802 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The advantage claimed for this form is its inexpensive addition to 

 what is ordinarily part of the apparatus of the microscopist. It can 

 be used as an ordinary or immersion condenser, and when employed 

 for photo-micrography, on looking along the path of the illumination 

 from behind, a ring of light is observed round the edge of the field 

 lens, equally divided by a narrow vertical image of the flame, if all 

 the parts be correctly centered. 



Osborne's Diatomescope.* — Lord S. G. Osborne calls attention 

 to a little instrument he has invented, which he thinks " may, 

 when once known, be of great service to those observers who, like 

 myself, take great interest in the study of the beautiful forms found 

 in the diatom class of objects. 



I have now, for a very long time, worked patiently in an endeavour 

 to procure the means of viewing these objects by oblique light. I 

 possess many of the modern inventions for the purpose ; with all I 

 could get much good result ; but I yet failed with them to arrive at 

 my chief aim — ^to possess means of a simple character, easy to use, 

 capable of being put into the market at small cost, which should give 

 with all powers, from 1 in. to 1/4 in., a perfectly black background, 

 the objects under observation brilliantly illuminated. 



I have now done this, and the rough models made by my own hands 

 have been seen in use by some well-skilled observers, who have all 

 admitted that my purpose has been fully achieved. 



It was my first intention to have simply published in your 

 columns the formula for the construction of the instrument ; but 

 having had to make a great many with my own hands, experience 

 taught me that it would be far better to employ skilled labour to act 

 in the first instance under my own supervision to secure accuracy, 

 than to risk the disappointment in the case of those who, wanting 

 my practical experience, might well fail to get all the nicety of 

 adjustment necessary for success. 



I therefore have gladly availed myself of the offer of Mr. Ernest 

 Hinton, who has had much experience in connection with the mount- 

 ing of diatoms, to aid me in getting the little apparatus accurately 

 made. ... 



The instrument is applicable to the stage of any stand which has 

 the usual lateral and vertical movements, and if there is a clamp to 

 keep the slides in situ, nothing more is wanted ; failing the existence 

 of a clamp, two small pegs fixed to the instrument to drop into two 

 holes in the sides of the stage will answer equally well. If, as in 

 some of the small stands, the aperture in the stage is circular, no 

 clamp is necessary, as the instrument can be set in a piece of tubing 

 to drop into this, with a narrow thin flange to prevent its falling 

 through. 



In whatever way it is applied to the stage, the method of use is 

 very simple. The stage beiug set central, the diatomescope is either 

 laid on it, or, as above, dropped into it. It is well to have a pilot 

 slide. I always use the ' Orthosiren.' Place this in the springs, 



* Engl. Mecli., xxxix. (1884) p. 561. 



