plain brute strength, and such crude devices as the men of that age could improvise. With equipment of the type we are using at Panama, the Chinese might have inclosed their whole empire.

The Great Wall extends from the coast along the northern boundary of what was ancient Cathay to the westernmost province. Since the acquisition of Mongolia, the stone barrier stands as a grim relic almost in the center of the Empire. There are several arms or branches to the wall. One of these runs east and west just north of Peking, while the main arm to the coast extends some distance still further north from the capital. It extends for hundreds of miles into regions where all sorts of conditions are to be met. It wends its serpentine way across barren deserts, mountains, and lowlands-now and then making a break for rivers crossing its path. One of these is a twin, or double river, for many miles, and it is said that it has changed its course nine times in two thousand five hundred years.

China is notorious for her lack of roadways. Even to this day the remote regions can be reached only on camels or by boats towed up stream, for hundreds or thousands of miles, by

men running along the banks. It is claimed by some that the top of the wall was used as a thoroughfare, especially during the construction. At places on the southern side of the wall, graded inclines are built to the summit. These might have been used for driving beasts of burden to the top of the wall for trips up and down the length of the structure, while the work was under way.

The wall is not high. In places an American athlete might clear it with a vaulting pole were it not for its unusual thickness. At regular intervals. are formidable stone towers. Here no doubt the commanders of the defending legions took their stations when invaders came from the north.

Undoing a task sometimes takes as long as it does to do it. It took many years to build the Great Wall. If China ever undertakes to tear it down in order to meet the ideals of a progressive republican government, the job will be no child's play. But with a railroad on either side of the "fence", and batteries of stone-devouring steam shovels going night and day, the engineers might succeed in destroying in a day portions that it took years to build when the world was younger.

T

HE menace of the torpedo and the dangers of grounding have been greatly minimized by a strikingly ingenious self-salving system which the Navy Department is now installing upon the biggest of its battlecraft. Within some limits, this installation is substantially making these ships unsinkable, and even the casual layman will grasp a fair share of this significant departure in naval archi

tecture.

Commonly, we speak of this era of ours as the age of electricity, but we have another inexhaustible source of energy which, in its way, is accomplishing marvels: this is compressed air. It is this medium which the Government will rely upon hereafter in keeping its fighting giants afloat after they have been grievously wounded below the waterline through one cause or another. It is not only that these vessels shall be kept from foundering merely because of the money outlay they represent, but because of their vital importance to the maintenance of

the peace of our homes as well as the safeguarding of the many hundreds of lives they carry.

Let us start out in the telling of our story by describing a simple experiment which will give you the basic principles upon which this air pressure system, in its several applications, works. The diving bell is a virtual counterpart of an inverted tumbler submerged and so arranged that air pumped down through its top-which would be the normal bottom of the tumbler-gathers inside of it until the pressure of that confined air slightly exceeds that of the enveloping and intrusive water. When this state is reached, the sea is forced out, and it will remain excluded as long as the pressure of the atmosphere inside of the diving bell balances that of the hydrostatic pressure without. You can prove this by taking a tumbler, boring a small hole in its bottom, and connecting thereto a tube of any sort and sealing it with wax so that the joint will not leak.

In effect, this is broadly what is

being done to the water-tight compartments of our fighting ships, so that if the bottom plating becomes torn or ruptured, each wounded division can be quickly turned into a more or less perfect diving bell, depending upon the nature of the injury. The system is the invention of W. W. Wotherspoon, who has turned his engineering experience as a sand-hog into a number of novel directions. One of the admirable features of Mr. Wotherspoon's selfsalving installation is that it largely utilizes existing facilities which are of necessity built into the modern man-o'war. His ingenuity lies in great part in putting these existing apparatus in the way of doing a vitally helpful service in an emergency involving the menace of foundering or the dreaded hazards of fire. From the keel up to a considerable height above the waterline, every compartment of that great steel honey-comb is designed to be watertight, and in order to ventilate these divisions properly and to prevent the accumulation both of foul air and possibly explosive gases, an extensive system of piping carries fresh air by one line and draws off the tainted atmosphere by another.

These pipes are the conduits by which Mr. Wotherspoon leads his compressed air into the various compartments. The source of supply of this air is the compressors with which every fighting ship is equipped for other necessary services. All that is required is a flexible connection which can be quickly adjusted for the purpose of leading the air from its source of supply into the pipes normally intended for ventilation only.

Suppose that the ship has hit a rock and the bottom plating has been torn open throughout one of the compartments. Instantly, the sea rushes in and fills the space, and unless the envel

oping structure is especially strongwe have learned too forcibly how this is not always the case -the bulkheads and the overlying deck slowly yield and other chambers become flooded, and the vessel is drawn irresistibly further and further into the greedy grip of the

waters.

