Tue Microscope. . 115 
been made. For photo-micrography a third eye-piece magnify- 
ing 24 times is supplied, the lenses of which can be slightly sep- ° 
arated for exact adjustment of the image. 
Two series of objectives will be constructed, one adapted 
for the short Continental body-tube and the other for the long 
English body-tube, and there will be acorresponding “ compen- 
sating”’ series of eye-pieces. The homogeneous-immersion lenses 
will have apertures of 1.40 N.A. and 1.30 N.A., and focal length 
of 3.0 mm. and 2.0 mm., the latter with much increased working 
distance. The water-immersion lenses will have an aperture of 
1.25 N.A. and a focal length of 2.5 mm., and the dry lenses 0.95 
N.A., 0.60 N.A., and 0.30 N.A., with focal lengths of 4 mm., 8 
mm., and 16 mm. 
We append what will we think be of interest to many or 
the Fellows, a brief account of what we understand to be the 
history of the construction of the new glass, though, as we have 
not been able to submit it to Prof. Abbe, he must not be under- 
stood to endorse it in any way. 
The origin of the matter was Prof. Abbe’s Report on the 
Microscopes of the South Kensington Exhibition published in 
1878. This contained at the end some general considerations as 
to the unfulfilled requirements of practical optics in regard to 
the properties of optical glass, and complaints of the unfavour- 
able conditions then existing. Dr. O. Schott (of Witten, in 
Westphalia), a chemist, but long versed in practical glass-mak- 
ing, and who had made some remarkable researches on the 
physical properties of glass, read the report, and in the begin- 
ning of 1881, having communicated with Prof. Abbe, they com- 
mensed a preliminary study of the optical properties of the 
various chemical elements as far as they admit of “ vitrificable ” 
combinations. This was conducted at first on a very small scale, 
Dr. Schott working alone at Witten, and the optical parts of the 
research being carried out at Jena. After a year it was decided 
to continue the experiments on a larger scale, with the object 
not only to determine the optical effects of various elements, 
but to try the production of practically useful combinations. In 
January 1882, Dr. Schott settled at Jena, and he and Prof. Abbe 
established a complete melting-laboratory with large gas-furna- 
ces, a gas engine for driving blowers, etc., and with the aid of 
