414 Notes. 



The Ashc-Finlayson " Cow para scope." 



(An instrument to facilitate comparisons being made between different objects 

 by projecting their images together into the field of the Microscope.) 



By D. Finlayson, F.L.S. 



The desirability of some method whereby two objects may be 

 simultaneously examined in the same field of view, is often ex- 

 perienced by microscopists and analysts, especially by those who 

 are engaged in work which necessitates frequent comparisons being 

 made between objects which present very similar appearances. 



It seems strange, therefore, that no attention, so far as can be 

 ascertained, has hitherto been directed towards the construction 

 and perfecting of apparatus to serve this purpose. 



In examining objects of a totally different appearance and 

 structure, the use of such an adjunct would be obviously un- 

 necessary — in fact, its employment would be a positive disad- 

 vantage, by its limiting the area of the object seen to one-half of 

 the field of view ; but when the differences of structure or variations 

 of form are too slight to be readily perceived, then the ability to 

 place by instrumental means the subject to be examined, and the 

 standard by which it is to be compared, side by side, in the same 

 field, is an advantage so great that its value need not be dwelt 

 upon. 



The purpose in view could be carried out most effectively by 

 the construction of a complete Microscope specially built for the 

 purpose, but as such an instrument would necessarily be expensive, 

 and limited in the scope of its general utility, it seems desirable 

 to confine the problem to the construction of an apparatus which 

 can be used as an adjunct to, and in conjunction with any existing 

 type of Microscope, of which it should not require the alteration or 

 special adaptation of any part, nor interfere with its use as an 

 ordinary instrument when required. 



The device now described (fig. 82) fulfils these conditions in 

 a manner that promises complete success. 



The construction is based upon the fact that if an objective 

 be placed at right angles to the axis of a Microscope, any rays 

 of light passing through it may be deflected up the tube to the 

 ocular by means of a mirror placed at a suitable angle, and that 

 any object in the focus of the secondary objective will be seen 

 simultaneously with the image produced by the direct rays from 

 the primary objective. 



Two images will thus be transmitted to the ocular, and appear 

 superimposed upon each other, and consequently blurred. 



