SCIENTIFIC SUMMARY. 
331 
A Lecture Experiment demonstrating the Expansion of Water is thus de- 
scribed by Herr F. Riidorff. In order to exhibit the effect of the expansion 
of water when freezing, the author tills with distilled and previously well- 
boiled and cooled water, a cast-iron cylinder having the following dimen- 
sions : — Height, 160 mm. ; diameter (external), 50 mm. ; thickness of solid 
iron, 15 mm. After having been filled with water, this apparatus is closed 
by means of a plug screwed into the neck, and the cylinder is next placed 
in a mixture of three parts of snow or pounded ice, and one part of common 
salt ; after about forty minutes the cylinder bursts with a loud report. It is 
essential for the success of this experiment that the plug fits very per- 
fectly, and that the cylinder, after having been filled with water, be placed 
for some time in ice. The wooden pail which contains the cooling mix- 
ture should be rather roomy, and be covered with a stout towel to prevent 
the spirting about of the contents at the time of the bursting. — Berichte der 
deutsch. Chem. GeseU., No. 2, 1870. 
Cement for Glass Prisms. — We have received so many letters of inquiry 
on this subject that we publish the following extract from the Scientific 
American of June 4 : — The best cement for putting together glass prisms, to be 
filled with carbon disulphide (bisulphide of carbon), is a mixture of com- 
mon glue and West India molasses. Make a tolerably liquid glue, and add 
about one eighth the quantity of common molasses. Lay the metal or glass 
form, ground to a suitable angle, with its face up : then place the glass plate 
upon it, and apply the cement on the under side with a brush, and allow it 
to flow by capillary attraction between the glass and the form : repeat this 
operation several times if necessary. This is better than to wet the edge of 
the glass at the outset before attaching it to the prism. The stopper to the 
prism can be cemented in the same way, and in filling with the carbon 
disulphide, always leave a small space for the expansion of the liquid. 
The prisms want to be kept in a cool, dark place, and ought not to be 
agitated previous to using, as the light is in that case unequally re- 
fracted. 
A Peculiar Telegraphic Improvement. — The (American) Telegrapher 
describes a valuable improvement in relay magnets, by W. W. Smith, of 
Cincinnati, Ohio. The improvement consists in arranging the connections 
of a relay so that the main circuit is divided, one half passing through each 
helix, and uniting again on the opposite side, instead of having the conduct- 
ing wire of the two spools continuous, as in the usual manner. It will be 
seen upon a moment’s reflection that, by changing the connections of a 
magnet of the usual form, and arranging them upon Mr. Smith’s plan, 
the total resistance will be reduced one-fourth of the original amount, while 
the two helices will exert their magnetic influence in conjunction upon the 
soft iron cores, as usual. 
ZOOLOGY AND COMPARATIVE ANATOMY. 
A Peculiar Specimen of Hyalonema. — Of the specimens of Hyalonema in 
the Museum of the Academy of Natural Sciences of Philadelphia there is 
one, according to Professor Joseph Leidy, which appears to him to be 