Now what happens under these conditions when a craft is equip

All of this piping is made watertight where it passes through decks or bulkheads, and it is tested to withstand hydrostatic pressure equal to the worst to which it might be subjected if the vessel were partly flooded and deeply settled below the normal load-line.

Wotherspoon's self-salving ap

paratus? Immediately, the connection is made between the compressors and the ventilating pipes and air is directed not only into the compartment damaged. at first hand, but into the surrounding and neighboring subdivisions of the ship, and here is where the cunning part of the system manifests itself. Mr Wotherspoon distributes his air pressure so that the damaged space is filled with the heaviest pressure, those

contiguous are filled with the next. lower pressure, and the next series of surrounding divisions are charged with a still lower pressure.

Without going into figures, it is enough to know that the steel structure lying between these succeeding pressures is at no time subjected to a greater pressure than that of the difference between the two. In other words this is a matter of only five pounds to the square inch, and is really less than the maximum bursting pressure the bulkheads and decks are designed to withstand. The net result of this is that the surrounding structure absorbs the stresses and unites in sustaining the damaged compartment in its battle with the intrusive sea.

All, therefore, that is necessary is

a proper condition or to detect weaknesses and to correct them at once.

A natural development of this waterexcluding installation is its adaptation. for the suppression of fire. Instead of turning compressed air into the affected compartment, as we have described, a non-combustible gas is pumped into the space where the conflagration is. This gas simply smothers the flames, chokes out the fire, and prevents its spreading. Ordinarily, a compartment afire would be flooded with water and so, too, adjacent compartments would be filled. This might involve the needless injury or destruction of stores and valuable property. By Mr. Wotherspoon's system, however, these losses are reduced to a minimum-the gas will not harm, and

that the air in the damaged area shall be equal to the highest pressure of the outlying water or just a wee bit in excess in order to keep the latter out from the underside of the overlying deck down to the uppermost edge of the hole. To increase the air pressure after that would be useless because the air would then escape outboard and perform no useful service.

A very valuable feature of this equipment is that compartments can be tested at any time for tightness by using air instead instead of water, which might damage stores and electrical and other apparatus. The hissing air, too, will tell just where the leak is. This will enable a commanding officer at all

the only damage would be that due to the fire before it is suppressed. The first of our ships to be experimentally equipped in this manner was the North Carolina. Our dreadnought, the Delaware, is the first ship since to receive this installation, but all of the latest of our battlecraft under construction now will be so safeguarded.

The logical outcome will be that seagoing passenger ships will be made less likely to sink by the adoption of this means of self-salvage. Of course, it is not likely that merchant craft will go in for this upon the extensive scale employed upon big naval vessels, but a modification would be ample to make quite unlikely a disaster like that of the

A

T the present price for silver-black fox skins a man possessing a source of supply would become a millionaire in a few years. Here, therefore, is a real legitimate "Wallingford" enterprise which opens a field of industry that seems destined to become one of the best paying businesses on the North American continent. The scheme is nothing more nor less than the raising of silver-black foxes, and it has reached the stage where it may be regarded as an addition to the already long list of occupations.

The scene of this new gamble is Eastern Canada, and it beats the mining game for excitement. Fox raising has become a craze; men of wealth are heavily concerned in it, and the little fellows are trailing along, hoping for some of the crumbs.

The Province of Prince Edward Island, which has long had the name of the "Garden of the Gulf", and has been famous for its oats, has been turned practically into one vast fox ranch, and land in Nova Scotia, New Brunswick, and Quebec is being requisitioned for the new venture. The final object of it all, of course, is to market the pelts, but no

one has dared to kill a fox for market in the last two years. The world record price for a silver fox skin is $3,000, whereas the last recorded price for live silver foxes was $30,000 a pair.

Aside from the beauty of the silverblack fox fur, its rarity has helped to keep the price up. The market reports show that the average production for the past ten years has been less than one hundred pelts a year, and many of these skins have been imperfect. The problem, therefore, for raising and breeding in captivity such valuable animals is one that has exercised the mind of many an expert trapper and student of the wild. Owing to their extreme sensitiveness, silver foxes are very difficult to rear, notwithstanding their hardiness.

A perfect skin has a foundation of jet black, with a sprinkling of hairs on the back and rumps which are silver gray for a portion of the distance between the root and the tip of the hair. The extremity of the tail is always pure white. The brilliancy and sheen of a fine pelt give it a notable richness. In fact, it has been estimated by furriers that if black fox skins were as plentiful as those of the red fox, they would still command