tube is filled with a peculiar glow or light, abounding in Stokes' rays.

The experiments with the vacuum tube, and especially Gassiot's cascade, are, as might be expected, very beautiful. When a coal-gas vacuum tube of considerable diameter, and conveying the full discharge from the secondary coil, is supported over a powerful electro-magnet axially, the discharge is condensed and heat is produced.

"If placed equatorially, the heat increases greatly, and when the discharge is condensed and impinges upon the sides of the glass tube, it becomes too hot to touch, and if the experiment was continued too long the tube would crack.

"The enormous quantity of electricity of high tension which the coil evolves, when connected with a battery of 40 cells, is shown by the rapidity with which it will charge a Leyden battery.

"Under favorable circumstances, 3 contacts with the mercurial break will charge 40 square feet of glass.

"On one occasion a series of 12 large Leyden jars arranged in cascade were discharged; the noise was great; and each time the spark (which was very condensed and brilliant) struck the metallic disc, the latter emitted a ringing sound, as if it had received a sharp blow from a small hammer.

"The discharges were made from a point to a metallic disc; and when the former was positive the dense spark measured from 18 to 18 inches, and fell to two and one-half inches when the metallic plate was positive and the point negative.

"Variations of the Leyden-jar experiments were tried by connecting the coil worked by a quantity battery of 25+ 25 cells with 6 Leyden jars arranged in cascade, and the spark obtained measured 8 inches.

"The same 6 jars connected with the coil, when the 50 cells were arranged continuously for intensity, gave a spark of 12 inches, of very great density and brilliancy."

ELECTRICITY APPLIED TO

REGISTERING VIBRATIONS.

The laws which govern the vibration of cords or wires have been obtained by comparing the sounds they produce with the notes of a syren. Without questioning the accuracy of this method, it will still be desirable to obtain the laws of vibration without regard to the effects which vibrations produce; a direct registry cannot fail to be more satisfactory. Now it is clear that however rapid may be the vibrations of a cord, the velocity of the electric force is greater; moreover, it is not impossible to make a succession of electric impulses produce a corresponding succession of permanent effects, which can be seen and counted, so that if a vibrating body can be made to open and close an electric current, the electric force may be depended on to register its vibrations. The practical questions are, first, How shall a vibrating body be made to open and close an electric current without hav

ing its motion embarrassed? Second, How, in a legible manner, can the number of these rapid impulses be registered? And, third, By what means can the time of vibration be accurately measured? To register the vibration of cords and piano-wires, the following arrangement of apparatus has been made. Through the middle points of the vibrating cord passes a firm cambric needle, the point of which will, when the cord is at rest, be very near, but not in contact with the surface of mercury contained in a cup beneath. A galvanic battery is connected, one pole with this cup, the other with a trough, containing mercury, into which dips the end of a wire bent twice at right angles, and turning freely upon a hinge. To this wire is joined one end of the helix of an electro-magnet, while to the other end of the coil is attached a flexible metallic thread (a ravelling of gilt lace) tied into the eye of the needle, which passes through the vibrating cord. Now, by the vibration of the cord, the needle-point will be brought in contact with the surface of the mercury under it at the end of every double vibration, and a current of electricity darts through the wires, magnetizes the electro-magnet, which pulls the armature to its poles, and brings the registering point in contact with the paper. As the paper is drawn swiftly along by clock-work, while the armature with its sharp and soft lead-pencil point is in motion, the vibrations of the cord are registered upon the paper in a line of distinct black dots, easily counted. To measure time, in the present form of the apparatus, a pendulum is used. The pendulum when drawn to one end of its arc rests against one arm of a lever, while the other arm carries a pair of pluckers which grasps the cord. A pressure of the finger causes this finger to release, at the same instant, the pendulum from one end, and the cord from the other. The wire, whose lower end dips into the trough of mercury, can at any time be brought into the arc of the pendulum, by moving the block to which it is fastened, without breaking the circuit; but when this is done, the ball will strike its upper end, and, knocking it over, lift the lower end from the mercury, and open the circuit. The motion of the armature begins with the beginning of the first vibration of the pendulum, and stops at the end of 1, 3, or any odd number of seconds, and the number of dots left upon the paper shows the number of vibrations of the cord. The vibrations of the wire are made to occur in a vertical plane opening and closing an electric circuit with corresponding rapidity, and a dot is made upon the moving paper at the moment when the lowest point in the vibration is reached. The experiment begins when the wire is above its line of rest; the first dot, therefore, represents one-half of one complete vibration. Should the experiment end when the wire is at the highest point in its motion, the number of dots would show the exact number of complete vibrations made; but since it may end when the wire is at any point of its path, there may be a possible error of less than one-half of a complete vibration in an experiment one second in length. As the time is lengthened, the error is diminished; in a registry of 5 seconds the maximum error would be less than one-tenth of one vibration per second.

