22 THE CANADIAN NATURALIST. [March 



and a compound object glass — divisible into 1 in., ^ in. and Jin. 

 powers — giving a range from 40 to 400 diameters. An opaque 

 condenser on separate stand, stage forceps and live box are also 

 packed in a neat mahogany box with lock and key. A polari- 

 scope is added for £2 extra and the whole is a thoroughly good 

 working instrument. I have used one for years as an extra 

 laboratory instrument, and have been well satisfied with a large 

 number which I have examined and recommended to students. 



Similar instruments for about the same price may be obtained 

 from J. B. Dancer, Manchester, or Abraham & Co., Liverpool; 

 but in the choice of such an instrument T call the attention of 

 the student to certain requirements : — 



1st. Steadiness of the instrument combined with inclined 

 Dosition. 



2ndly. Correction and definition of object glasses. 



3rdly. Enlarged field of view. 



4thly. Free stage movement. 



5thly. Good illumination above and below the stage. 



6thly. Smooth rack work adjustments. 



A few words on each of these points may be useful to the 

 inexperienced. 



The steadiness of your instrument and of the table or floor 

 upon which you are working is essential to accurate observation, 

 round stands are generally unsteady, and the tripod should there- 

 fore have the preference. Inclination of the Microscope has a 

 tendency to increase any vibration, but it is a valuable motion 

 which the student's Microscope should always possess. The 

 upright position is not only fatiguing, but a source of error 

 from the specs which float upon the watery huuiour of the eye 

 and collect over the pupil, disturbing correct vision. All perpen- 

 dicular stands should therefore be rejected by the student, and 

 for prolonged work the Microscope should be inclined at the 

 most convenient angle for the height of the sitter. 



The definition of the object glasses is the test of their value. 

 Probably the student must take them on the faith of the manu- 

 facturer; but if he has the judgment to select, he will give the 

 preference to the glass which in its highest power will give him a 

 good stereoscopic view of a raised object such as the pollen of 

 mallow or hoUyock, and which will define the markings upon starch 

 granules, such as arrowroot and tons les mois, without coloured 

 fringes or distortion of the forms; at the same time it is desirable 



