90 BINOCULAR MICROSCOPES [Ch. Ill 



of white cloth, a light-colored insect, a feather, or any other object 

 which it is desired to see. Place the microscope where there is a good 

 light and look at the object. When seeing with both eyes the stereo- 

 scopic effect will be very striking, and one can see the different levels, 

 etc., as with the naked eye. 



For dissecting and for dark objects the lighting must be brilliant. 

 Sunshine on the specimen is often none too strong, but as that is not 

 stationary and not to be had at all times, it is usually more satisfactory 

 to use a small arc lamp (fig. 49) or a projector with a concentrated or 

 stereopticon type mazda lamp. If the light is concentrated upon 

 the mirror for translucent specimens or directly upon the opaque 

 specimens there will be sufficient light to give satisfactory images. 



§ 149a. Correct movement of the specimen or instruments under an 

 erecting microscope. — For one who has become thoroughly trained in using 

 the ordinary inverting compound microscope it is very difficult to make the 

 proper motions to move the specimen, or to move the dissecting instruments 

 correctly under an erecting compound microscope. This illustrates the power 

 of training. The beginner with the inverting microscope finds it hard to move 

 his hands in the opposite way from what his eyes dictate, but when the correla- 

 tion between the appearance and the motion necessary has become fixed, it is 

 equally difficult to move the hands in the direction which the eyes indicate, 

 although it is known that this is now correct. This difficulty is soon over- 

 come by practice. 



Under the simple microscope, however, in which there is no reversal or in- 

 version, the eyes and hand work together automatically as with the naked eye. 



Single-Objective Binocular Microscopes for All Powers 



§ 150. Single-objective binoculars. — This is to be used for 

 looking at microscopic specimens exactly as a monocular compound 

 microscope. That is, the lighting, numerical aperture of the condenser, 

 and all the work done with it is the same. The only difference is that 

 the two tubes are to be arranged at the right distance apart to give 

 binocular vision as discussed in § 147. 



If the two eyes differ, then one of the tubes must be focused to make 

 the necessary compensation. 



With the excellent binoculars now available, there is nothing done 

 with the monocular microscope that cannot be done with the binocular, 

 and for many workers the use of the two eyes, as has been so long 

 contended by the English microscopists, gives much relief for long- 