The precision with which the laws of vibration may be verified by the use of this instrument is in the highest degree satisfactory. However numerous the repetitions of an experiment may be, the registry varies only by a single dot. Moreover, it makes the law rest upon no comparison of sounds produced by the vibrations, nor upon any other effect of the motion, but upon the vibrations themselves, whose numerical relations are directly shown. Vibrations, sonorous or otherwise, are thus equally the subject of experimental investigation.

Prof. Cooley gives this table of vibrations, which differs from all others relating to music; first, in being the result of a direct registry; and, second, in that it shows all the intervals of the scale. The piano upon which the registry is based was tuned to the standard pitch of the Boston Music Hall organ.

The octave above A= 208.5 is the la usually referred to in describing the pitch of the orchestra; it is thus produced by 417 complete vibrations per second.

It

In the time of Louis XIV., the pitch of this A was, according to Sauveur, 405 vibrations per second, while by the action of the congress called together by the Society of Arts, at London, in 1860, it was 440. The same note sounded by Handel's tuning-fork (1740) is said to have been made by 416 vibrations per second. will be thus seen that while the present pitch is nearly one-half of a tone higher than that referred to by Sauveur, and considerably more than that interval lower than that of the London Congress, it agrees with the pitch adopted by Handel, to within a single vibration.-Prof. Cooley, Journal Franklin Institute.

CONDUCTING POWERS OF MATERIALS.

According to the experiments of Mr. M. G. Farmer, made some years since, the relative electrical resistance of different metals

and fluids at ordinary temperatures is as follows, pure copper

being taken as 100:

The following table gives the specific resistance in ohms (an ohm is an amount of resistance equal to that exerted by one-sixteenth of a mile of common galvanized iron telegraph wire No. 9) of various metals and alloys, at 32° Fah., according to the most recent determination of Dr. Matthiessen:

The use of this table is as follows: Suppose it is required to find the resistance at 32° Fah. of a conductor of pure hard copper,

weighing 400 lbs. per knot. This is equivalent to 460 grains per foot. The resistance of a wire weighing one grain is found by the table to be 0.2106; therefore the resistance of a foot of wire weighing 460 grains will be 22106; but the resistance of one knot will be 6,087 times that of one foot; therefore the resistance required will be 6.0870-21062.79 ohms. If the diameter of the wire be given, instead of its weight per knot, the constant is taken from the second column. Thus the resistance at 32° Fah. of a knot of pure hard-drawn copper wire 0.1 inch in diameter would be 6087994-6.05. The resistance of wires is materially altered by annealing them, and a rise in temperature increases the resistance of all metals. Dr. Matthiessen found that for all pure metals the increase of resistance between 32° and 212° Fah. is sensibly the same. The resistance of alloys is much greater than the mean of the metals composing them. They are very useful in the construction of resistance coils.

10000

The highest value which has probably been found for the conducting power of pure copper is 60 times that of pure mercury, according to Sabine. Commercial copper may be considered of good quality when its conducting power is over 50. Different samples of copper vary greatly in their specific conductivity, as may be seen by the following table, which gives the result of careful determinations by Dr. Matthiessen, the conducting power of pure copper at 59.9° Fah. being taken as 100.

Thus Rio Tinto copper possesses no better conducting power than iron. This shows the great importance of testing the conductivity of the wire used in the manufacture of electro-magnets, cables, etc.

VEGETABLE ELECTROMOTORS.

The "Chemical News" contains an article contributed by Edwin Smith, M.A., giving results of researches in a field which, so far as we are aware, has been hitherto untraversed. He says: "It is well known that a voltaic combination may be made of two liquids and a metal, if one of the three acts chemically upon one and only one of the other two; thus, we may employ copper, nitrate of copper, and dilute nitric acid, or platinum, potash, and nitric acid. Connect a platinum crucible with one terminal of a galvanometer, pour in a little solution of caustic potash, place in this the bowl of a tobacco-pipe having the hole stopped up with wax, pour into the bowl a little nitric acid, dip in the acid a small slip of platinum foil, and connect this with the other ter