202 



KNOWLEDGE 



[Auo. 18, 



linked by the f^rMt law of compensation, by the law of the equitable 

 ilistribation of force, wliirh may be thus stated, vir., that whatever 

 aberration'takes place in exeesa of a mean state must bo rectified 

 by un oqoal [?J and opposite one in defect, and vice i'«rsii, or wcll- 

 beinp would be imperilled. 



The fact that the sentient eye is the only " ooloor-bo!c," and 

 that ittemal to it there are but mechanical vibrations of different 

 periodicities, is not sufficiently present to men's minds to prevent 

 them from reasoning as if colour were a property of the vibrations 

 themselves. This has been the case with resjwct to the explanation 

 of the ocular t^iectra ; the phenomena have been regarded as external 

 effects, instead of internal, and due to the reactions of the nervous 

 system ; they are sequent sensations which may be |)erceived, 

 thouph the eye be closed against all external vibratory action. An 

 initial sensation of a black s(K>t in a white field is succeeded by one 

 of a white spot in a black field. A sensation of a dark colour in a 

 white field, by its light complementary sensation in a dark field, and 



We find, then, that the changes in the sense of colour which are 

 produced by the cooling of beads, and which were alluded to by 

 a correspondent in a recent number of Knowledge, also occur in the 

 retina by the reactions which take place after an initial sensation. 

 The complementary spectra arc entirely subjective phenomena. 

 After a very strong initial sensation of hght, the sequent spectra 

 endure for a sufficient length of time to enable anyone to experi- 

 ment with them. For instance, after being dozed by the sun, any 

 sequent spectrum, say dark green in a light Cold, will appear light 

 red in a dark field, and become dark green again in a light field, — 

 here, then, are instances of the vibratory reactions within the 



r\ uu; system producing different sensations of colour. 



W. Cave Thomas. 



HERNIA AND TRICYCLING. 

 olO] — Dr. B. W. Richardson is altogether mistaken about this. 

 I am fis years of age, and have had hernia on both sides for 30 years. 

 When 04 1 commenced to ride a tricycle, riding doily three miles to 

 business and three miles back, without the slightest inconvenience. 

 I ought to say that I wear a Cole's double truss. This time of the 

 year I enjoy three or four games of bowls every fine evening with 

 impunity. K. K. 



SIXGCLAR BAIXBOW. 

 ^517] — I do not know whether I am contributing anything to 

 Knowledge, but what I have to relate is quite new to me.. A 

 thunder-shower was a|iproaching us the other evening. A most 

 brilliant and perfect rainbow was formed with a secondary bow, 

 also very bright, but in addition, between the two wnj a third, in 

 the shape of an ellipse, with the colours in the same order as those 

 of the primary-, and touctiing tliis near the ground. It was not 

 sufficiently perfect for me to see whether it touched the secondary 

 bow, but I think that if it had been perfect it would have done so. 

 J. F. HoUNTnWAITE. 



HAIR TURNING GREY. 



[518] — My grandfather was surgeon of U.M.S. Ardent at the 

 battle of Copenhagen. One of his assistants (a young man who 

 had only just joined the service when the fleet sailed for the 

 Baltic) was so overpowered with fear that he cowered down 

 stupefied daring the whole of the engagement, and his hair, which 

 was dark, became white. I have frequently heard my father, him- 

 self a naval surgeon, refer to this case, and I believe it to bo strictly 

 true. J. Thomson. 



28 July, 1882. 



EFFECTS OF LIGHTNING. 

 [511)] — In a thunderstorm which 1 witnessed near Bcrryville, 

 Tirgioio, July, 1879, a wooden house with iron stove and pipe was 

 struck, and a woman killed. On examining the structure I found 

 three places where the wowlcn boards of the walls were smashed 

 outwards just at the level of the floor. Rough, jnggcd holes had 

 Ijecn pierced, the cnrrcnt, which entered by the stove-pipe, having 

 diTide<l, and left the house on three sides. One of the tracks could 

 bo traced to a well about six yards distant, down which the dis- 

 charge paucd. G. R. Winne. 



A POWEBFVL electric light on the steamer liotehvd created an 

 immense st^nsation among the Indians at Fort lierthold, in Dakota. 

 The light was tamed upon a group on the shore, when they wero 

 fiaralysed for a moment, and then they set np a dismal chant, lay 

 down and rolled, and were with difficulty pacified. They called it 

 the white man's big moon medicine. 



anstoris to CoiTfgpouljnitst* 



•«• All commumieationi /or tt« Editor requiring tarlg aUtnlion ihouIJ rtaelk Ihr 

 Offict OH or hifoTt lltt SulHrdnii prreeding Iht currfHl ittut (ff KnoWLBDOl, the 

 tHcrtariHg circulation t^f tchick compctf ut togoto pret* early in the vefk. 



