222 THE AMEKICAN MONTHLY [October, 



first. The object having been magnified by this lens, its image is re- 

 ceived by the eye-piece, so named from being placed at the upper end 

 of the microscope tube next the eye of the observer, and where it under- 

 goes a further amplification. The microscope tube is mounted on a 

 stand, and the focal adjustments are made either by moving the tube up 

 and down through a cloth-lined tube, through which the microscope is 

 made to slide, or b}^ a rack-and-pinion movement, which is the more 

 convenient method. 



Below the stage on which objects are placed for examination, is sus- 

 pended a mirror, having plane and concave silvered surfaces, by which 

 daylight, or that from a lamp, is transmitted through the object. Be- 

 tween this and the stage, a revolving disc of metal, termed the dia- 

 phragm, and having apertures of different sizes, is fixed. This enables 

 the observer to regulate the amount of light received by the transparent 

 object in such a degree as to reveal details in it, which otherwise might 

 be lost in a flood of unnecessary light. The student having a micro- 

 scope of this plain and simple description, needs but a condensing lens, 

 either attached to the stage or separately mounted on a foot for proper 

 lighting of opaque objects, to have enough to enable him to begin his 

 attack on the world of wonders lying at his feet. Before he does so, 

 however, a few directions as to his meithod of working may be in place. 



Lighting the Object. — The light employed for microscopical exam- 

 ination may be either the light from a good lamp or daylight. Of these, 

 the latter is preferred, as less fatiguing to the eyes, besides giving a 

 more correct view of the object examined. The light from a white cloud 

 in the northern sky is especially recommended, but where this condi- 

 tion is unattainable, a piece of white paper placed on the mirror fur- 

 nishes a very good substitute. As the student may not have the oppor- 

 tunity during daylight for the investigation, he must perforce use lamp 

 light, and by placing a lump of camphor about the size of a walnut into 

 the reservoir of the lamp, and burning some well purified paraffin, a 

 brilliant white light can be obtained, wdiich may, at any time, be soft- 

 ened by reffection from paper. 



The lamp should be placed at the observer's left hand, and in advance 

 of the microscope ; it is not then in the way of his right hand and any 

 apparatus placed there for use. 



Simple Apparatus. — The student in microscopical investigation 

 should begin his investigations by the study of the simplest subjects. 

 Unfortunately the tendency of most newly-interested observers is to rush 

 into an examination of the higher and more complex objects before they 

 are thoroughly versed in the appearance presented by those elements of 

 which the higher classes are constructed. It is well if the student can 

 restrain his ardor till he has acquired familiarity with such simple 

 objects as the hairs of various animals, fibres of cotton and wool, the 

 starches of wheat, potato, and rice, and such subjects which may be 

 found ready at hand. These may be followed by the examination of 

 the several elementary tissues entering into the formation of the animal 

 and vegetable structures. 



When he has familiarized himself with these comparatively simple 

 objects, he may then pass on with profit to the examination of the 

 higher structures, when his preliminary training will be turned to ad- 

 vantage in the ready recognition of many of his early acquaintances 



