398 
POPULAR SCIENCE REVIEW. 
from simple merciiiy ; but this same mercury, after having been submitted 
to the action of a current of hydrogen proceeding from the decomposition of 
water by the pile at a low temperature, and containing consequently traces 
of Ozann’s allotropic hydrogen, presented, though to a very slight degree, 
properties analogous to those of mercury which has served to disengage 
hydrogen electrolytically. From a number of fact^ like the foregoing, which 
experiments have shown him, the writer concludes (with Dumas) that hy- 
drogen is a gaseous metal. — Vide report of M. Crova’s memoir in Chemical 
Neivs, February 17th. 
Thermometer Alarum. — A curious instrument of this kind has been devised 
by M. Morin. The object of the apparatus is to give an alarm when the 
temperature falls below or rises above a desired degree. For example, in 
greenhouses, conservatories, &c., it is necessary to maintain a fixed tempera- 
ture, but it is not always convenient to keep a man watching the thermometer. 
By means of M. Morin’s instrument, the change of temperature is indicated 
by the ringing of a bell, which at once calls the attention to the alteration of 
heat. The apparatus consists of an ordinary thermometer, into the bulb of 
which a platinum wire is carried, another being brought through the top 
down to the point marking the degree of heat required. These wires are 
placed in connection with a small battery and electric alarum. So long as 
the required temperature is maintained, the circuit is complete ; but the 
moment the heat is diminished, the mercury falls, the circuit is broken, and 
a small electro-magnet lets fall an armature, which completes a circuit with 
the alarum. This now begins to ring, and continues to do so till the tern- 
O Oz 
perature rises again ^ to the proper height. The principle involved in the 
machine is similar to that on which our automatic railway signals are con- 
structed, and we only wonder it has not been put in operation before. — ^Vide 
Comptes Bendus, January 2nd, 1865. 
Electricity and Music. — It is stated by a contemporary that Mr. Barker, 
an organ-builder of Paris, is the inventor of a mode of applying electricity 
in the construction of great organs, so that the largest organ may be played 
as easily as a pianoforte, and the pipes may be distributed anywhere through 
a church. The invention is now being applied to a large organ in course of 
construction for the church of St. Augustin, in Paris. — Vide The Artizom, 
J anuary. 
Colour-Tops. — In our last number we described a form of the philosophic 
toy known as the colour-top, which had been devised by Mr. Swift, of Liver- 
pool. It appears that the subject of the trocheidoscope has been lately dis- 
cussed at a meeting of the Liverpool Architectural Society ; and in reference 
to some remarks made on that occasion, Mr. G. A. Audsley thus explains 
the contrivance arranged by him : — The general principles on which my 
instrument is constructed are the same as those on which the instruments 
invented some years ago by Mr. Pose are arranged. All I can claim for my 
machine is that, by adopting a verticad position for my revolving disks instead 
of the usual horizontal one, and by a very brilliant mode of illumination, I 
render the effects of colour visible at a great distance, and to any number 
of persons at a time. I have also introduced a series of compound motions, 
by which I obtain some striking effects, as well as continuity. Although I 
may have done a little towards the development of a very interesting and 
