234 
POPULAR SCIENCE REVIEW. 
the above subject. It will be found in the Philosophical Magazine for 
January. 
Standard Thermometers. — Perhaps there is no instrument which it is of 
more importance to the meteorologist to have perfectly corrected than the 
thermometer ; yet we learn, from a letter recently addressed to the Times , 
by Mr. H. 0. Kay, that even among the instruments of the first London 
makers there is a great want of uniformity. A correspondent of the Chemical 
News, writing upon the same subject, corroborates Mr. Kay’s remarks. 
Two years ago, he required a first-class maximum registering thermometer 
for scientific purposes, and he applied to Messrs. Negretti and Zambra for a 
standard instrument, with the Kew certificate. Not having one of them at 
the time, they sent him one of the instruments with Mr. Glaisher’s certifi- 
cate, which stated that the u reading ” was 05° too high throughout the 
range. Some time after, suspecting that the difference was greater than 
was represented, he made a comparison with some of the Kew certificated 
instruments, and found the following result : — 
Kew instrument, 
degrees. 
574 
704 
79 
Mr. Grlaisher’s instrument, 
degrees. 
59 
72 
. . 81* 
We draw attention to these facts, because they are of serious importance. 
We trust, therefore, that some arrangements may be come to by which only 
one certificate shall be allowed, and which shall compel all standard ther- 
mometers to be registered. 
Vapour Density. — There is now being given a good deal of attention to 
this subject, especially upon the Continent. M. Deville, who, as well as 
M. Cahours, has given it especial consideration, considers that the objections 
which many chemists have to admit that the equivalents of elements and 
compounds correspond to one and eight volumes, being grounded on ana- 
logies, are supported by little better than gratuitous hypotheses. He has, 
in conjunction with Troost, taken the vapour density of NH 4 I,HgI at 350° 
and 440°, and obtained the numbers 6 - 49 and 6‘38, the density calculated 
for eight volumes being 6-44. 
ZOOLOGY AND COMPAEATIYE ANATOMY. 
A new Rotifer. — The Microscopical Journal, in its analysis of foreign me- 
moirs, often supplies us with valuable and interesting information. Not the 
least important of the matters recorded in its last chronicle is that which 
refers to the discovery and description of a new rotifer by Herr Elias Mecz- 
nikow. This observer states that when examining the under surface of some 
leaves of the Nymphcea lutea at Giessen he discovered a number of white 
lenticular bodies, which proved on examination to be forms of a new species 
of rotifer. The adult form of this remarkable species appears when expanded 
to consist of two nearly equal circular sacs, the anterior of which is open, 
forming the mouth, and is destitute of any wheel apparatus ; it possesses at 
