174: THE AMERICAN MONTHLY [June, 



tides were thus caught in the meshes of the muslin, from which 

 they were afterwards easily washed by shaking the cloth in a 

 shallow dish of water. The bare magnet was then moved about in 

 the dish of water, and the particles thus collected transferred to a 

 glass slip and mounted. A comparison with similar particles 

 obtained from coal-ashes presented scarcely any difference. 



In this connection it may be of interest to add that I have ex- 

 amined hail but failed to find magnetic particles, though the dust 

 found in the hail was considerable. Has anybody ever gathered 

 such magnetic spherules from hail.^ 



E. B. Knerr. 



Atchison, Kansas, April 24^ 1^93- 



(30) Criticism of Wethered's Medical Microscopy. — On 



page 153 Wethered states that fresh material frozen and sectioned 

 can be used for temporary examination, but that if you want per- 

 manent mounts the material must be hardened, embedded and 

 sectioned. 



But I have many sections that were never hardened nor em- 

 bedded, which, thovigh mounted years ago, are as good as they 

 ever were. They were frozen and sectioned with Cathcart's 

 microtome, then stained and mounted without having been sec- 

 tioned, hardened or embedded. The beautiful sections of Arthur 

 Cole are made by freezing with Cathcart's microtome and without 

 embedding. 



On page 321 Wethered says that the red corpuscles are i-3200th 

 inch in diameter, but he should have added that thev vary in size 

 both above and below that fisrure. P. C. C. 



MICROSCOPICAL APPARATUS. 



A Cheap Microscope Illuminator. — Take any flat-wick lamp 

 with a good burner and a clear, clean chimney. Light the lamp, 

 put on the chimney, turn up the wick a little, and with a card 

 check the draught by partly covering the opening at the upper 

 end of the chimney. This will smoke the inside of the chimney 

 and make it impervious to light ; or light the lamp without the 

 chimney, turn up the wick until it smokes freely, and smoke the 

 inside of the chimney until it will not show any light through the 

 blackened surface ; allow the chimney to cool, and with a piece of 

 paper remove the soot from a small part of the inside opposite 

 the brightest part of the flame. The clear spot can be placed 

 towards the edge or side of the flame as wanted. 



Providence, R. I. N. N. Mason. 



The Acme Lamp and Attachments, — The lamp consists of 

 a heavy base with upright, carrying a claw-shaped holder, adjust- 

 able vertically and also turning on a horizontal axis. This claw- 



