "F.C.S.'s" 

 experience is second-hand, although not much the worse of that. 



.\mong most agricultural experimenters, it is generally acknow- 

 ledged that the presence of a large quantity of decomjiosing organic 

 matter increases not only the crop, but also the percentage of 

 disease. Now, " F.C.S.'s " experiment being on sand, there was 

 likely to be little organic matter present, or if so, it was not a suit- 

 able station, and had it been on moss, the percentage of disease 

 woold also have been small ; therefore I cannot see but that there 

 is a contradiction in saying that where we have organic matter, 

 and. of course, expect a large crop, that there we have most disease, 

 and again in the unmannred plot with no organic matter and a 

 small crop, that it is also the worst with disease. At least such I 

 take to be his meaning. 



