Journal of Microscopical Science. 65 



placed on the rnicroscope stage (k), so that the flat side is upper- 

 most, upon which is placed the ohject to be examined. The rays 

 are brought to a focus (f), at some distance above the object (o), 

 thus giving an even -vhite light over the whole field of vision, and 

 this I have found particularly advantageous when using low powers 

 for viewing objects. We can modify this arrangement by placing 

 the lens below the stage, (as in fig. 2), and at a point where it can 

 be adjusted by a rack and pinion, so that the rays from it are fo- 

 cussed on the object However, the first arrangement I have 

 found the most generally useful. To this can be added a diaphragm 

 (fig. 3), which any one can make for himself, to fit the microscope, 

 of blackened card-board. The general utility and cheapness of 

 this simple contrivance will, I think, recommend it to the consi- 

 deration of all whose purses are not as large as their drcJire for 

 knowledge. 



Fig. 3. 



I should also mention that I have found this illuminator parti- 

 cularly useful on dull days, when, by the mirror alone, only a gray 

 light could be obtained, while with the addition of my condensing 

 lens a clear white light is obtained, and from the reason of most 

 of the rays falling obliquely on the object, the markings of certain 

 of the Diatomacese can be easily resolved with it. When the dia- 

 phragm (fig. 3) is added, with its numerous apertures, and which 

 can be varied to suit the fancy, we get an apparatus which, on 

 important occasions, will be found to fill the place of the more 

 expensive achromatic condenser. 



K Arthur M. Edwards, New Yorh. 



