Read Ebook: The Salving of the Fusi Yama: A Post-War Story of the Sea by Westerman Percy F Percy Francis Hodgson E S Edward Smith Illustrator

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THE ELECTRIC CURRENT, AND ITS PRODUCTION BY CHEMICAL MEANS. PAGE

Production of electric current in chemical battery--Current very weak--Current compared to circulation of the blood--Strength and volume of current--Pressure not sufficient without volume--Action of current is instantaneous--Resistance to the passage of the current--Copper the usual metal for conductors--Heat produced by current when wire is too small 1

PRODUCTION OF ELECTRIC CURRENTS BY MECHANICAL MEANS.

Current produced by mechanical means--Alternating current-- Magneto-electric machines--Shock produced by interruption of current--The current must be commutated--Description of commutator--Current, though alternating in the dynamo, is continuous in the circuit--Continuous current used for electro-plating 5

Current will magnetise an iron or steel bar--Permanent magnet-- Electro-magnet--Where the magneto and dynamo machines differ-- Armature of so-called continuous-current dynamo--Type of commutator--Commutator brushes--Current continuous in the circuit--Alternating-current dynamos--Current not commutated-- Intense magnetic field produced--Simplicity of Ferranti armature-- Large number of alternations of the current--Alternating current cannot be used to excite an electro-magnet--Exciter coupled on to same spindle as dynamo--Power of exciter if used alone 9

ELECTRIC LAMPS.

Production of electric light--Arc lights--Mechanism to regulate carbons--Some lamps suitable for alternating current--When carbons are consumed, light goes out--Arc lamps very complicated-- Jablochkoff candles--Arc formed between the carbons--Candles require alternating current--Incandescent lamps--Vacuum formed in lamps prevents combustion--Vacuum not perfect--Advantages of incandescent lamps for house and ship lighting--Unaffected by wind, and suitable for either continuous or alternating currents 19

LEADS.

Leads made usually of copper wire--Short circuit--High E.M.F. for arc lights, but low for incandescent--Arc lights in series-- Incandescent lamps in parallel circuit--E.M.F. same for one lamp as for a number--If lamps suitable, each one turns on and off separately--Safety fuses 24

SHIP LIGHTING.

Position for dynamo--Dynamo to be kept clean and cool--Quick-speed engines--Slow-speed engines with belts--Means of keeping belt on the pulley--Engine must work steadily--A good sensitive governor wanted--The belt must be kept tight--A handy belt-stretcher-- Friction gearing--Switch board near dynamo--Leads of different colours--Main leads and branch leads--Lamps held in frosted globes--Switches for each lamp--Lamps of various candle-powers-- Plan for lighting quarter-deck at times--Arrangement of temporary leads--Leads and lamps always ready, and easily fixed up--Lighting of ships' holds--Danger of fire with oil lamps--Arc lamps not suitable--Arrangement of leads for incandescent lamps-- Work carried on better, and pilfering of cargo prevented--Hold leads disconnected while at sea--Installation complete--Lights wanted as night approaches--Precautions before starting dynamo-- Lubrication must be perfect--Commutators and collectors require very little oil--Position of brushes--Start the engine--Switches not turned on; no current except from exciter--Testing work of exciter--Dynamos very powerful magnets--Look out for your watches--Switch on the lamps--Current is produced in large dynamo-- Difference of a few lamps compensated by governor--Turn all lamps on, and light up gradually--Inequality of light in different lamps--Weeding out of bad lamps--Lamps not to be run too bright-- No trouble with dynamo if oiling is attended to--Seizing--Oil must be thin--The dynamo must be kept clean--Little troubles with the lamps--No safety fuse--Effects of vibration of ship on lamps-- What to look to if a lamp is out.--Recapitulation--A current of 50 volts is hardly felt--Incandescent lights for side lights-- Mast-head light--Arc light should never be used--Present mast-head light quite powerful enough--On passenger steamers, side one blaze of light, and side lights barely visible--Speed of dynamo constant, but steam power used in proportion to number of lamps in use--No danger to life from electric current on board ship-- Binnacle lamps. Electric light not suitable--Dynamo if near a compass will affect it--Notes 27

WRINKLES IN ELECTRIC LIGHTING.

THE ELECTRIC CURRENT, AND ITS PRODUCTION BY CHEMICAL MEANS.

