ELEMENTARY PHOTO-MICROGRAPHY. 27 



which a tube bearing the bull's eye may slide to 

 and from the lamp) supported by two loose ends 

 free to rise and fall. The bull's eye can be raised 

 or lowered at will, and the centre of the flame can 

 thus be adjusted to suit the centre of the microscope. 

 All adjustments are easily made, and, having once 

 been perfected, the time required for setting it in 

 position for work is reduced to a minimum. 



A metal chimney is preferable to glass, and a 

 shade to drop over the lamp chimney is desirable. 

 To set the lamp properly the flame is first turned 

 gradually up to its working height, and put with the 

 edge of the flame (not the flat) towards the con- 

 denser. The flat side of the bull's eye is put next 

 the flame, at its proper focal distance. Having 

 done this, the photographer's next step is to look 

 right into the lens through a, pair of neutral tint 

 spectacles, and to raise or lower the flame until the 

 whole is brilliantly illuminated. If dark spots ap- 

 pear in the lens it is moved towards or from the 

 flame to get a bright circle of light. If this does 

 net give the desired result, raising or lowering the 

 lens must be tried. A little experimenting will soon 

 give the correct position. 



One advantage of an oil lamp is the absence of 

 that intense heat which gives the user of limelight 

 so much trouble. 



MAGNESIUM. 



Magnesium ribbon burns at the rate of about 

 twelve inches per minute. It is purchased in coils, 



