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As a Discharge Gap

The fourth application of the mercury vapor apparatus, which has been frequently described in the technical press, is the Discharge Gap, sometimes called the interrupter. The function of the discharge gap is easily explained. For the production of X-rays, the sending of wireless telegraph messages, and many other purposes, it is necessary to have extremely sudden discharges of high-po

FIG. 8. CONVERTER WITH FOUR MERCURY POSITIVE ELECTRODES.

tential electricity. These are always obtained by introducing into the circuit from which the discharge is to be obtained, an air-gap or its equivalent, and by raising the voltage until this air-gap is unable to resist the strain, and breaks down. At this instant, there is a very sudden rush through the circuit of the electricity which has been previously accumulated on both sides of the air-gap; and this sudden discharge serves to send the wireless message, or excite the X-ray tube. But a disadvantage to be found with air-gaps is, that, even after they break down, they introduce a considerable resistance into the circuit, which pre

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vents this discharge from being perfectly free as is most desirable. A further disadvantage to be met with in the air-gap is that an undesirably long time is required for it, when once it has been heated by the discharge, to cool sufficiently to be able to operate properly a second time. In addition, whenever these gaps are used for large quantities of energy, or continuously, the metal electrodes become scarred and burnt, and require constant replacing.

The mercury vapor apparatus shown in Fig. 7 may serve the same purpose as the air-gap, for, if we apply a comparatively low voltage between the two electrodes, no current will flow, because of negative electrode resistance, unless we raise the voltage sufficiently to overcome this resistance. Then the discharge of electricity will be practically free, since, when once broken down, the negative electrode resistance is substantially eliminated. Thus, by the use of the mercury vapor apparatus, the resistance to the discharge, introduced by an air gap, is eliminated.

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Furthermore, it is found by trial, that, even with a series of the most rapid discharges, the negative electrode resistance can always be re-established between them, which is by no means true of the air-gap. And again, evidently, the burning and burring of the electrodes of the air-gap are eliminated, as the mercury cannot corrode in a vacuum.

The action of the mercury vapor discharge gap has been carefully studied by the rotating mirror method, and has been found to be free in a remarkable degree from the weaknesses of the air-spark gap. Fig. 7 shows a discharge gap used by Mr. Hewitt in his laboratory on some of his high-tension work. These bulbs are about five inches in diameter.

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Training of the British Tar

Foundation of Britannia's Maritime Supremacy-The Drilling of Seamen,
Upon Whose Efficiency Chiefly Depends the Strength of
the Empire's First Line of Defense

By WALDON FAWCETT

G

REAT BRITAIN, eager to maintain the prestige accruing from her position as the leading naval nation of the globe, is spending annually an immense sum of money in training young men for service in her Navy. Whether the system employed is calculated to give to the naval sailors. of the United Kingdom as perfect an intellectual and physical equipment for their sea duties as is afforded by the methods of some other nations-notably the United States, is a question open to argument, and is to-day a topic of animated discussion in international naval circles. But whatever be its merits or demerits, the British system of training bluejackets is interesting and instructive. Particularly may observation in this field

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THE HOPE OF THE BRITISH NAVY.

Young seamen at physical drill, Portsmouth Dockyard.-The ships here shown are a small portion of the Fleet Reserve.

Stars and Stripes received their prelin- almost absolutely upon the Navy for its inary training as British tars.

food supply. The densely populated islands never have in reserve more than six weeks' food supply; and thus, after all, it is primarily as a safeguard against famine that John Bull maintains at enormous expense a fleet of about half a thousand warships, manned by more than 110,000 officers and men, and in

The First Line of Defense

For a proper appreciation of the importance that attaches to the training of the British bluejacket, it is necessary to bear in mind that for Great Britainwith her world-wide possessions, and

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BRITISH RECEIVING SHIPS, WITH RECRUITS.

The vessel moored in the foreground is the old line-of-battle ship Marlborough. Her amidships and forward decks are housed over for permanent shelter.

dependent, as she is, upon foreign commerce-the Royal Navy constitutes a "first line of defense." For this maritime nation, the sea is not merely a water highway from one country to another, but is in addition a dominion to be policed, patrolled, and guarded. The integrity of Britannia's widely scattered colonial empire, the security of the commerce which is the backbone of her prosperity, and, finally, the safety of the three exposed islands comprising the United Kingdom, all depend upon the mastery of the sea.

The matter is brought home to every British citizen, moreover, by the fact that the country depends, in the last resort,

volving an annual expense of fully $115,000,000 for maintenance and for the new construction necessary to preserve preeminence in naval equipment.

Notwithstanding the immense force of enlisted men necessary to keep in commission a fleet of this size, there has never been a lack of seafaring men to meet the requirements of the Navy. Perhaps this is due in part to the fact that the emoluments, while not comparable with those of the American Navy, are nevertheless quite liberal in comparison with the general British wage scale. The young man entering the British Navy has almost as much chance of promotion as the lad in the American service.

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Trained from Boyhood Beginning his naval career on board one of the training ships stationed at Portsmouth, Portland, Devonport, Falmouth, or Queensferry, the young Britisher qualifies as a "first-class boy;" and is subsequently drafted, after a six weeks' cruise on a training brig and a six months' course on a depot ship, to a coveted place on a sea-going training ship. Here begins his real career in the Navy. If he progresses advantageously, the young man goes in succession through the different grades of "ordinary seaman," "trained seaman," and

INSTRUCTION IN USE OF LEAD AND COMPASS.

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RIFLE DRILL ON SHIPBOARD.

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