284 



♦ KNOWLEDGE ♦ 



[April 3, 1885. 



SBIPLE METHODS OF MAKING 

 LAXTERN-SLIDES. 



By W. Jerome Harrison, F.G.S. 



THE optical laiitern now holds a very high place as an 

 article of scientific apparatus. In one or other of its 

 forms it is to be found in almost every laboratory, while the 

 itinerant lecturer would bo badly ofl', indeed, without its 

 aid. Moreover, in many homes the lantern is regularly 

 used as a source of pleasure and instruction for the family 

 circle. The extended use of the lantern has produced a 

 corresponding improvement in the production of the slides 

 by which its beautiful pictures are produced. The leading 

 professional firms — York, Valentine, and others — now issue 

 slides of the highest quality at exceedingly moderate prices. 

 But it is the experience of every one who possesses a lantern 

 that it is very frequently desirable to copy diagrams from 

 books, or to exhibit tables containing figures, «fcc. Of 

 course, such diagrams, ic, are frequently done on a large 

 scale upon canvas or paper, with the aid of stencil-plates, 

 but this is a far more laborious task than the preparation 

 of a lantern-slide. 



It is especially desirable, too, to exhibit pictures of what 

 one has actually seen, during excursions in the field, or 

 through the telescope or the microscope, and it is seldom, 

 indeed, that slides of the exact places or objects can be 

 purchsised. Since the introduction of the " dry-plate " 

 process into photography, the number of those who practise 

 what now need not be the " black art " has immensely in- 

 creased. Thousands of amateurs succeed in taking very 

 good pictures indeed, and many of onr scientific societies 

 have distinct sections for the study of photography, con- 

 sisting of members who devote themselves to special objects, 

 such as the representation of famous trees, or the geological 

 features of qunrrien, railway cuttings, ic. ; or, it may be, to 

 stellar photography. The " negatives ' which are thus 

 obtained will, it is true, yield a large number of "positive" 

 prints, but, for the purpose of exhibition to an audience, 

 transparencies made from the negatives and shown on the 

 screen by means of a good lantern form by far the best 

 mode of illustration. 



The following notes include brief descriptions of simple 

 methods of which I have availed mj.^elf at various times 

 for the production of lantern-slides. For many of them I 

 am indebted to the fertile mind of Mr. Woodbury, the 

 introducer of the Sciopticon Lantern. I shall first speak of 

 methods which do not require the aid of photography, and 

 then pass on to the description of a photographic process 

 which is rapidly coming into favour — the use of dry plates 

 coated with gelatine, in which chloride of silver has been 

 emulsified. 



1. Tin FOIL. — Take a piece of stout cardboard 3} in. 

 square (the regulation " lantern-slide " sizr) and cut out a 

 hole in the centre, larger or smaller according to the size of 

 the diagram you wish to copy. Paste a piece of tin-foil 

 over the hole. Now punch out in the tin-foil holes to re- 

 present the subject of the diagram. The corkboiers used 

 by chemists are very useful for this purpose. If it is 

 desired to represent the planets, small pieces of coloured 

 gelatine (such as is contained in bon-bons) may be gummed 

 over the hole in the tin- foil, and the characteristic features 

 of the jilanet — as the belts of Jupiter — may be lightly 

 sketched on the gelatine with Indian ink. For the illus- 

 tration of double stars this method answers well. Nebul.-e, 

 too, can be shown by delicately pricking the tin-foil with 

 the point of a needle. The needle-points for this class of 

 work are male by forc'ng the eye end of a needle into 



the end of a wooden penholder : this is best eflfected with 

 the aid of a pair of pincers or pliers. 



2. Opaque Varnish on Glass. — For the representation 

 of the radiant-points of meteor streams I have poured a 

 pool of Bates' photographic black varnish upon a clear 

 piece of glass. When the varnish is dry, or nearly dry, 

 lines may be drawn through it with the point of a knife, 

 or with a needle-point. These lines will be shown as white 

 upon a black ground when thrown upon the screen by the 

 lantern. 



Smoked Glass. By moving a piece of clear glass for a 

 minute or two over a candle-flame it will become coatetl 

 with a dense deposit of carbon. Lines may be drawn 

 through the black deposit with a fine steel point, and these 

 lines, as in the last method, will be visible upon the screen 

 as white streaks. The smoke from a small lump of burn- 

 ing camphor blackens the glass very quickly and thoroughly, 

 and I prefer it t > the candle. To prevent the black from 

 getting rubbed off, strips of cardboard a quarter of an inch 

 wide should be gummed round the margin of the slide (the 

 black should be previously removed from the margin). 

 Then a second piece of clear glass should be gummed or 

 glued to the cardboard so as to cover over and protect the 

 blackened surface. Very good eflfects can be produced 

 upon glass surfaces treated in this way. I have effective 

 diagrams of the electric spark taken between terminals at 

 distances varying from one inch to two feet, physiological 

 sections, ifec. The varieties of clouds can be shown exceed- 

 ingly well by using a dahber made by tying a bit of 

 chamois leather over a wooden point, as the sharpened 

 end of a penholder. By pressing the thumb upon the 

 blackened glass, fine impressions of the furrows in the skin 

 can be obtained, and it is very amusing to compare the 

 thumbs of various individuals in this way — no two are 

 exactly alike. 



The methods ."o far deicribed give white lines upon a 

 Vjlack surface. The remaining non-pbotographic processes 

 give black lines upon a white surface. 



4. Clear Glass Coated with Gum Dammar — It is not 

 possible to work effectively upon clear glass with ink or 

 pencil. The hard, smnoth surface has no "tooth," as 

 photographers say, and will not "take " the pigment. But 

 it is p ssible to coat the glass with some transparent, 

 co'ourless medium of a softer nature, on which lines may 

 readily be drawn. For this purpose I use a solution of 

 gum dammar in pure benzole — sixty grains to the ounc& 

 The gum dissolves readily without the aid of heat, and the 

 solution should be passed through filter-paper. The glass 

 to be coated should be cleaned and slightly warmed. The 

 varnish may then be poured on in a pool at one comer, and 

 caused to run all over the plate, the excess being allowed 

 to run off" from another corner into the bottle again. 

 Additional toughness may be given to the gum dammar by 

 the addition of a few drops of a clear solution of india- 

 rubber in benzole. 



5. Ground Glass coated with Canada Balsam. — The 

 surface of very finely-ground glass admits of drawings of 

 great delicacy being made upon it by the aid of a sharp- 

 pointed hard lead-pencil. When the drawing is completed, 

 the glass should be warmed, and then coated with a mix- 

 ture of Gana la balsam and turpentine, about two or three 

 ounces of the former to one ounce of the latter. The slide 

 should then again be warmed, when the turpentine will be 

 driien off by the heat, while the balsam will remain as a 

 clear, hard, transparent coating, which fills up all the 

 little hollows in the ground-glass, and makes it perfectly 

 transparent. The Rev, W. H. Dallingerhas employed this 

 method with great success in the representation of micro- 

 scopic organisms. 



