The Microscope. 25 



chagrin, that, as mentioned on another page, M. Albert Brun, 

 the professor of chemistrj'' in the University of Geneva, has dis- 

 covered a method of making opal of such a character that it 

 may be used instead of the untrustworthy fluor-spar for the 

 making of apochromatic objectives. Diamonds have been arti- 

 ficially made by a very expensive and laborious chemical pro- 

 cess, but opal making appears to belong to another category, 

 and to be be3^ond a peradventure. 



At first glance the discovery seems to be for the advantage of 

 microscopists in general, but those that have read of the fluor- 

 spar expose will recollect that Zeiss has practically^ a monopoly 

 of all the optically available flourite of the world. It is there- 

 fore impossible for other opticians to make actual apochromatics 

 It remains equall}^ impossible for any optician, except Zeiss, to 

 use the newly discovered, artificial opal, since he has acquired 

 both the process of manufacture and the sole right to use the 

 material. Any hope that may have glimmered along the micro- 

 scopist's mental horizon that American or British opticians 

 might make apochromatic objectives with opal lenses amongst 

 the glass, must flash out into the darkness of disappointment. 

 Those that might want an opal apochromatic objective must 

 probably pay, as they have paid for the fluorite lenses, almost its 

 weight in hard earned gold. Yet there is one satisfaction. No 

 opal apochromaiic has j^et been made. It is known onl}^ that the 

 artificial material can be used, that it can be prepared in suffi. 

 cient quantity and of the proper size, and that it possesses all 

 the good qualities of fluor-spar with none of its softness, its 

 obnoxious, exfoliating and pitting ability, and with none of its 

 rarity as an optically available mineral. What an opal objective 

 may do or not do, no one can guess. It may do nothing good. 

 Let us comfort ourselves with that improbable conjecture. It 

 may be superior to the apochromatics. In that case — well, in 

 that case, perhaps the fluorite objectives may be a little cheaper, 

 or may be made in this country, and the American ones may 

 not pit and scale off in little flakes ; perhaps — but what a queer 

 thing the imagination is, to be sure ! 



Acknowledgment. — To Mr. F. Dienelt, Loda, 111., for three 

 slides of the anatomy of the honey bee. These are the result of 

 much careful dissection, work in which Mr. Dienelt is expert. — 



