36 



lamplight, but, if necessary, the condition of the light may be improved by means 

 of a collective lens placed before the microscope (see under heading of Accessory 

 Apparatus, p. 111). When, however, the available working distance is small, an 

 appliance for passing the light through the objective becomes necessary. This 

 requirement is met by the *Vertical Illuminator, No. 42 (Fig. 15), supplied by 

 us now for a considerable time past. The rays issuing from the source of light enter 

 through a lateral opening in the mount of the apparatus, strike the hypotenuse 

 surface of a reflecting prism, which covers one half of the aperture of the 

 objective, and are thence totally reflected through the objective and concentrated 

 upon the object. 



Price of Vertical Illuminator: Marks 18. . Code-word: Paramento. 



B 



Fig. 15. 

 Vertical Illuminator, No. 42. 



A: view of same (partly sectional) 



attached to the lower tube and the 



objective C the latter in short 



A mount; p: reflecting prism; B: plan 



view; K: milled knob for revolving 



the prism. 



(Full Size.) 



As it is of importance for the efficient working of the apparatus that the upper lens 

 of the objective should be as close to the prism as possible, most objectives intended for 

 work with a vertical illuminator should be fitted in special mounts. 



Preparations under a cover-glass are not suitable for examination with the apparatus; 

 the higher powers (apochromatic objectives from 8 mm equivalent focus and achromatic 

 lenses from D upwards) require to be specially corrected for examining uncovered objects. 

 In working with oil immersion, on the other hand, the use of cover-glasses is again admissible. 



It is furthermore of great advantage to reduce the diameter of the image of the 

 source of light so that the illuminated portion of the object may not be greater than 

 the area of the visible field of the objective used. The readiest means to attain this 

 object is by placing a collective lens with iris-diaphragm in the most favourable position 

 before the microscope. 



For fuller particulars see the Directions for using the Vertical Illuminator, a copy of 

 which accompanies each instrument supplied by us. 



