xxii. Proceedings. [April jrd, igij. 



90 prepared as to b'e suitable for oieproduction without the need 

 of any further work by a draughtsman. In special cases line- 

 work. \h re-drawn, but the majority pf scientific writers prefer a 

 direct reproduction of their own 'drawings. 



In the case of diagrams and other drawings in pure line, the 

 most satisfactory results are obtained by 'the Xise of a waterproof 

 Indian or Chinese ink tipon a Simooth, hard-surfaced paper, or 

 Bristol board. All the lines must be equally black and firm; if 

 Ithey are broken, or have serrated edges, the defects generally 

 become more pronounced in the reproduction. Unless it is im- 

 practicable for iiQther reasons, the original drawings should be 

 made to be reproduced to half or two- thirds their lineal dimen- 

 sions. Lines, dots, or irregular stipples may be applied to the 

 printing block by the 'engraver if indications axe given in blue 

 pencU on the correspondinjg portions of the original drawing. 



Photographs may conveniently be converted into line draw- 

 ings by drawing over the outlines with waterproof ink and then 

 bleaching out the original print. 



For rapid effects the use of " scraper-boards " is sometimes 

 convenient. These boards have a chalk coating and are obtain- 

 able in a variety of forms ; they are covered With printed and 

 lembossed lipes. The shadows of the drawing are made with a 

 carboin pencil, the high lights being scraped away with a knife. 



Photographs for reproductiofi by .collotype or by the half- 

 tone process are preferably black, glossy " bromide " prints, or 

 ■' gelatimo-chloride " prints of a purple-brown tone. If a number 

 of separate prijnts are to be reproduced together as a page, they 

 should, as far as possible, be similar in strength and colour. 



Sepia wash drawi;ngs are more satisfactory for photographic 

 reproduction than those made in pure black and gray. The 

 quality of the reproductioin of a suitable drawing by the collo- 

 tyfpe process, or by the half-tqne process under satisfactory con- 

 ditions is indubitable); a,nd it is questionable whether the expense 

 O^ preparing a chalk lithograph can be justified. 



The correct translation of coloured objects or drawings into 

 monochrome reproductions by photography is not possible by 

 means of the ordinary silver bromide dry plate, for the sensi- 

 tiveness of the latter includes only the violet and blue re^ons 

 of the visible spectrum. The applications of photography to 

 scientific purposes and to reproduction work have been greatly 

 increased by thje commercial production of panchromatic dry 

 plates, which are sensitive to^ the entire visible spectrum. By the 

 Use 'of tbes'e plates, in conjunction with suitable colour light 

 fitters, wthich tra^nsmit only light of the required spectral regions, 

 it is possible to obtaiji photographs of coloured objects which 

 reproduce thdix true colour values or secure, maximum contrast. 