It will first be necessary to explain how electric currents are produced by means of chemicals. In a jar A, Fig. 1, are placed two plates B and C, one zinc, and the other copper, each having connected to it at the top a copper wire of any convenient length. The plates are kept in position by means of pieces of wood, and the jar is about half filled with a solution of salt and water, or sulphuric acid and water; if then the two wires are joined, a current of electricity at once flows through them, however long they may be. The current produced in this manner is very weak, and does not even keep what strength it has for any length of time, but rapidly gets weaker until quite imperceptible. The current is, however, continuous; that is, it flows steadily in the one direction through the wire, and may be used for ringing bells, or for other purposes where a feeble current only is required to do intermittent work. The wire E in connection with the copper plate is called the positive lead, and the other the negative, and the current is said to flow from the copper plate, through the wire E through the circuit to D, and thence to the zinc plate, and through the liquid to the copper plate. The current has often been compared to water flowing through a pipe, but I think it can be better compared to the blood in the human body, which through the action of the heart is continually forced through the arteries and veins in one steady stream. There is, however, this difference, that there is no actual progression of matter in the electric current, it being like a ripple on water, which moves from end to end of a lake without the water itself being moved across. Now that I have given you an idea of how the current acts, I must try and explain how different degrees of strength and volume are obtained. In the first place, let us consider what constitute strength and volume in an electric current, or at least try and get a general notion about them. For this purpose I shall compare the electric current to water being forced through a pipe; and the strength of the electric current, or electromotive force, written for short E.M.F., will be like the pressure of water at any part of the pipe. Two pipes may carry different quantities of water, and yet the pressure may be the same in each; in one a gallon of water may pass a given point in the same time that a pint passes the same point in the other, and yet in each case the different quantities may pass that point at the same speed. Thus in electricity, two currents may be of different volume or quantity, measured in amp?res, and yet be of the same E.M.F. measured in volts; or they may be of different E.M.F., or pressure, or intensity, and yet be of the same volume. If any work is to be done by the water forced through a pipe, such as turning a turbine, it is evident that pressure of itself is not sufficient, seeing that a stream an inch in diameter may be at the same pressure as another a foot in diameter. So with the electric current, if work is to be done, such as driving a motor or lighting a lamp, it is not sufficient to have a certain E.M.F.; there must be quantity or volume in proportion to the amount of work, so that if it takes a given quantity to work one lamp, it will take twice that quantity to work two lamps of the same kind. It must not be inferred from this, that if one lamp requires a certain E.M.F., that two lamps will require it to be doubled, as such is not the case, except under certain conditions which I will explain later on.

The action of electricity is practically instantaneous in any length of wire, so that if the current is used to ring two bells a mile apart, but connected by wires, they will commence to ring simultaneously. I have so far not said anything about resistance to the passage of the current through the wires. I shall therefore refer again to our comparison of the current to water forced through a pipe, and you will agree that a certain sized pipe will only convey a certain amount of water in a given time. If a larger quantity is to be conveyed in the same time, a greater pressure must be applied, or a larger pipe must be used.

It is evident that increasing the size of the pipe will get over the difficulty more readily than increasing the pressure of the water. The pipes themselves offer a certain resistance to the passage of the water through them, in the shape of friction; so that if an effect is to be produced at a distance, rather more pressure is required than if it is done close at hand, so as to make up for the loss sustained by friction.

Much the same may be said of the electric current; a certain sized wire will only carry a certain current, and if more current is required, a thicker wire must be used to convey it, or it must be of a greater E.M.F. It is usually more convenient to increase the thickness of the wire than to increase the E.M.F. of the current. The wire offers a certain resistance to the passage of the current through it, which may be compared to friction, and this resistance varies according to the metal of which it is composed. Copper is the metal in ordinary use for wires for electric lighting purposes, and the purer it is the better will it convey the current. Iron is used for telegraph wires on account of cheapness, the current used being so small that this metal conveys it readily enough; if copper were used, the wires will only require to be about one-third the diameter of the iron ones. The following are the respective values for electrical conductivity of various metals when pure, taking silver as a standard:--Silver 100, copper 99?9, gold 80, zinc 29, brass 22, iron 16?8, tin 13?1, lead 8?3, mercury 1?6.

"Claptrap!" declared Villiers, taking up the menu-card, which represented something rather more concrete, and consequently rather more digestible, than the newspaper announcement.

"P'raps," admitted Claverhouse, with his characteristic drawl. "'Tany rate the bloke's straightforward enough to tell you that you might be chucking your money away."

"That's so," agreed Beverley. "We can investigate. I suppose there's no obligation to carry on if the thing looks fishy."

