388 
POPULAR SCIENCE REVIEW. 
from 7° or 8° to 18° or 20° above zero. When the mercury rises above 20°, 
however suddenly, the ice disappears. The greatest collection, it has been 
observed, occurs at night, and when the sun is obscured by clouds ; but, 
when the sun is unclouded, no difficulty is ever experienced. The observa- 
tions do not state the effects of a cloudless night. — Vide The Reader. 
The Electricities of Iron and Steel. — The doctrines of our British physicist, 
Dr. J oule, relative to the electricities of cast-iron and steel, have been quite 
corroborated by the researches of M. Thenard. The French chemist was not 
aware of Dr. Joule’s investigations till he came to publish his own, but then 
he acknowledged their priority in a graceful manner. 
New Method of producing Ice. — Signor Tonelli has constructed an ice-making 
machine which is intended for household purposes, in which compressed steam 
replaces the ammonia or sulphurous acid gas used in the ordinary machines. 
One of his small machines will make from 9 to 11 lbs. of ice per hour at a cost 
of i|d. to |d. a pound. The plan adopted is briefly as follows : — In one 
cylinder a solution of common salt is placed, and to this another cylinder is 
adapted. The saline solution is then heated (not above 212°) and the steam 
is passed into the second cylinder. After about an hour a tap between the 
two cylinders is turned, and the one containing the compressed steam is placed 
in a vessel of Cold water. 
Diminution of Temperature in maldng Alloys.- — It was stated by Dr. 
Phipson, at a late meeting of the Paris Chemical Society, that a very sudden 
fall of temperature is occasioned by mixing certain metals together. The 
most extraordinary descent of temperature occurs when 207 parts of lead, 
118 of tin, 284 of bismuth, and 1,617 of mercury are alloyed together. The 
external temperature being at -j-170° Centigrade at the time of the mixture, 
the thermometer instantly falls to — 10° below zero. Even when these pro- 
portions are not taken with absolute rigour, the cold produced is such that 
the moisture of the atmosphere is immediately condensed on the sides of the 
vessel in which the metallic mixture is made. The presence of lead in the 
alloy does not appear to be so indispensable as that of bismuth. Dr. Phipson 
explains this fact by assuming that the cold is produced by the liquefaction 
at the ordinary temperature of thfe air of such dense metals as bismuth, &c., 
in their contact with the mercury. — Vide The Reader , May. 
The Cigar-Boat. — This vessel, which was supposed to effect such a revolu- 
tion in the physics of ship-building, does not appear to have the wonderful 
power which was theoretically attributed to it, if we may believe the French 
pilot who brought the Havre boat to London. He says her average speed 
was 7 to knots an hour. She behaved exceedingly well at sea, rolling 
less than other vessels, which must be due rather to a judicious disposition of 
the weights aboard than to any stability derivable from the round form of her 
immersed transverse section. 
Deviation of the Compass in Iron Ships. — Mr. Hopkins, who has for a 
long while been experimenting on this subject, looks upon an iron ship 
as a huge bar-magnet, whose polarity he proposes to neutralize by means 
of magnetic batteries of great power, and thus remove all deviation. Mr. 
Hopkins has received permission from Sir John Hay, the chairman of 
the Millwall Ship-building Company, to experiment upon the Northumber- 
land, during the space of four months. This vessel has been built and plated 
