360 



KNOWLKDGK 



September, 1912. 



h.iiul from sheets of nelaline, one red and one (jreen, wiili the 

 stars pricked out as holes in such a way that when super- 

 imposed tlie " pairs " of stars (red and green) showed up 

 briuhtly on a very dark purple background. It is needless to 

 recapitulate the many experiments undertaken, but some 

 details of the techni(|iie liually adopted and still (with some 

 modific.-itions) pursued by my firm, may be of interest: — 



(1) Mr. Heatli drew a pair of large scale star maps of each 

 selected .irea. The same stars were shown on each half, but 

 their positiins laterally varied with their ditTerences in 

 paralla.x. Ihe stars were drawn as black discs on a white 

 ground — their diameter varying with their m.ignitude. 



(2) From each half of the chart a negative was prepared 

 on exactly the same scale, and of a size suitable for a lantern 

 slide — one half (the right) was reversed, i.e., taken through the 

 back of the pl.ate, for reasons that will presently be evident. 



(3) From these negatives — (white stars on a black ground) 

 fresh positives were now prepared, in which the stars were 

 once more black on a white ground. 



(4) The next step was the sensitizing — by a modification of 

 the bichromate or carbon process — gelatine films on glass plates 

 three and a ([uarter inches by three and a (juarter inches. 

 When dry, these films were printed from the positives 

 obtained in (3), and, after exposure, developed in the usual 

 way of carbon printing with warm or hot water. If success- 

 ful, the stars, being unacted on by light, washed out completely, 

 leaving bare glass, the background being still strongly adherent 

 and insoluble. 



15) The right-hand slide was then bathed in a dye bath of 

 the correct red tint, and the left hand one in a bath of green 

 dye. The dyes were selected so as to be as near as possible 

 complementary, so that when viewed together by transmitted 

 light the films were nearly opaque (really a very deep purple 

 blue). 



(6) On now placing the two halves with the films face to 

 face, the holes in the red half appeared green, while those in 

 the green appeared red. It will now be seen why it was needful 

 to reverse one half. If not reversed the one film would have 

 had to have been placed to the outside of the slide, which 

 would not have answered. 



(7) Finally the slides were bound up into position ; any 

 little errors of printing resulting in the pictures not coinciding 

 being adjusted before binding. On viewing against a light, or on 

 a screen, each pair of stars now shows up as a red and green 

 disc, the star in each pair varying in distance from its fellow. 

 Thus, the most distant stars almost touch, while the nearer 

 ones are some w.ay apart. Spectacles with suitably coloured 

 gelatine glasses are put on when looking at the slides, when 

 the pairs combine as one star and stand out apparently in 

 mid-air. 



A curious phenomenon may here be mentioned ; if the red 

 glass is held to the right eye, and the green to the left, i.e., in 

 the same position as the colours on the slides, the stereo- 

 scopic effect is still seen, but the stars appear to stand out 

 behind the screen, and the nearest stars are seen as most 

 distant ; with the spectacles reversed, the nearest stai 

 approaches apparently nearest to the eye, in front of the 

 screen. 



Later, large transparencies, to hang in windows, were pre- 

 pared, and to my mind these are more beautiful and effective 

 and easier to see stereoscopically than the lantern slide 

 projected on a screen. For the later the disc should be 

 small, and the audience at a fair distance from the screen. 



Perhaps the most unexpected truth that these stereograms 

 have demonstrated to the public is that the largest stars are 

 not necessarily the nearest ! 



HENRY GARNfi:TT, F.C.S. 

 32, Dover Street, 



Manchester. 

 [We are pleased to announce that Messrs. Flatters and 

 Garnett are still prepared to make slides of the transparencies 

 in question. — Ens. 



SI'IXIAL AITEAL FROM THE RESEARCH DEFENCE 



SOCIETY. 



To the Editors of "Knowledge." 



Sir, — We are of opinion that experiments on animals in 

 this country should be restricted by law, that the present Act 

 should be eflficiently administered, and that the utmost care 

 should be taken to ensure the minimum of pain in these 

 experiments. 



Some of the anti-vivisection societies have lately adopted 

 methods which are grossly offensive to the public interest. 

 They have opened no less than sixty shops in London and 

 elsewhere. Most of these shops have lasted only a few 

 weeks: but they have had time to spread falsehood, prejudice, 

 hatred, and suspicion against scientific research. They have 

 also done harm to small children. It is no light offence to 

 exhibit in public not only brutal cartoons and caricatures, but 

 stuffed animals, tied down for operation, while the truth is 

 carefully concealed that no operation is allowed on any 

 animal in this country, except under an anaesthetic. 



In this connection, we would remind the public of the 

 unanimous statement of the Royal Commission : — " To repre- 

 sent that animals in this country are wantonly tortured would 

 in our opinion be absolutely false." 



The excuse is offered, for these shops, that the appliances 

 displayed in the window are actually supplied by the makers. 

 Hut if the appliances used in our Hospitals were displayed in 

 a shop-window, with models of human beings tied down for 

 operation, it would be no excuse for such a travesty, to say 

 that the appliances had actually been supplied by the makers. 



Some of these societies, having we.ilth at their disposal, are 

 able to rent shops in the most crowded thoroughfares, or to 

 -attract, by the very lavish and rather unscrupulous use of 

 money, a large audience. It seems that an effort is being 

 made to work on the mere liking for horrors, real or sham : 

 that no exhibit is too sensational, if it can serve to draw 

 attention and to excite passion. 



When we think of the vast multitudes of lives, human and 

 animal, saved from pain, disease, and death, by discoveries 

 made through experiments on animals, we cannot believe that 

 the present methods of anti- vivisection societies are acceptable 

 to sensible and honest people. 



The only way to fight these methods is to be constantly 

 publishing the facts of the case put before the Royal Com- 

 mission and embodied in its final Report. The Research 

 Defence Society, in the past twelve months, has given more 

 than a hundred addresses and lantern lectures in all parts of 

 the kingdom, and has distributed more than half-a-million 

 pamphlets and leaflets. But there is much more work waiting 

 to be done, if we had the money for it. We therefore appeal 

 for special donations, to be controlled by the Committee of 

 the Society, and to be used solely for such purposes of 

 education as public lectures and distribution of literature. All 

 cheques should be crossed Messrs. Coutts & Co., and made 

 payable to the Hon. Treasurer, Research Defence Society, 

 21, Ladbroke Square, London. W. We hope and believe 

 that this appeal, in the interest of the public, will be very 

 generously answered. 



On behalf of the Society, 



We remain, 



Yours faithfully, 



DAVID GILL. President. 

 SYDNEY HOLLAND, 



Chairman of Committee. 

 ROBERT CECIL. 

 LUKE FILDES. 

 WILLIAM RAMSAY. 

 MARY SCHARLIEB. 

 F. M. SANDWITH, 



Honorary Treasurer. 

 21, Ladbroke Sql'.\re, 



LONOON, W. 