"I don't mind going that far," said Villiers. "And if it looks a sound scheme I'll plank down three hundred. After all three hundred is only worth about a hundred and eighty pounds, and if we are kept employed for a twelvemonth and get a bit of excitement chucked in, well--we might just as soon spend our gratuities that way as being rooked and rushed at home."

Beverley made no audible comment. He was of a cautious nature, and his cautiousness was heightened by the fact that he was responsible for the maintenance of a young brother for at least a couple of years.

While the waiter was taking orders the subject was dropped, but as soon as the man had departed Claverhouse returned to the matter.

"Wonder if it's a filibustering stunt?" he hazarded.

"Or piracy," added Villiers. "I heard a yarn floating around only yesterday about a merchant skipper whose crew were killed in cold blood by a U-boat. The old man was taken prisoner, but managed to escape, and now he's vowed to get his own back. How I don't know, unless he turns pirate and goes for every Fritz he falls in with on the high seas."

"Thanks, I'm not having any there," declared Beverley. "I don't want to find myself hanging in the modern equivalent to Execution Dock."

"And Air Force blokes," said Claverhouse gently.

"Nothing like sticking up for your own crush, old bird," remarked Villiers. "Yes, that part puzzles me a bit. Look here, let's take Beverley's advice and make inquiries. If it isn't all jonnick we can pipe down."

"When?" asked Claverhouse. "Now? At once?"

Villiers laughed.

"Hardly," he replied. "Pretty guys we'd look trotting round to Richborough Chambers and asking for 'Joystick'. It's too much like asking for trouble to my mind. No, the best thing we can do without compromising ourselves is to write and ask for an interview. Then we can resolve ourselves into a Committee of Ways and Means."

"Joint letter?" asked Beverley.

"No, individual, briefly stating our qualifications," replied Villiers.

"But, in that case, you or I might be sent for and the others ignored," objected Claverhouse. "I vote we stick together--united we stand sort of touch."

"That's the stuff to give 'em," was Villiers' rejoinder.

To the Rescue

It was not until the following Thursday afternoon that Villiers, as head of the informal Mutual Advancement Syndicate, received a reply to the joint letter to "Joystick".

As Villiers had expected, the letter gave no clue to the nature of the proposed undertaking, but consisted of a brief intimation that the advertiser would be pleased to interview Messrs. Villiers, Beverley, and Claverhouse at Richborough Chambers at 3 p.m. that day.

"We're progressing," he observed, as he handed the letter to Bobby. "Now comes the fun. Will 'Joystick' take a rise out of us, or shall we pull his leg? Let's go round and rout out Claverhouse."

"He'll be at his one-horse show garage," said Beverley. "Better look him up at lunch-time."

"Won't give him enough warning," objected Villiers. "We'll tackle him at once and let him know how things stand. 'Raise steam and prepare for immediate action', eh, what?"

They happened across Alec Claverhouse just outside the motor-works. He was about to take a 60-h.p. "Odouresque" out for a test run.

"Cheerio!" he exclaimed. "Any luck?"

"Read this," replied Villiers. "My festive friend, you'll have to pipe down this afternoon. Thursday's 'Make and mend', you know."

"Not in this rotten show," said Claverhouse. "The civilian equivalent to the Adjutant bird in these works is a regular Cossack for granting time off. I haven't a great grandmother to bury, nor is there a football match on this afternoon, so honours are even on that score. What do you think of this little lad? Guess I'll knock sixty out of her on the road."

"In that case," remarked Beverley, "you'll get run in by the police and sacked by the firm, so before you do find yourself in the cart why don't you apply for leave?"

"I will, sure," replied Claverhouse, throwing off his leather-lined coat and tossing it into the coup?. "Hang on half a tick, and I'll tell you the result of the poll."

He disappeared from view, leaving Jack and Bobby to admire the workmanship and general "get up" of the powerful "Odouresque".

In less than five minutes he reappeared, beaming and smiling.

"It's all O.K.," he announced. "I cut the rotten red tape and saw the manager. While I was about it--'in for a penny, in for a pound' stunt you know--I asked if he had any objection to you fellows coming with me. Said he hadn't, as long as the firm hadn't to pay your funeral exes; so hop in and let's get a move on."

Nothing loth the two chums boarded the car, Villiers sitting by Claverhouse while Beverley reclined in lordly fashion on the back seat. Almost imperceptibly, in response to a touch of the electric starter, the powerful car glided away.

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