212 THE BOOK OF THE LANTERN. 



has to be spread over a screen of even moderate propor- 

 tions, the illumination of the whole is so insufficient that 

 although near observers are able to note that the disc is 

 covered with a network of exquisite detail, those who are 

 placed a few yards away cannot distinguish anything of the 

 kind. If this is the case with those whose sight is perfect, 

 how much more true it must be of the large number of 

 persons who are less favourably endowed. Probably the 

 difficulty may be remedied at an early date by the use of 

 the electric light, which is far more brilliant than the best 

 limelight possible, and I know that experiments are 

 being carried on in this direction ! In the meantime, we 

 must look for other means of projecting the image of 

 microscopic objects on a screen if we require such illus- 

 trations for a large number of spectators. I recommend 

 the employment of photo-micrographs of the size of the 

 ordinary lantern-slide, viz., 3J x 3J in. as the best way out 

 of the difficulty. I am, of course, aware that a photo- 

 graph of an object is not in many cases so good as the 

 object itself. While this is true, it is also true that there 

 are a great many preparations which cannot be satisfactorily 

 shown by any kind of projecting apparatus, but they can 

 be made to yield photographs which can be exhibited by 

 the optical lantern. There are many different ways 

 of producing photo-micrographs. Some workers use the 

 most complicated apparatus, whilst others seem to obtain as 

 good results with rough home-made appliances. But so it 

 is in every branch of science. Somebody wittily divided 

 microscopic workers into two different species. He dubbed 

 the first of these " Brass and Glass," and the second 

 " Bug and Slug." The first are the possessors of the 



