224 The Microscope. 



either straight or curved, the smallest, called an eye dropper, de- 

 livering about one fourth of a minim ; the larger is a medicine 

 dropper and delivers one minim at a drop ; they fit into a one 

 or two ounce bottle, and as they hang straight in it are never 

 clogged at the point and can be reinserted in the vial after each 

 using easier than a common reagent tube can be laid down. 

 They are cheap, always ready and, fitting tightly, keep out dust 

 and prevent evaporation. 



The making of cells involves considerable trouble and time 

 to those who only occasionally use the microscope ; why are 

 there no slides on sale that have the cell ground in the glass? We 

 have slides with a concave cell ground in them, why not have 

 cells with their sides perpendicular to the base? It does not 

 seem as though it would be very much of a mechanical triumph 

 to do so, when this bother of cell making would be banished. 

 Machinery should make cells of all sizes and depths cheaper 

 than the hand. 



Boulder, Col. Chas. A mbrook, m. d. 



Editor The Microscope : — 



Respecting the " polarizing with one Nicol," there is something 

 better, at all events easier than the use of the sky, and that is. 

 any glazed surface, except of metals (even a dish of water will 

 do very well), all of which can polarize the light ; the darker 

 the color the better. In order to make use of it, merely turn 

 aside the mirror and take the " sheen " from your mahogany 

 table, for instance. Daylight is sufficient, although sunlight 

 gives more brilliant effects. This is not original with me, but 

 will be found in many text books of physics. 



Philadelphia. Hans M. Wilder. 



Editor The Microscope : — 



A short time ago I ordered of Prof M. D. Ewell, of Chicago^ 

 a stage micrometer ruled 1, ^ and j^o mm. 



I submitted this micrometer to a most thorough examination,, 

 examining and re-examining line for line for the purpose of de- 

 termining any possible variation in the rulings. 



The variation in the width of the spaces is too small to esti- 

 mate ; the error therefore is an insensible one. 



A Spencer ^ H. I. objective was used for testing this slide^ 

 which I consider a most excellent micrometer. 



Buffalo, N. Y. John A. Miller. Ph. D. 



