Mat S, 1SS5.] 



♦ KNOWLEDGE ♦ 



401 



demonstration, while the beharioar of the raJJy glow waa directly 

 contradictory to it. 



1 tliereforo await another opportunity of further observation in 

 order to confirm or refute ray present supposition, viz., that both 

 sources of illumination operate and are superposed, but the ruddy, 

 copper-like glow is only seen when and where the atmosphere is 

 permeable by obscure heat rays. \V. llAiriKii \Villi.\ms. 



EFFECT OP COLOIIE UPON TEMPERAMENT. 



[16V>S] — The Sanitary Record states that puppies have been 

 brought np under coloured glass, with the result that under red 

 pugnacity was deficient ; under blue temper was bad; but under 

 green the subjects were lively, cheerful, graceful, playful, and good- 

 tempered. The Pall Mall Qazcttc remarks that these differences 

 are " in nowise such as the association of ideas would lead us to 

 expect." This is a mistake ; red is the coolest, blue the hottest 

 (save indigo and violet), and the nervous irritability would be in 

 proportion. Green being the juste milieu, might bo expected to 

 give the best results. There may be sense in the advice to have 

 all nurseries glazed green. Hallyaeds. 



THE EVOLUTION OF THE SENSE OF BEAUTY. 



[1699] — May I be permitted to correct an error in the instalment 

 of my article which appeared in your issue of April 21th ? I refer 

 to the following sentence :— " Sir John Lubbock finds that they 

 [bees] chiefly affect orange and yellow, and that they like blue 

 next best." This statement was made in my rough draft, when 1 

 was acquainted with only the earlier experiments of this dis- 

 tinguished observer, described in the " Journal of the Linnaan 

 Society," vol. xiii. (Zoology). The alteration which I afterwards 

 inserted — " Sir John Lubbock finds that they show a decided 

 preference for blue" — was unfortunately omitted in transcription ; 

 and, as I did not receive proofs, I was not able to make the cor- 

 rection. I may mention also the misprint; of " Englena " for 

 " Englena," and ''eclimi" for "echini." 



Co.NSTAXCE C. W. NaDKN. 



[1700] — In an article under the above heading in last week's 

 Knowledge, the writer states that " the first animal which developed 

 a dim colour perception would from the outset find pleasure in 

 exercising the new faculty." Will she kindly explain how this de- 

 velopment came about ? Is not this precisely what she proposes to 

 ascertain ? and yet the subsequent reasoning is based on this 

 statement. G. H. 



MATTER REQUIRING REFLECTION. 



[1701] — Berkeley's theory of the non-existerce of the universe, 

 except in some mind or minds, is puzzling. 



Here is another puzzle. In the room in which I am writing 

 there is a looking-glass over the mantelpiece, and on the mantel- 

 piece a clock. Now if I stand directly opposite the clock I see no 

 reflection of it in the glass, its image being hidden (so it is difficult 

 to help believing) by the clock itself. But if I move to the right I 

 see the reflection to the right of the clock ; if I move to the left I 

 see it on the left. The farther I move to the right or left the 

 nearer to the right or left edge of the glass moves the reflection. 

 If I stand in one position, and some one else in another, I see the 

 reflection on one part of the glass, he on a different part. 



Now suppose we both quit the room, leaving it empty of mind 

 and eyes, on which portion of the glass is the clock reflected, or is 

 it reflected at all in the absence of eyes to see the reflection ? 



__^ M. T. H. 



" FULL INSIDE." 



[1702]— "C. N." (1681) admits that something exists inde- 

 pendently of consciousness, which something, I assert, must by 

 invincible necessity be external. And if external, then by the 

 interactions of this something and my reasoning faculty tlirough 

 the media of sensations I am approximately made acquainted with 

 the mntual relativity that subsists between me, the subject, and 

 it, the object. I know, therefore, that this something, whilst 

 internally conceived, externally exists. It exists externally to me. 

 If it were not so, then could mind have no conception of it, since 

 sensation would be wanting, or, having conception, could have no 

 basis of certitude for the truth of its ideas. J. S. 



LETTERS RECEIVED AND SHORT ANSWERS. • 



Beknaro Thomas. — The centre of the circle, whereof any given 

 Rainbow forms an arc, is always situated 180^ from the Sun's place 

 in the celestial vault. Now, when the sun was 2h. 45nt. past the 

 meridian at Llandudno on April 25 ho must liavo been a very little 

 over 38° 2',)' above the horizon ; and henro the centre of your 

 rainbow arc must have been depressed by that amount below the 

 opposite point of it. But the radius of a rainbow is about 41', 

 hence the little piece only which you saw peeping above the horizon. 

 Of course, as the Sun's altitude deolinetl, Ibe itainbow would rise. 

