Page:Popular Science Monthly Volume 21.djvu/150

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142
THE POPULAR SCIENCE MONTHLY.

mit that parasites in many cases do no perceptible harm. To these cases may be opposed the numerous instances in which they have proved destructive to their hosts, whether animals, birds, or men, often carrying off multitudes of creatures when they become excessively abundant on a species; and in the most favorable cases they give the host discomfort and inconvenience, though their work maybe overlooked in the presence of his superior vigor. As a rule, parasites belong to the lower orders of animals—worms or insects. Sometimes an arachnoid or a crustacean will join the company; but a few small fishes are the only creatures among the vertebrates that ever assume that relation. The stories that have been told of the existence of other inhabitants in the system are either fables or have originated in the accidental presence of single individuals who were probably as much astonished as their host at finding themselves in such a home.

 

The Repeating Melograph.—M. J. Carpentier exhibited, at the recent electrical exhibition in Paris, an instrument called the repeating melograph, by means of which, he claimed, any piece or improvisation which a composer may play on the key-board to which it is attached is registered, and may be repeated upon any other instrument with which it may be connected. It, more-over, secures the repetition, not of the piece only, but of the style, even to the false notes, of the player. Both processes, the registering and the repeating of the piece, are performed through the medium of electric currents. In the former case the keys of the instrument on which the piece is played are connected with wires through which a current is established when the key is pressed down. This current sets in operation an apparatus, with tools answering to the several keys, by means of which a perforation corresponding in character with the musical value of the note is made in a moving band of paper. The piece being finished, the band is ready to serve in a second execution of it. Electric communication is effected between the perforated band and the second instrument; and a current is formed, causing a corresponding key to be sounded at each perforation of the band as it passes the circuit in the process of unrolling. M. Carpentier contemplates adjusting his instrument so that it may also be made to print the piece in ordinary musical type.

 

Electric Units.—The International Congress of Electricians at Paris unanimously agreed upon a uniform standard of electrical units of measurements. It decided to adopt the fundamental units, the centimetre, the gramme, the second (C. G. S.); that the practical units, the ohm and the volt, should be defined, as now, the ohm as 109, and the volt as 108; that the unit of resistance (ohm) be represented by a column of mercury having a section of a square millimetre at the freezing-point, and a height to be determined experimentally by the International Committee; that the current produced by a volt in an ohm be called an ampere instead of a weber, the latter name having been applied by Weber himself in Germany to a current of ten times less force; that the name of coulomb be applied to the quantity of electricity defined by the condition that an ampère gives a coulomb a second, the former English weber; and that the name farad be applied to the capacity defined by the condition that a coulomb in a farad gives a volt—which is equivalent to the farad of the British Association. The Carcel lamp was recommended to be continued as the standard for the comparison of lights, pending the investigations of an International Committee to ascertain and fix upon the most practicable standard.

 

"Clouds of Seeds."—A correspondent of "La Nature" describes a remarkable appearance of seeds in the air that was observed in Guatemala during eight consecutive days in February last. In the early hours of the afternoon it was easy to perceive at a certain distance from the ground bodies resembling snow-flakes, which appeared and disappeared instantaneously, generally going in the same direction, but which were visible only when they passed between the sun and the observer. They moved gracefully, with variegated colors, falling and then rising out of sight, as snow-flakes do when they melt in the air; at other times they were carried along by the