Scientific American Supplement, No. 611, September 17, 1887 | Page 8

on the track, the engine may be doing 25 horse power to get that amount there through the gears and cable. With heavier loads this is somewhat diminished, but about the very best figure that can be put forth is but 35 per cent. recovery, with 65 per cent. loss--the exact converse of electricity under heavy loads.--_Street Railway Journal._
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ELECTRICAL ALARM FOR PHARMACIES.
[Illustration: FIG. 1.]
To avoid the errors which sometimes occur in a pharmacy or in a laboratory, where one bottle is taken for another, especially in the case of those containing highly poisonous or dangerous substances, a simple arrangement, shown in the cuts, has been proposed. The apparatus, in principle, is a species of electrical alarm, in circuit with an ordinary house telegraph line. It consists essentially, as shown in Fig. 1, of a battery, bell, and pedestal, provided with an electric contact on which the flask rests. Fig. 2 shows this contact or break piece. On a series of pedestals thus arranged and intercalated in the same circuit the flasks containing poisonous or dangerous substances, whose inadvertent handling might cause trouble, are placed. In removing one of these flasks the circuit is closed, and the electric bell notifies the pharmacist of the danger attendant on the use of the substances contained in the flask referred to, thus guarding against the errors due to carelessness, and quite too frequent, especially in pharmacies.--_Chronica Cientifica._
[Illustration: FIG. 2.]
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APPARATUS FOR DETERMINING MECHANICALLY THE REACTION PERIOD OF HEARING.
The following apparatus, constructed after the designs of Dr. Loeb, assistant in the Physiological Institute at Wurzburg, is for the purpose of measuring the reaction period of hearing, that is, the period which elapses between the time when a sound wave affects the auditory nerve and is thence transferred to the brain, then affecting the consciousness, and the moment when the motor nerves can be thrown into action by the will. It is, therefore, necessary to fix both instants--when the sound is produced and when the observer has, from its warning, received the impulse so as to press down a key. The great advantage of this instrument over others adapted for the same end consists in this, that the determination in its essentials is effected entirely by mechanism, and, therefore, the graphic results attained by it are free from all sources of error, which errors other methods always introduce to a greater or less extent. Thus its results are quite unexceptionable.
[Illustration: REACTION PERIOD OF HEARING.]
The apparatus shown in the cut rests on three feet, two of them consisting of strong screws, so that by aid of the circular level, l, on the base plate, it can be adjusted perfectly level. On a little shelf attached to a square rod, seen on the left of the instrument, rising from the base plate, and near its top, is a horizontal tube, through which, by a bulb not shown in the cut, a blast of air can be blown. In front of the other opening of the tube is a horizontal fork of ebonite, whose arms carry on the side opposite the tube a metallic ball. Through the arms of the fork pass the wires of the circuit of an electric battery. These terminate in two rounded ends, which, when the arms approach each other, are touched by the metallic ball, so that the latter also closes the metallic circuit. By the blast of air a wooden wedge contained in the tube is driven between the arms of the fork, the ball falls from them, and the electric stream is cut off. The ball drops upon the inclined metallic plate, p, bounces off it, and is received in a little sack, S. When the observer hears the ball strike the plate, he presses on the key, t, and the interval between the two instants, namely, the falling of the ball upon the plate and the pressing of the key, t, is what is to be mechanically fixed and measured.
The electric current, which is closed by the ball as long as it lies on the jaws of the fork, flows around the arms of the electro-magnet, m, which continually attracts an armature fastened to a lever arm, and coming over the poles of the magnet. If the circuit is broken by the fall of the ball, the armature at once rises upward. By this a spring contained in the tube, g, and hitherto kept compressed, is released, which gives a shock to the right angled frame, a a, containing a blackened or smoked plate of glass, so that, following the wire, b, acting as a guide, the plate flies from left to right of the apparatus. To prevent the plate from recoiling, a catch, d, is fastened to the side bar, c. Furthermore, lest