March, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



383 



occupied with asther; that the molecules arc in louch with 

 one another and occupy all the space that gravitation (pres- 

 sure) permits; that the only other force acting- on the mole- 

 cules is that form of gravitation named cohesion ; that the 

 cohesion that acts on a molecule by contact with its neigh- 

 bours is greater, because of the interior space, than the 

 cohesion tending to solidify the molecule ; that the molecule 

 consists of superposed globular shells of the elements that 

 compose it ; that that expands the molecule by entering it 

 as vibrating ather which expends its vibrations in the work 

 of expansion and thereafter remains as what is called latent 

 heat ; that when the contained eCther leaves the molecule by 

 the need to level, or, as it may be called, equalise itself, it is 

 thrown into vibration and appears as radiant heat. 



The heating of the iron makes its crystalline molecules 

 expand and approach the globular shape. There are then 

 small S[)ac"s among the molecules that there need not be in 

 the cold mass if the crystalline shapes are perfectly arranged 

 together. The jether in these sinall interspaces in the hot 

 mass is in violent vibration, and this motion, in addition to 

 the production of radiant heat and lig'ht, is some of it ex- 

 pended in displacing the crystalline molecules, with the re- 

 sult that the mass is increased in dimension. 



No theory that includes Hying atoms can explain this 

 e-xpansion of the iron. 



W. F. BadcjI.ev. 



February 4, igo6. 



Answers to Correspondents. 



account with 

 isks llic cause 



sketch 

 of the 



twig s 

 bed in 

 Scott 

 ustra- 

 of the 

 in the 



Mock Suns. ~ W. II. ('. sends 

 from Canada of ".Sun Dogs," a 

 phenomenon. 



These " mock mmis " h;i\c lor long been \\( II k 

 Mo.st books on nirh'orology refer lo them (r.,/., Ilar 

 Ai'iial IVdilil). .Similar phenomena have been dcscri 

 niany accounts of .\rclic or An'arclic regions (Capt 

 m the royaijc „f the " Discovery " gives a coloured il 

 tion ol one). The effect is caused by the polarisation 

 light en striking the small crystals of ice suspended 

 ;iir. 



The Star towards which the Earth Is Travelling 



.\. b. .\l. .isl-s whclh.r Ihis si.ir is visible 10 Ihe naked eye, 

 and wh.-it si/e it is as comp.ared to .Sirius. The whole solar 

 .S}stem IS moving in (he direclion of Vega, a star of the 

 1st magnitude. This is proved bv the fact that the stars in 

 this neighbourhooil are gradu.-illv opening outwards, while 

 those in opposite direction are closing together. Vega .ap- 

 pears smallr'r than Sirius, the relative I'nagniludes' being 

 0.1 ;iiul t..^ respectively. ' '^ 



Occultation of Star by the Moon. — T. .\. I.,,wnd(s wiius 

 describing accuratelv the "strange sight" he saw on 

 1-ebruary ^ at >o minutes past 5. A sm.-iU star w;is close 1,, 

 the moon an<l .appeared to be in front of the dark part of it 

 It disa!)i)ca_red at 27 minutes past 5. Under the " Face of 

 Mie Sky in our l-ebruarv number one niav see that on 

 bebruaiy 3 at 5.2;, the lirsl magnitude star .Xldebar.an w;is 

 in occultation with the moon. The bright star close to (he 

 edge of the dark portion of the moon "would be verv li.able 

 to have the .appeanince of being in front of it. Se\er.il 

 smaller occulUlions occur this month ((•((/(■ " l'"aic of ihe 

 Sky "). 



Frogs found in Rocks. IC. BraddocU asks for information 

 respectiiif; llie alle,i;ed finding of live frogs in rocks. Mr. 

 l-rank Huckland went into this subject many years ago, and 

 the conclusion that he came to was that iu every well authen- 

 ticated case It was found that some crack or other means 

 existed by which the fro;; eoiild obtain air and probahlv insect 

 food. 1 hough such reptiles undoubtedly live to a great a"e 

 It seems probable that in these cases the frog or tadpole may 

 have become caught in some crevice, and hit by bit have worn 

 a larger hole for itself as it grew. 



PhotogrscpKy. 



Pure and Applied. 



By Chap.man Jones, F.I.C, F.C.S., &c. 



T/tc Colour ScmalioHS. — Thcrt; are variou.s opinions 

 as to the principles upon which colour photography 

 should he ba.sed. .Some consider that four colours are 

 necessary, others that three colours are sullicient, and 

 that there is considerable scope for choice in the selec- 

 tion of the three, but there can Ijc no doubt that the 

 present position of colour photography, if not its very 

 existence, is largely due to endeavours to record 

 separately the colours that correspond to the three 

 sensations, so that these may be stimulated by the 

 various parts of the finished photograph in the same 

 proportions as by the corresponding parts of the 

 original. From this point of view the colour sensa- 

 tions are of prime importance to the photographer. 



.Since 1899 Sir William .\bney has been engaged in 

 revising the details that he then published, expressing 

 the three .sensations in terms of luminosity, and he has 

 lately published the results of his work.' He has ob- 

 laincd results that were impo.ssible before, by a modi- 

 liiation of his well-known colour-patch apparatus. 

 Light from an arc lamp is passed through a train of 

 two prisms, and then by means of a .semi-silvered 

 mirror a part is di\erted, and so two spectra are 

 lormed, each of which is recei\ed on a plate with three 

 adjust.ible slits in it and a lens beyond for combining 

 the transmitted lights to form a piitch. Thus on the 

 screen two adjacent adjustable colour patches are 

 formed, and also a patch of white light obtained by a 

 mirror by reflection from the first' face of the first 

 prism. The luminosities of the patches of light are 

 regulated lor photometric purposes by re\-ol\ ing .sectors 

 as usual. 



.\ re-delermination of the sensation cur\cs bv means 

 nl this more efficient apparatus, in conjunction with 

 oilier experiments, leads to the conclusion that there is 

 no fourth .sensation excited by \iolet light, as has l)een 

 suggested by Burch. The revi.sed ciirves show onlv 

 slight alterations from those previously given, and this 

 chiefly in the green, where the thre\; sensations o\erIap 

 and gi\e an admixture of white with the predominant 

 colour. The curve of this " inherent white " shows 

 no sudden rise in any colour as was represented in the 

 curves previously given. The amount of blue sensa- 

 lion ill the yellow and green of the spectrum has also 

 been corrected. Full tables and curves, and a descrip- 

 tion of their applications in three-colour photography, 

 are given- in the Philoso|)hical Tran.sactions of the 

 Royal Society (series .\, vol. J05, pp. 333-^55). The 

 paper can be obtained separately from Klessrs! Dulau, 

 of Soho .Square, for one shilling. 



The Bh-iidiiiig-Oul Threc-CoUmr Profm.— The 

 principle involved in this method of reproducing colour 

 1)\ exposure to light of the prepared material under the 

 original is of a very simple character. 'i'he three 

 lU'cessarx colours are conlained in Ihe sensitive film, 

 and on exposure the colouring matter that ab.sorbs light 

 is bleached while that that transmits Ihe light remains, 

 or, at least, remains longer than the others. Red light, 

 lor example, or Ihe light that passes through the^•ed 

 p.irts of the original, being transmitted bv the red dye 

 h.is very little effect upon it, but it is ab.sorIx*d bv the 

 lilue ;ind yellow dyes bleaching them, and leaving a red 



