382 
POPULAR SCIENCE REVIEW. 
a considerable stock on band, we invite tbe attention of microscopists to such 
specimens as we have examined. 
Improvements in Objectives . — In his address to the Microscopical Society, 
Mr. Grlaisher pointed out the recent improvement in this direction, viz., the 
application of the single-front lens to the highest powers, in place of the triple 
combination usually employed by the different makers. A simple anterior 
lens transmits more light, gives clearer definition, with any desired extent of 
aperture, and, from its simplicity and comparative freedom from errors of 
workmanship, is worthy of recommendation. The chromatic and spherical 
aberrations may be perfectly corrected in this form. Mr. Wenham informed 
Mr. Glaisher that there are now object-glasses existing, of various powers, 
having only a single-front lens, that will challenge comparison with the best of 
the usual form. It is suggested by Mr. Wenham, who has made practical 
investigations in the optical branch of Microscopy, that further improve- 
ments may be anticipated in the performance of object-glasses by discoveries 
connected with the quality of the glass employed. — Vide reprint of Presi- 
dent’s Address. 
PAPERS ON HISTOLOGY. 
Botany. — The Colouring-matter of Sea- weeds. 
Movements of the Diatomaceae. 
The Aeriferous Roots of Jussisea. 
The Seeds of Solanacese. 
Medicine. — The Cause of Ague. 
Nitrate of Silver in Microscopy. 
Perivascular Canals in the Brain. 
Zoology. — Fresh-water Polyzoa. 
The Fish’s Eye. 
PHOTOGRAPHY. 
A most Important Discovery . — That photographic productions cannot be 
relied upon as permanent, appears a fact only too well established. The 
public have been convinced of it by seeing folios of choice productions and 
scores of treasured portraits pass gradually into “the sear and yellow leaf” of 
their age, and finally disappear. A few years, more or less, generally works 
the change. Photographers, too, have lost all faith in the absolute permanence 
of their productions, and have long been looking for this desirable quality in 
s ome ideal process for which their experimentalists were industriously striving 
and working, and for which they were most anxiously looking, rather than to 
