SCREENS AND LANTERN ACCESSORIES 127 



enhanced. Such a screen, faced with mineral matter, per- 

 ceptibly improves the light for microscopic and physical 

 demonstrations. 



Small occasional screens are often needed in experimental 

 work, and sometimes in a drawing-room. The cheapest and 

 handiest material for such, is apiece of Whatman's continuous 

 drawing cartridge paper. This can be obtained 60 inches 

 wide of any length for a few pence per yard, and may be at- 

 tached to a small roller. 



68. Transparent Screens. For common lantern work, the 

 thinnest material in one piece ten feet square may be used, 

 strained tightly, and wetted before the exhibition. The simple 

 fact that the picture ' shows through ' in this way, sufficiently 

 accounts for the superiority of plaster or opaque surfaces over 

 a sheet. A thinner muslin material is also employed, and 

 this will have to be joined with as fine and imperceptible 

 seams as possible. A transparent screen more than ten feet 

 square is never used. 



Transparent screens were very usual in early lantern days, 

 when nine-feet discs were all that could be ventured upon. 

 They are generally now confined to folding-doors in private 

 houses, or semi -microscopic exhibitions. 



The best transparent screen for microscopic work is one 

 made of tracing paper. This can be had in continuous rolls 

 5 feet wide, and a screen of this width, with a light portable 

 frame, is both very handy, and gives some charming results, 

 though not equal to an opaque screen in illumination. Such 

 a size is even large enough for pleasing drawing-room exhibi- 

 tions with oil lanterns, which can be made on this scale with? 

 out leaving the room in darkness. 



69. Sizes of Screens. The limits of transparencies have 

 been stated. Faced screens are always mounted on a rod and 

 roller, just like a map, and hence more than 12 or 14 feet wide 

 is awkward to carry. For a hall there is no limit to these 

 screens beyond the size of the wall on which they have to be 



