398 



SUMMARY OF CURRENT RESEARCHES RELATING 10 



a suitable magnification of the light source. The ground glass disk 

 was made out of the thinnest possible object-glass, and its corners wore 

 melted off so that it did not fit quite perfectly over the diaphragm, the 

 purpose being to avoid displacement of the object by air currents which 

 might otherwise intrude between the ground glass and the object slide : 

 this plan gives a ready passage to such air-currents. A copper ring 

 suitably inserted prevents impact of the ground glass disk on to the 

 object slide. The above description applies to a stand fitted merely 

 Avith a diaphragm and without an Abbe condenser ; but in the case of a 

 stand fitted with a condenser, the above disk must be applied under the 

 condenser lens. 



Watson and Sons' 

 fits over the eye-piece, 

 against a divided circle. 



Eye-piece Analyser.* — This analyser (fig. 63) 

 has a large field-prism, and rotates with index 



Fig. 63. 



Fig. 64. 



Koristka's Illuminator for Opaque Objects.! — This piece of appa- 

 ratus (fig. 64) is principally intended for the study of metals. It fits 

 into the tube of the Microscope, and contains a totally reflecting prism 

 for receiving lateral light, and reflecting it through the centre of the 

 objective on to the preparation. An iris-diaphragm in front of the prism 

 serves to regulate the incident light. The whole of the prism arrange- 

 ment with the iris slides in a groove in such a manner that any desired 

 portion of the field can be illuminated, and the best position of the 

 prism ascertained. The light should be directed on the iris by an 

 illuminating lens. 



Hall's Grip Nose-piece.J — This fitting (fig. (55), made by W. Watson 

 and Sons, is placed at the lower end of the Microscope tube, and the 

 objective is slipped into it after pressing the handle. On releasing the 



* W. Watson and Sons, Ltd., Catalogue, 1909. 



t F. Koristka, Milan, Catalogue xiii. (1908) Microscopi ed Accessori, p. 57. 



X W. Watson and Sons, Ltd., Catalogue, 1909, p. 110. 



