2 THE USE OF THE MICROSCOPE 



100 to 1,000 magnification remaining more or less isolated 

 from daily life. The twin-objective (Greenough) binocular 

 will supply such low-power pictures, giving an image to 

 both eyes in relief. Training in the use of the microscope 

 should be, it seems, a series of steps from the known to the 

 unknown: from the magnification of 1.0 of the eye focused 

 (accommodated) for reading at 10 inches, to the maximum 

 useful magnification of the best oil-immersion objectives; 

 which may, with all adjustments correct, reach nearly 

 1,400. 



Stages in Microscopical Training. — In the use of the 

 medium or high-power compound microscope in scientific 

 work (apart from such an obvious requirement as the auto- 

 matic movement of the slide in the opposite direction to the 

 required movement of the image), there are certain proce- 

 dures which must be learned in order to obtain a perfect 

 microscopical image. They include the following points : 



The constant employment of the fine motion of the 

 microscope is necessary wdth medium or high powers. 

 This uses the upward and downward movement of the 

 focus plane as a substitute for the accommodation of the 

 eye for different depths. The constant employment 

 of the fine motion has been sometimes said to mark the 

 experienced microscopist. But it is, in fact, only the 

 A of microscopy, with the rest of the alphabet to follow. 



A second important step in practical microscopy is 

 the solving of the cover-glass problem. It includes the 

 learning of the star test. (This will be discussed in 

 a subsequent chapter.) The simplest solution is probably 

 the best. 



The constant adjustment of the iris diaphragm of the 

 focused condenser (immersed if necessary) to get the right 

 aperture in the condenser for each objective and object, is 

 required in order to procure the clearest images and those 

 showing most detail. The aim should be a condenser cone 

 nine-tenths of the aperture of the objective, without glare. 

 The knob which moves the condenser iris should be worn 

 shiny by incessant use. 



