SCIENTIFIC SUMMARY. 
419 
this crack, provided that the temperature of the ice and of the air he below 
0° centigrade. Obviously the knife acts in this instance like a diamond, 
which depresses minute particles of glass, and through the wedge-action of 
which a progressive linear cracking is produced, which renders fracture 
possible. A mere scratch suffices for neither glass nor ice. It is worthy 
of notice that these clear sharp cracks are possible in ice which is in con- 
tact with water in a warm room — a proof that ice preserves its brittle 
character at temperatures lying close to its melting point. The breaking 
off at the crack is on the other hand no longer possible, on account of the 
regelation in the upper part of the crack. — Ibid. 
Spectral Characters of Indium. — Messrs. Reich and Richter, the dis- 
coverers of this new metal, state that its presence is indicated in the spec- 
troscope by two blue lines, one of which, the brighter, corresponds to 
division 98 of the scale, and the other to 135. In some cases this mode of 
analysis becomes unnecessary, as the instant the indium salt is placed in 
the flame of the Bunsen lamp, it communicates to it a bright violet tinge 
which they consider to be sufficiently characteristic. 
The Beal Nature of the “ Electric Fly?'— The piece of apparatus which 
bears the latter name has had its history well worked out by Mr. Charles 
Tomlinson, who has compiled for the benefit of natural philosophers, an 
account of the various theories held regarding the character of this instru- 
ment. Mr. Tomlinson has been led from his numerous experiments to 
conclude that the theory requires a different expression for an aerial as 
compared with a liquid di-electric. It seems to have a different action in 
airs of different densities, and also according as it is wholly or partially 
enclosed. Its action, when the points are covered, is also distinct, and is 
equally peculiar in the presence of flame. Hence it may be said that 
“ there is no one expression that fairly represents the electric fly. It 
modifies its behaviour according to circumstances ; and, like a good sub- 
ject, has no law of its own, but conforms to the laws of the community of 
which it is a member.” — See Philosophical Magazine , No. 181. 
How to test for Ozone. — Mr. Lowe read a paper some time since before 
the Royal Society on the above subject. He thinks that the ordinary 
paper slips are apt to be fallacious, and that they do not indicate the 
intensity of the action of the ozone. He recommends the employment of 
the powder tests in preference to the paper slips. By inquiring into the 
action of various reagents on these powder masses, he has been enabled 
to draw the conclusion that a new method of investigating ozone is 
necessary. 
Gore's New Furnace. — In our Number for July, 1803, we gave a short 
notice of a new Patent Gas Furnace by Mr. G. Gore, of Birmingham. 
The principle of this furnace has since been applied upon a much larger 
magnitude, and furnaces, on a commercial scale, are now in use at the 
electro-plate manufactory of Messrs. Elkington, Birmingham, and else- 
wliere. These larger furnaces, as at present constructed, are capable of 
melting about 400 ounces of silver, copper, gold, or, if desirable, even cast- 
iron. The amount of coal-gas consumed in one of these furnaces varies 
from 300 to 400 cubic feet per hour. With a consumption of 360 cubic feet 
per hour, the following results have been obtained : — 266 ounces of sterling 
