54 



THE AMERICAN MONTHLY 



[March, 



there is a flood of light from it, which 

 is detrimental to good resolution. 



A New Form of Vertical Illu- 

 minator. — A proposoi the article we 

 print this month, it may be well to 

 once more call attention to the inge- 

 nious device of Prof. W. A. Rogers 

 (we believe it was invented by him), 

 made by Mr. Tolles. We refer to the 

 reflecting prism fitted ihto the object- 

 ive just back of the front lens. By 

 throwing light upon the exposed face 

 of the prism, it is reflected down 

 through the front lens upon the ob- 

 ject, and certainly gives a most excel- 

 lent illumination. Prof. Rogers has 

 used it in the examination of his ruled 

 plates with great satisfaction. A 

 member of the New York Microsco- 

 pical Society, Mr. James Warnock, has 

 recently received from Mr. Tolles, a 

 -J-inch objective of large aperture, 

 with this attachment, which gives a 

 fine definition of the lines on Amphi- 

 pleura pellucida. Before long we in- 

 tend to allude to this subject again, 

 and to give an account of a compari- 

 son between this and the common 

 vertical illuminator. 



Meanwhile, we wish to suggest 

 another form for a vertical illmin- 

 ator, which, it seems to us, might 

 prove to be better than the ordina- 

 ry one, and certainly more conve- 

 nient for use. It was first de- 

 scribed at the meeting of the New 

 York Microscopical Society, held 

 March 3d. Instead of the reflector 

 now used, we suggest a small glass re- 

 flecting prism to be placed in the 

 nose-piece in the same way and in the 

 same position as the Wenham binocu- 

 lar-prism, and in the case of binocu- 

 lar microscopes it should replace the 

 latter. The back surface of the prism, 

 which receives the light, may be 

 either plane or curved — it might be 

 found advisable to make this surface 

 act as a lens to throw the light upon 

 the back of the objective in the most 

 advantageous manner for illumina- 

 tion. All parts of the prism not used 

 should be blackened, so that no light 



except what passes down to the ob- 

 jective can enter the tube. A rotat- 

 ing diaphragm can be added, working 

 in front of the exposed surface of the 

 prism ; but this would probably be 

 an unnecessary expense. 

 o 



About Stands. — The articles we 

 have lately published about stands 

 have aroused considerable interest in 

 various quarters. The Editors of the 

 Botanical Gazette have shown their 

 full appreciation of the importance of 

 the subject by asking: " Does it follow 

 that if such work can be done by or- 

 dinary instruments, even more as- 

 tonishing results can be obtained by 

 using finer ones ? Or, is it a fact that 

 the extra appliances, etc., are more 

 things of 'fuss and feather' than 

 fruitful additions to biological labora- 

 tories ?" 



The first question we have answer- 

 ed clearly enough. The second de- 

 serves a little more attention. Some 

 accessories are certainly important, 

 but there is a long list of them which 

 embraces many that are quite useless 

 for purposes of investigation, and 

 very many others that are mere con- 

 veniences — good articles to have if 

 one can well afford them, but which 

 are not required. 



It would, perhaps, surprise many 

 novices to learn how very few of the 

 accessories in our catalogues are of 

 great practical utility for purposes of 

 investigation. These few, however, 

 are almost indispensable for some 

 kinds of work; therefore, we have ad- 

 vised the purchase of microscopes 

 with substages in every case. 

 o 



New Sponges. — In the Proceedings 

 of the Academy of Natural Sciences^ 

 of Philadelphia, Mr. Edw. Potts has 

 two short notes about fresh-water 

 sponges. He considers that the 

 characteristics of the statospheres and 

 their spicules furnish the only reli- 

 able distinctions between the fresh- 

 water sponges. Some American 

 forms differ from the typical English 

 species, both in the shape of the spi- 