 ■ — H.\iloLi) Tavlok suggests that the concluding sentence in the paper 

 on the Ruddy Eclipsed Moon (p. 34-2, col. I.) is not quite intel- 

 ligible. — Thkta. The sphere is supposetl to be divided into tw(?lvo 

 equal spherical pentagons, two of them polar; and an equidistant 

 projection of each of tho twelve overlapping spherical spaces 

 enclosed by the circles circumscribing these pentagons is given. — 

 I'.\tex-Ato.m(?). See Vol. V. of Kxowleugk, pp. 180 el 

 seq., for reply to your first question. With regard to your 

 second, — When it is New Moon to tho Earth it is Full Earth 

 to the Moon. Tho so-called " Old Moon is the New Moon's 

 arms," is simply the part of tho lunar disc upon which the sun lias 

 not yet risen, lit up by earth-shine. It is what is called " Irradia- 

 tion," which makes the sun-lit crescent of tho moon seem bigger 

 that than part visible only by the comparatively dim earth-light. — 

 East Wind. 1 have asked for information myself {ride p. 353). — 

 G. H. Knox's " Differential Calculus for lieginiiers," published by 

 MacMillan & Co., and reviewed on p. 5U, is first-rate. See, too, 

 the " Easy Lessons," by the conductor of this journal in our second 

 volume. I know of nothing equally simple tre.itiiig of the Integral 

 Calculus. — Sexex. Well, if you need a more striking illustration, take 

 an ephemeron and a raven born on the same day. — A Workinc Max 

 asks Mr. Mattieu AVilliams exactly how much bicarbonate of potash 

 should be added to, say, a quart of gooseberries to exactly neutralise 

 their acidity. He has been experimenting recently with the result 

 that the fruit "always effervesces with the acid .... and gives it 

 a funny taste." He also finds maltose "answer very well indeed 

 with bread, but not so well with oatmeal ; " but is not sure whether 

 he has the right kind of malt. The first he obtained was called 

 pale malt, but he afterwards got some " exactly like grouiid coffee." 

 He wishes to know which is the proper kind to use. — C. Arthur 

 Pearson. An oak, boxwood, or lignum vitic ball of an inch in 

 diameter would fall from the top of a tower 200 feet high in jire- 

 ci$ely the same time as a leaden one of tho same dimensions. A 

 feather ball of the same size would also fall in the same time, but 

 for tho resistance offered by the air. In vacuo, a feather and a 

 piece of platinum would reach the ground at the same identical 

 instant. See paragraph in capital letters concluding those which 

 head the Correspondence Column. — W. D. Johxsto.v. If gas existed 

 in space it must retard the passage of bodies through it. Try to 

 run when chest-high in water. Start on the engine of an express- 

 train on a calm day and travel at the rate of sixty miles an hour, 

 and feel the resistance of the air ; and then consider cosmical 

 velocities, and see how infallibly the gaseous contents of space 

 which you postulate must derange the motion of everything 

 traversing it. — A Sdescribee. I don't know. It is a question 

 having no reference to science. — A Cox.stant Reader of Kxowledgb 

 asks for Mr. Browning's advice anent a tricycle which he wishes to 

 ride vrith his wife. He is already a bicyclist ; and the lady wishes 

 to get a machine which she can either ride alone or with him. Is 

 a Sociable or a Tandem the best for all-round work ? If so, what 

 description of either sort ? — W. W. Vol. II. of the " Celestial 

 Cycle," by the late Admiral Smyth (the "Bedford Catalogue"). 

 Fomalhant is simply fom-al-hiit — the Arabic for "the fish's mouth," 

 the star being situated in the jaws of Piscis Austalis. Betelgeux, 

 Smyth derives from the Arabic ibt-al-jauza — the giant's arm-pit, or 

 shoulder — a Orionis being situated in that part of the conventional 

 figure of the great hunter. — Haphael Tuck & Soxs, C.Nottage. Re- 

 ceived with thanks. — R. E. C. Without troubling " F.R.A.S." in the 

 matter at all, it vpill suffice to saj" here that the size of the flat in a 

 Newtonian telescope should be sufficient to reflect all the raya 

 coming to it from the imago of the sun or moon at that portion of 

 the cone in which it is placed. Obviously the image of a star is a 

 point, and hence a smaller flat will reflect all the rays which reach 

 a given point in the tube from such a source ; though, equally 

 obviously, such a small flat would actually act as a stop, and cut 

 off part of the light proceeding from the luminary with a disc of 

 sensible angular magnitude. A plane made larger than this acts 

 as a stop in another way, by needlessly cutting off the parallel rays 

 en route to the large mirror. Hence the reason why, in practice, 

 the diagonal reflector slightly exceeds the size merely needful to 

 send on all the rays from a fixed star. Yotu- idea of bevelling its 

 edge is theoretically good, but would, of course, add to its cost. — 

 W. B. You are too funny — you are, really. — A. Neilsox. Glad to 



