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THE AMERICAN MONTHLY 



i 



[November^ 



The smallness of field can easily be 

 "connected by making the eye-pieces 

 of the English pattern, and when this 

 is done it will be superior to the Wen- 

 ham method every way. The light is 

 not appreciably less than in the ordi- 

 nary binocular. It is certainly abun- 

 dant. 



You will understand, then, how I 

 am naturally feeling that my little 

 Zentmayer is now very nearly a model 

 stand. J. D. Cox. 



Cincinnati, Oct. 14th, 1881. 



Achromatic Illumination for 

 Low Powers. 



My highest objective at present is 

 a Tolles ^-inch, and I am conse- 

 quently obliged to use high oculars 

 to obtain great amplification when 

 desirable. My -^ has an aperture of 

 100°, yet even with this tolerably 

 wide angle, there is necessarily a con- 

 siderable loss of light when the solid 

 eye-pieces are used. To remedy this, 

 I some time ago applied to Messrs. 

 Queen & Co., of Philadelphia, to fur- 

 nish me with a Kelner " C " eye-piece, 

 fitted with an adapter for my sub- 

 stage, to serve as an achromatic con- 

 denser, the form so highly spoken of by 

 Dr. Beale. The condenser came in 

 due time, and after a thorough trial I 

 am very much pleased with it indeed. 

 It is only suitable for central light 

 work, there being no diaphragm as in 

 its prototype, the Webster condenser. 

 By lamp-light, using the quarter-inch 

 solid ocular, it gives with the ^, a 

 clear, brightly illuminated -field, as 

 bright as that given by the two-inch 

 ocular when the condenser is removed. 

 The light needs to be diminished a 

 little when using the half-inch solid 

 ocular, which is done by turning down 

 the wick of the lamp. The bright, 

 achromatic light, which seems to bring 

 out details of structure with a distinct- 

 ness such as I can secure by no other 

 means, being superior to the best re- 

 sults obtained by condensing the light 

 on the mirror with a large bull's-eye. 

 There is a marked decrease of that 



watery, hazy appearance, generally 

 noticeable when even the best object- 

 ives are " strained up " by high ocu- 

 lars. Using the ^ and the quarter- 

 inch solid ocular on a medium scale 

 of Z. curvicollis, while the definition 

 of the edges of the " exclamation 

 marks" is, of course, less sharp and 

 clean than with the half-inch or lower 

 oculars, yet the result is remarkably 

 good, and the effect is attributable, 

 in a great measure, I am sure, to the 

 character of the light employed. And 

 it is not alone on test-objects that the 

 condenser works well. Upon any ob- 

 ject suitable for study with high pow- 

 ers, there is an unmistakable advan 

 tage secured by this mode of ilium 

 nation. 



Messrs. Queen & Co.'s bill for tK 

 condenser, including sub-stage adapt- 

 er and three caps with different 

 sized openings, was $8.50, which is 

 considerably less than the price of 

 the Webster condenser, which, I be- 

 lieve, is the cheapest form of the 

 regular achromatic condenser made. 

 And I am of the opinion that when I 

 am the possessor of a still higher 

 power objective, my " Kelner " will 

 still stand ready to help that to do its 

 best work as readily as it does my 

 Tolles <^ now. 



A. L. Woodward. 



1™' 



Note on the Functions of the 

 Spinal Cord in the Frog. 



BY E. A. BIRGE, PH. D., 



Professor of Zo»logy^ University of Missouri. 



The experiments described in the 

 following paragraphs were carried out 

 in the spring of the year 1881, at the 

 suggestion and' under the direction of 

 Professor Ludwig, in the Phrenologi- 

 cal Laboratory of the University of 

 Leipzig. The point to be studied and 

 the methods of work were sug- 

 gested by Prof. Ludwig, and I am 

 responsible only for carrying out his 

 plans. The work was in continuation 

 of an anatomical investigation which 



