Part 20 (1/2)
[Illustration: FIG 151_b_]
[Illustration: FIG 151_c_--Section of a gra 151_c_ the construction of the gramophone reproducer is shown in section A is the cover which screws on to the bottoated into a tubular shape for connection with the horn, an arainst the rubber ring C to ht joint The needle-carrier N is attached at its upper end to the centre of the diaphragh it and the cover The lower end is tubular to accommodate the steel points, which have to be replaced after passing once over a record A screw, S, working in a socket projecting from the carrier, holds the point fast The record moves horizontally under the point in a plane perpendicular to the page The groove being zigzag, the needle vibrates right and left, and rotating the carrier a lass diaphragra instrument only The records arethe recorder point to describe a spiral course froramophone records have ason a ten-inch ”concert” record is about 1,000 feet
THE MAKING OF RECORDS
For commercial purposes it would not pay toers and instrumentalists renders such a method impracticable All the records we buy are made from moulds, the preparation of which ill now briefly describe
CYLINDER, OR PHONOGRAPH RECORDS
First of all, a wax record istested and approved, it is hung vertically and centrally fro up through the record On one side of the table is a piece of iron On each side of the record, and a slass tube The top of the rods are hooked, so that pieces of gold leaf lass is now placed over the record, table, and rods, and the air is sucked out by a puood vacuum has been obtained, the current from the secondary circuit of an induction coil is sent into the rods supporting the gold leaves, which are volatilized by the current junet, whirled outside the bell-glass, draws round the iron armature on the pivoted table, and consequently revolves the record, on the surface of which a very thin coating of gold is deposited The record is next placed in an electroplating bath until a copper shell one-sixteenth of an inch thick has formed all over the outside This is trued up on a lathe and encased in a brass tube The ” it till it contracts sufficiently to fall out of the copper mould, on the inside surface of which are reproduced, in relief, the indentations of the wax ” it in a tank of melted wax
The cold metal chills the wax that touches it, so that theThe mould and copy are removed from the tank and mounted on a lathe, which shapes and smooths the inside of the record The record is loosened fro After inspection for flaws, it is, if found satisfactory, packed in cotton-wool and added to the saleable stock
Gramophone master records are made on a circular disc of zinc, coated over with a very thin film of acid-proof fat When the disc is revolved in the recording h the fat and exposes the zinc beneath On immersion in a bath of chromic acid the bared surfaces are bitten into, while the unexposed parts re is considered coative copper copy isThis constitutes the mould From it as many as 1,000 copies
[32] The Edison Bell phonograph is here referred to
[33] So sounds of the voice are computed to be represented by depressions less than a millionth of an inch in depth
Yet these are reproduced very clearly!
Chapter XVII
WHY THE WIND BLOWS
Why the wind blows--Land and sea breezes--Light air and moisture--The barometer--The column barometer--The wheel barometer--A very simple barometer--The aneroid baro-dress--Air-pu door-stop--The action of wind on oblique surfaces--The balloon--The flying-h a slight leakage of air, and loses some of its bounce, it is a common practice to hold it for a few minutes in front of the fire till it becoain
Why does the heat have this effect on the ball? Nothe chapter on the steaine the reader will be able to supply the answer ”Because theone another when the air is heated, and by striking the inside of the ball with greater force put it in a state of greater tension”
If we heat an open jar there is no pressure developed, since the air simply expands and flows out of the neck But the air that re less in quantity than when it was not yet heated, weighs less, though occupying the same space as before If we took a very thin bladder and filled it with hot air it would therefore float in colder air, proving that heated air, as we should expect, _tends to rise_ The fire-balloon e kept artificially war in so
Now, the sun shi+nes with different degrees of heating power at different parts of the world Where its effect is greatest the air there is hottest We will suppose, for the sake of argument, that, at a certain lobe is of equal temperature
Suddenly the sun shi+nes out and heats the air at a point, A, till it isair The heated air expands, rises, and spreads out above the cold air But, as a given depth of warht than an equal depth of cold air, the cold air at once begins to rush towards B and squeeze the rest of the warm air out
We may therefore picture the at along the surface of the earth to replace war over the upper surface of the cold air A similar circulation takes place in a vessel of heated water (see p 17)
LAND AND SEA BREEZES