As the Opera does not give representations every day, Mr. Ader has had the idea of occupying the attention of the public on Tuesday, Thursday, Saturday, and Sunday with the telephonic effects of flourishes of trumpets, which imitate pretty well the effects of French horns.  These experiments have taken place in the hall in which is installed the little theater, and we must really say that in the effects produced French horns count for nothing.—­La Lumiere Electrique.

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THE ACTION OF COLD ON THE VOLT

When the voltaic arc plays between two metallic rheophores, of copper for instance, each formed of a U-tube traversed by a rapid current of cold water, and placed horizontally opposite each other, the following facts are observed:  The luminous power of the arc is considerably weakened; it is reduced to a mere luminous point even when a current of 50 to 75 Bunsen elements of the large pattern is employed.  The arc is very unstable and the least breath is sufficient to extinguish it.  If a leaf of paper is placed above the arc at the distance of 0.004 to 0.005 meter a black point is produced in a few moments, which spreads and becomes a perforation, but the paper does not ignite.  The arc consists of a luminous globule, moving between the two rheophores up and down and back again.  The form of this globule, as well as its extreme mobility, causes it to resemble a drop of water in a spheroidal state.  If we approach to the voltaic arc the south pole of a magnet the arc is attracted to such a degree that it leaves the rheophores and is extinguished.  The same facts are observed in an intense form on presenting the north pole of a magnet to the arc.  The quantity of ozone seems greater than when the arc is not refrigerated.  It is to be noted that notwithstanding the refrigeration of the rheophores the flame of the arc is slightly green, proving that a portion of the copper is burning.  It becomes a question whether the arc would be produced on taking as rheophores two tubes of platinum in which is caused to circulate, e.g., alcohol cooled to -30 deg..—­D.  Tommasi.

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WATCHMAN’S DETECTER.

We herewith illustrate an exceedingly simple form of detecter, to show if the night watchmen perform their visits regularly and punctually.  In the case, C, is a clockwork apparatus driving the axle, S, at the end of which is a worm which gears into the wheel of the drum, D. The rotation of D, thus obtained unrolls a strip of paper from the other drum, D. This paper passes over the poles of as many electro-magnets as there are points to be visited, and underneath the armatures of these electro-magnets.  Each armature has a sharp point fixed on its under side, and when a current passing through the coils causes the attraction