THE BOOK OF THE LANTERN. 99 



briefly this. He works with a hard pencil on a piece of 

 very finely-ground glass ; afterwards filling in the outlines 

 thus made with water colours, and applying a coat of var- 

 nish so as to give the necessary transparency to the picture. 

 This method he brought before the Royal Microscopical 

 Society, and the following extract from his paper describes 

 the matter so clearly that all will be able to follow his 

 directions : 



" Most working microscopists have felt the necessity, in 

 reading papers on their work, of accurate illustration. 

 These enlarged drawings fail in matter of detail, unless 

 extravagant labour is expended, and considerable skill 

 employed. Even then the light of an ordinary lecture 

 hall is not enough to enable the most distant of the 

 audience to see them. It is only by means of the limelight 

 and transparencies that really useful illustrations can be 

 given. But here the difficulty is to prepare them accu- 

 rately and inexpensively. Photography cannot be employed 

 in all cases ; and even where it can be, it involves more 

 labour than most microscopists can afford. Drawing and 

 painting on glass in the usual method is an art that it takes 

 years to learn ; and to employ one who has learned it to 

 draw from nature a highly-magnified object, would be to 

 introduce unnumbered errors of interpretation, unless our 

 artist be a microscopist himself. 



" I obviate all these difficulties by the following method : 

 On finely-ground glass, drawing with a black lead pencil 

 is as easy as drawing on London board. I get four inch 

 squares of glass to suit my lantern, carefully ground on 

 one side like the focussing glass of a camera. Now with 



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