376 METHODS IN PLANT HISTOLOGY 



of a hollow sphere filled with liquid. A fairly good and practical light 

 can be got with an ordinary lamp by allowing the light to pass through 

 a wash bottle filled with a weak solution of ammonia copper sulphate. 

 A piece of dark paper with a circular hole in it serves as a diaphragm 

 and at the same time protects the eyes from the direct light of the 

 lamp. With a good electric bulb, this not only furnishes a good hght, 

 without any glare, and with no appreciable heat, but throws a good 

 light on the pencil, which is an important consideration in drawing 

 with a camera lucida. 



Optical companies are now making excellent lights for microscopes. 

 These lights furnish good illumination and most of them have the 

 effect of good daylight; but there is still too much heat. 



If laboratory tables are small, seating only one student, there should 

 be a plug to attach the table to some convenient outlet; and also 

 another outlet on the table for the microscope lamp. If the table is 

 large, seating four or more students, there should be one or two outlets 

 on the table for each student, and a single plug by which the whole 

 table may be connected with a convenient outlet. 



For elementary classes, which are not likely to use higher powers 

 than a 4 mm. objective with an ocular magnifying five or six times, 

 individual lamps are not necessary in a well-lighted laboratory. Splen- 

 did lights are now available for elementary work, almost as good as day- 

 hght, and strong enough for ordinary dry lens microscopic work. 



