206 



THE AMEKICAN MONTHLY 



[November, 



thereto. The diagram renders fur- 

 ther description superfluous. 



Though the result will be the same 

 if the prism is either above or below 

 the slide, it is better to have it above 

 as there is then no danger of letting 

 any light pass outside of it, and en- 

 tering the slide at less than the angle 

 of total reflection. To make this 

 device still cheaper, the prism may 

 be dispensed with and a small drop 

 of glycerin, balsam or other highly 

 refractive fluid put in its place. 



Only dry-objectives can be used 

 with this illumination, for the stra- 

 tum of fluid, of an immersion lens 

 would prevent reflection from the 

 upper surface of the covering- 

 glass. 



I have used this method with 

 magnifying powers of four thou- 

 sand diameters — having plenty of 

 light and good deflnition. I do not 

 mean to claim that this is equal 

 to the more expensive methods — 

 such as the vertical illuminator, etc., 

 but still it is of use at times and is 

 exceedingly economical. It may 

 not be new, but I have never heard 

 of its having been in use before. 



On Mounting and Staining 

 Pollen. 



At a recent meeting of the New 

 York Microscopical Society, Dr. 

 W. H. Bates, of Brooklyn, exhibited 

 some of the most beautiful slides of 

 stained pollen. They were prepared 

 by the Rev. J. T. Bi'ownell, and 

 the process was described as fol- 

 lows : — 



1. Place a small quantity of pollen 

 on the centre of the slide. 



2. Place a small drop of staining 

 fluid (anilin dissolved in alcohol) 

 upon the pollen. 



3. Wash, by dropping on pure 

 alcohol until all trace of sediment, 

 or of stains upon the glass among 



the pollen grains, and washed away. 



4. Wipe clean with a dry cloth 

 drawn over the end of a pointed 

 stick, turning the slide rapidly on 

 the turn-table. 



5. When thus cleaned and quite 

 dry, put on a drop of spirit of tur- 

 pentine. 



H. Put on the balsam, and cover.. 



A few kinds of pollen are dis- 

 torted by the action of alcohol. 

 Some of these can be stained by 

 the use of an ammoniated solution 

 of anilin. Those that will not bear 

 this solution may be mounted un- 

 stained, beginning at process 5. 

 The slides that were shown bore 

 evidence that Mr. Brown ell is one 

 of the neatest and most tasteful of 

 mounters. 



Concerning Eye-pieces. 



It is well known that the magni- 

 fying power of the eye-pieces made 

 for the microscope by difi^erent 

 makers varies considerably. Some 

 time ago Mr. W. H. Bulloch, of 

 Chicago, sent a series of measure- 

 ments of eye-pieces to the Editor of 

 this Journal. The results are given 

 below. The rule which Mr. Bulloch 

 followed for determining the focal 

 length of the eye-pieces may be 

 stated as follows : Multiply the 

 focal length of the eye-lens and field- 

 lens together and divide the product 

 hy the distance hetioee7i the lenses 

 {which is half the sum of their 

 focal lengths). 



Example : AVhat is the focal 

 length of an eye-piece, the field-leas 

 of which has a focus of 2.5 and the 

 eye-lens a focus of 1.25 inchs? Cal- 

 culate as follows : 2.5xl.25=:8.125. 

 2.5 + 1.25=3.75 and 3.75-^2=1.87 

 (distance between the lenses). 3.125 

 H- 1.87 = 1.67 which is the focal 

 length required. 



In the s,ummary of results given 

 below the eye-pieces of the ' same 



