8 



HOW TO PHOTOGRAPH 



for washing negatives ; a porcelain dish for 

 toning prints, and another for fixing them. 

 Racks may be used for drying the negatives, 

 but in winter, standing them up on a warm 

 mantle-piece is as good a plan as any, un- 

 less the plates be made with very soft gela- 

 tine, when catastrophes may be expected 



in the shape of distortion of the image, or 

 even melting of the gelatine. 



Lesson III. — Illuminating Apparatus. 



In this country photo-micrography by 

 daylight is troublesome and unsatisfactory. 

 The sun shines brightly during so few 



NAVICULA LYRA, X 900. 

 Taken with a Siebert's immersion: Exposure about fifteen seconds 

 to magnesium ribbon in a holder. 



months of the year, and is s > fickle when 

 he makes his appearance, that the photo- 

 micrographer is compelled to fall back on 

 artificial light to do his work. In many 

 respects sunlight would be preferable, were 

 It only always at the command of the pho- 

 to- micrographer ; it costs nothing, is rapid in 

 its action, is more powerful than any other 



light, and exhibits objects illumined by it as 

 we are accustomed to see them. The chief 

 disadvantage of using the sun as a source of 

 light is, that, owing to the earth's motion, the 

 direction of the light is continually altering, 

 necessitating the use of an expensive reflect- 

 ing instrument, called a heliostat, to keep the 

 rays constantly in any required direction. 



