Oct. 16, 1885.] 



KNOWLEDGE 



B' T' will see the object in the direction T' B.' In the 

 case of a water-globe, an eye set at the place where B T, 

 B'T' cross, would see the object converted into a ring of 

 light all round the apparent edge of the sphere, if the 

 angle B E B' were not larger than the angular range of 

 the optical field. (A fly's multiple eye set at E would so 

 see the remote source of light.) 



Fig. 8 



Of c 



Fig. 9.* 

 the case illustrated by Fig. 9 an eye 



set where B T, B' T' intersects, would very conveniently 

 see the remote source of light. This is akin to the 

 case of the earth's atmosphere during a Inuar ruliiJSi', 

 but the varying density of the air causes tlir i-.Liinii 

 whence the sun can be wholly seen in ring fi.iin (m 1„. 

 much larger than it otherwise would be : an eye bti 

 fui'ther away would see a ring image by higher layers — 

 that is all. 



Fig. 10. 



We may, however, even in the case of shells of glass — 

 were it even flint glas-s — see a light turned into a ring in 

 the way illustrated in Fig. 10 — where C represents the 

 flame of a candle, seen through a shell of crown glass by 

 an eye at E. (A shell of crown glass must have a thickness 

 fijual to one-third the radius of the complete sphere.) For 

 water — as anyone can in a minute try with a globular 

 decanter full of water — the experiment is still more con- 

 venient. (Stand a rod upright in the bottle if you wish 

 to prevent the direct image of the flame from being seen.) 

 In this case, a .shell as in Fig. 10 would require to have 

 a thickness equal to one-fouvtli Ihr ratlin- nf the sphere. 

 But in all siich cases the light ,■<,,,., tai;j. nt liilly from A 

 and A'. [It is interesting t" m t r tliai \s liile a point of 

 light may be thus changed ini'i wliai 1^ . ];s like a very 

 tine thread of light at the vi nj i^uhhiiis ,j tlip glohe, the 

 rays by which the point is thus seiii have approached 

 (he centre by a full fourth of thr gldln/s radius.] 



The mistake miist not be made of regarding E in 

 Fig. 6, or C in Fig. 10, as foci, for they have no focal 

 character. Still less must one imagine E and C in Fig. 10 

 to be as conjugate foci to each other. 



And now a word of explanation as to my reason for 

 clearing up this whole subject till the last doubt or 

 difficulty has been (as I trust) removed, — even at the 

 risk of seeming censorious in regard to statements of 

 opinion by my friend Mr. Mattieu Williams. On 



* In order to rentier Fig. 9 [ crfectly clear, tlic reader should 

 draw straight lines A L B, A' V 1!', which were .iccidentally omitted 

 ill the drawing. 



this particular subject, or rather on that part of it 

 about which I have written here, I am well within 

 my own ground. Mr. Williams was outside his, though 

 not knowing it. There are many subjects in which, 

 were I to venture, I should be on his ground and outside 

 my own. It is very easy to fall into errors in so ventur- 

 ing, errors even which might be easily twisted so as to 

 seem to imply ignnranr.' 'n a _u~,ser sense than mere 

 want of knowledge. 1 I m i sample a mistake 



of my own — too sillv , : s Americans would 



say— ("I will [cirr. ai I -.■,■, , v seem to see, 



hut T ;. ii; , . , i If, against 



wlni I n fling, and 



the ; ■ iiceit [or 



rudii, ' -Dealing 



with hyi'otheticul cxplo.sinu.s >A mixed 'oxygen and 

 hydrogen in the sun, I said they would create an inrush, 

 because the water formed would occupy much less space 

 than the gases had occupied- forgetting that it would 

 be water in the form of steam, (that is, a vapour, not 

 a liquid), which would really be formed — and though 

 there would be, I believe, a diminution of volume, it 

 •would be nothing like what I had fondly imagined and 

 carelessly suggested. 



If readers, including Mr. Williams, will kindly under- 

 stand that I have corrected him (and on a minor point 

 my friend Mr. Ranyard) only as I wish others to correct 

 me, or as, failing that, I will try to correct myself (only I 

 always feel free to scoff a little at my own mistakes), they 

 will not I think misjudge my discussion of the Ruddy 

 Eclipsed Moon. They will see that if I have been tenax 

 propositi, I have wished at any rate to he Justus also, — 

 just as I ought to be.* Po.ssibly it may further serve 

 the purpose of showing the spirit in which I strongly 

 feel that all scientific inquiry should proceed. 



THE PHILOSOPHY OF CLOTHING. 



By W. Mattiki- Williams. 



XVIII.— COKSETS AND FK.MALP: FAhHIOSS. 

 rilHE evils of clothing having the character of bandages 

 JL were referred to at the conclusion of my last paper. 



Such banila^'es not only interfere with the free and 

 natural na-Ni an ais of the body, but in jroiorticn to 

 tluia \- they interfere witli fi..' tr.in--] im- 



tioii f . " There is still anetla . , vil, !. ni: ago 



point : I , .\ndrew Combe (" Pliysicingy aj'plied 



toil' ■' I i: ; a-ation"'). Speaking of female di-ess, 



he > I ' tiuhtness with which it is made to 



fit >■■ I lart^of the body, not only is the iu- 



b\it 1 



ed. 



rds 



one organ wit la ui all ^a IT : iiaj-, nor act rightly without 

 all sharing in the luiulii." 



I commend these wise \sii\ls to the consideration of 

 ladies who are considering whether or not they shall 

 take the really very important step of discarding corsets 

 and heavy hip-supported skirts. Their whole personal 

 welfare, their capacity to enjoy life and perform its duties, 



* But onght you to jest a: 



—Printer's dent. 