Hlirrs TO CosusroxniiiTO.— 1. So queiliont aekina /or ecitnlifie in/ormation 

 can be amrered through the poll, i Letteri tent to the Editor /or corrnpondenle 

 camHut be/orvawdtd, nor can the namee or addreetee nf correepondentg be given i» 

 antrrr to primte inqiiirice. 3. Correipondenti lAoiiU ifn(» on one tide o»J» c/tlu 

 ]>aper, and put dravinge on a eepartite tei\f. 4. Each letter tkould have a title, and 

 %H reptj/ing to a Utter, r^erence ehould be made to He uvmler, the page on which it 

 appeart, and He title, 



Alleyne Reynold.!). Our paradox corner is not for paradoxes of 

 that sort. The one you quote naturally arises from the initial »= 

 x + 1. Wlicncc, you say, x = infinity j but, however largo x may be, 

 x+l-x is always unity. Squaring both sides leads to «• = »:• -I- 2.i; 

 + 1 i whence x= —i; but wero as infinite, you could no more cancel 

 the two terms «' hero than the two x's in the original equation. — 

 Paget Higgs. Quaternions would scarcely suit the majority of our 

 readers.^ — Uv. Bowman. Fear space will not permit. The influence 

 of moon on weather is a very prolific subject. I can, from my own 

 experience, affirm that no two believers have identical views. — H. 

 Nelson. Only experienced engravers could say whether a spec- 

 tacle or an eycgluss would best suit a " wood engraver, who 

 is frequently prcvontod from working by the lines on the 

 l:)lock becoming misty and indistinct." Bicycling is not sup- 

 posed to have any special influence on tho eyes. — F. P. Mr. 

 Allen, in using tho word "wish," neither means "an intelligent 

 desire " nor only that a special feature is presented. He means 

 t hat the colours of iJotals differ in different species according to the 

 kind of insects which it is good for each plant to attract. Ho 

 supposes his readers not wholly wanting in imagination. When a 

 writer on tho ivy speaks of it as clinging, say, to an oak, does ho 

 mean that tho plant is capable of an intelligent clasp ? — E. 0. H. 

 You are right. I had not noticed tho date. I was so startled by 

 Edward being called the twenty-fifth king that I quite overlooked 

 the wrong date. Those cigars must have left their effect on tho 

 good AbbtS oven to this very day.— G. R. Smith, L. Colmbly, E. 

 UnderH-ood, J. M. Hargreave, K. Smiles, R. F. Grierson, and others. 

 Wo cannot undertake to solve problems. They como in in too 

 great numbers. — Flsee. I regret to hear you are among surround- 

 ings so unfavourable to chess. Tho position of a chess-player 

 who can get no one to play with him at any game but draughts 

 is truly lamentable. 1 wish I know of any book on Draughts like 

 Staunton on Chess — not for my own sake (for draughts seems to 

 me a very monotonous amusement) — but that I might toll you.— 

 M. B. A. Neither can scionco understand tho attraction of gravity. 

 — W. B. W. You jump rather hastily at our expression "angiy 

 with tho drunkards," asking if anger is tho best spirit in which to 

 try to repress crime, and speaking of revenge, &c. I used the word 

 rather as implying strong objection than any fooling of personal 

 animosity. Are you quite consistent ? You are going to be a total 

 abstainer, though not one of those who are tempted to drink; yet 

 you will not join the Blue Ribbon Army. How, then, is your 

 abstinence going to do any good ? Now if wearing a blue ribbon 

 meant — let us say — that tho wearer was a reformed drunkard, 

 there might be some pluck and credit in donning tho symbol. — E. H. 

 Stevens. A cyclone is understood in meteorological phrase to mean, 

 not a storm, but a region of low jiroasurc or barometrical depression ; 

 an anti-cyclone to mean a region of high pressure. Tho terms aro 

 ill-chosen. — J. Deas. Letter marked for insertion. — O. II. T. Tho 

 inner sotelHto of Mars goes round the planet in less time than tho 

 planet takes to revolvo on its axis, because tho satollito is within tho 

 distance at which the period of revolution would be equal to that 

 of the planet's rotation. This, however, is rather how than why. 

 I cannot say why some comets revolve round tho sun in different 

 directions from the planets. If they all went tho sumo way as tho 

 planets I could not tell you why that was, either. The moon can 

 only cause tho earth to rotate moro slowly by exerting an action, 

 tho reaction corresponding to which increases tho moon's distance. — 

 W. Aenison Slater. I am interested to loam from tho Paris 

 Figaro that " Un Astronomo Anglais, M. Proctor, pcnso qn'ils" 

 (c'est k dire, les cananx supposes do Mars), " sont dua h 

 I'induslrie des habitants." It is a sliume, I think, that M. 

 Proctor never told me he thought so. — .1. F. Simpson. Many 

 thanks. Your communication unfortunately arrived when wo 

 were very much in arrears with our correspondence. Fear 

 wo can hardly find room for the notice you suggest; but if you 

 could draw up a short one, would try to insert.— I'auat.lax. These 

 angles are tho coiatitudes of Greenwich and tlio Cape, namely, 

 39' 0' and 56° 5' rcsiwctively.— Cuabon. Do not know how assis- 

 tants are appointed to Observatories and Nautical Almanac Office. — 

 II. W. P'aucus. It was tho conception thot in or near the placo 

 where tho disturbance occurs there is an explosive mixture of 



