ZOOLOGY AND BOTANY, MICEOSCOPYj ETC. 711 



dating from about 1750. A second is in the form of a square turret 

 of wood with an opening in front for light to reach the mirror within, 

 and two lateral slits for the insertion of the slide. In the upper end 

 is a double (sliding) tube of wood and paper carrying the objective 

 and eye-piece. It was probably made in Nuremberg in the last century. 

 The other four have no special history, and date from 1817 (then 

 bought of Voigtlander for the Vienna University), 1811-20 ? (by 

 [Jtzschneider, Eeichenbach, and Fraunhofer), 1820-6 (Utzschneider 

 and Fraunhofer), and probably before 1830 (Chevallier). 



Standard Eye-pieces.* — Dr. Blackham, on behalf of the committee 

 on Eye-pieces, presented the following report to the Chicago Meeting 

 of the American Society of Microscopists : " Your committee on 

 nomenclature and sizes of oculars would unanimously report : — 



1. In favour of naming oculars, like objectives, by their equivalent 

 focal lengths in English inches. We believe this method to be the 

 best adapted to practical use, sufficiently precise for its object, and 

 capable of general introduction with less inconvenience, opposition, or 

 delay than any other rational system. Assuming that 1 in. indi- 

 cates an amplification of ten diameters, 5 in. of two diameters, 

 l-5th in. of fifty diameters, &c., as actually obtained by a com- 

 pound Microscope with a 10 in. tube (from the diaphragm of the 

 ocular to the front lens of the objective), the image being measured by 

 the camera lucida at a distance of ten inches from the camera, and that 

 the amplifying power in use can be approximately determined by mul- 

 tiplying together the powers thus implied in the names of the objective 

 and ocular, an extremely simple and comprehensive system is ob- 

 tained, whose practical benefits are believed to greatly exceed its 

 technical or theoretical faults, and whose adoption would add much to 

 the definiteness and intelligence of the microscopical work. A table 

 showing the simplicity and scope of this system is given in the Journal 

 of the Eoyal Microscopical Society for 1882, page 105. 



2. In favour of adopting one or more standard sizes for the tubes 

 of oculars. That uniformity in this respect would be a great con- 

 venience to students, and, to say the least, no disadvantage to manu- 

 facturers, we do not doubt ; but the difficulties in the way of adopting 

 such a policy at the present time are evidently great, far beyond com- 

 parison with those encountered in the introduction of the ' Society 

 screw.' Furthermore, the great variety of tastes among both makers 

 and buyers as to sizes, styles, and pieces of stands seems to call for 

 not less than two or three standard diameters of tube. As an im- 

 portant step toward uniformity we would gladly recommend the 

 adoption of the sizes recently proposed by the Eoyal Microscopical 

 Society, 0-92 and 1-35 in., were they adapted to the conditions 

 existing in this country. But 0-92 is a smaller size than we are 

 willing to recommend for any purpose, being much too little, in our 

 judgment, for even the small, compact stands of the 'Continental' 

 model. On the other hand, we would have preferred 1 • 40 for the 



* ' Chicago Times,' 9th August, 1883, in advance of Proc. Amor. Soc. Micr., 

 6th Ann. Meeting, 3883. 



