ii8 



THE AMERICAN MONTHLY 



[June, 



We have no doubt that some such 

 method will be universally adopted by 

 chemists in the near future. Already 

 we learn from Prof. A. R. Leeds, who 

 has been actively engaged in the anal- 

 ysis of waters for several years, that 

 he has tried the process in his inves- 

 tigations, but with what success we are 

 not informed. 



It is said that occasionally there 

 form in the gelatin, clear, spherical 

 vesicles, from which a fluid may be 

 withdrawn by a pipette. The bottom 

 of such vesicles contains active bac- 

 teria. 



Apparatus for Photo-Microgra- 

 phy. — Mr. George Smith describes 

 an ingenious arrangement for photo- 

 graphing microscopic objects without 

 an expensive camera, in the British 

 Journal of Photography. He uses for 

 a camera two boxes with sliding lids 

 about fifteen inches long and five in- 

 ches square. The ends of both boxes 

 are knocked out and a sheet of heavy 

 brown card-board is folded so as to fit 

 the inside of the wooden boxes quite 

 loosely, the two edges overlapping at 

 the bottom. By inserting one end of 

 this tube into each wooden box the 

 sliding camera is complete. The in- 

 side is thoroughly blackened by veg- 

 etable black made into a thick paste 

 with spirit varnish and then diluted 

 with alcohol. 



A board is then chosen the full 

 length of the camera when extended, 

 that is, as long as the two boxes and 

 the connecting tubes together. The 

 box which is to carrv the optical 

 apparatus is screwed down to one end 

 of the board. The other box slides be- 

 tween two wooden guides, so that the 

 camera can be shortened or lengthened 

 at will, to increase or diminish the 

 magnifying power. A cloth thrown 

 over the arrangement keeps out the 

 light perfectly. 



The objective is mounted in the 

 front box in a manner rather difficult 

 to explain without a diagram, but we 

 believe this can be left to the inge- 

 nuity of the reader, merely saying 



that Mr. Smith fits the tube of a brass 

 objective-box so as to slide in another 

 tube lined with cloth. The bottom 

 of the box is knocked out, and a 

 society screw cut in the cover to hold 

 the objective. 



The sensitive plate, and also the 

 ground glass for focussing are ar- 

 ranged at the back of the box at the 

 other end in a convenient way, such 

 as any person can devise. 



The simplicity and cheapness of 

 this arrangement will doubtless com- 

 mend it to many of our readers. There 

 should be some means of focussing 

 the objective while the operator is 

 looking at the image. This can be 

 done by sliding the box out or in as 

 required, but a far better plan is by 

 means of a rod reaching to the front 

 having a cord passing over a pulley 

 moving a screw-adjustment for the 

 objective. 



Plates 3^ by 4^ inches square are 

 a convenient and useful size, but 

 larger ones are often desirable. A 

 common size is 4 by 5 inches. 



NOTES. 



— Prof. S. A. Forbes has been experi- 

 menting on amphipleura pell^icidai and 

 he announces that he has obtained perfect 

 resolution of that test in balsam, with a 

 -^^ inch objective by Spencer, under re- 

 markable circumstances. He writes : 

 " My arrangements are the simplest pos- 

 sible, — a Bulloch '■biologicar stand with 

 the concave mirror, and any eye-piece 

 from a 2-inch to a |-inch. The light is 

 that just outside of the disk of dazzling 

 brilliance derived from sunlight. It makes 

 no difference whether the mirror is strictly 

 central, or whether it be swung laterally 

 until that margin is central of it from 

 which the rays used actually come, i.e., 

 about io°." In a later communication 

 Prof. Forbes suggests that there may be 

 some unknown reflections which produce 

 this result, for while the resolution is per- 

 fect when the diatom lies transverse to 

 the stage, they disappear as the direction 

 is changed. The resolution is excellent 

 with the mirror entirely darkened, except 

 at a spot only 4 mm. (about ^^ of an inch) 

 in diameter. 



