CHAPTER XXXI 

THE FAMOUS EQUILIBRATOR 

     An important, and as it turned out, a crucial part of our equipment, was the equilibrator. So much has been written and said of it, and there has been so much misapprehension concerning it, that I shall try to explain with the utmost clearness its purpose and function, though the reader who has attentively gone through the preceding chapters doubtless understands it very well now. 

     As I have already pointed out, an equilibrator, or some other device that performs the same function, is an absolute essential to a long voy­age with a motor-balloon. The purpose of this auxiliary, it is well to say at the outset, is not to keep the airship from going high in the air, but to prevent it falling into the sea. For a long voyage one must reckon upon remaining six to ten days in the air. That is the time we calculated would be necessary for crossing the Atlantic. 

     Now, with the lower temperature of every night the gas cools and contracts, thus diminishing the volume of gas in the balloon. Air must be pumped within the interior reservoirs or bal­loonets so that the balloon part of the airship may preserve its form. Air weighs about 1.2 ounces per cubic foot. The more air pumped in, the heavier the contents of the ship. But, so far as the buoyancy or lifting force of the balloon is concerned, it makes no difference whether air is or is not injected. With air pumped in, the contents of the balloon have greater weight. Without air in, the balloon, shrinking with contraction of the gas, displaces just so much smaller volume of air, and there­fore lifts just so much less. It is as broad as it is long in its effect upon the lift of the ship. In other words, the volume of air which equals the shrinkage of gas weighs the same whether it is within or outside the balloon. But it is nec­essary to put air in so that the form of the bal­loon may be preserved; and this is necessary to keep down resistance and to make sure that the suspension works normally. 

     When the gas contracts during the night and the balloon loses lifting force it is obvious the airship will go down into the sea unless the load carried upon it be diminished to the extent of the lost buoyancy. Without an equilibrator, this weight must be thrown overboard—sand, or water, or gasoline, or something. Once over­board, it is lost, and cannot be recovered. If you must repeat this process of lightening ship by throwing over ballast every night you are out, it is apparent that for a long voyage the total weight to be carried for this purpose rises to high figures. 

     But with an equilibrator, or trailing device, instead of throwing ballast overboard, you per­mit your trailer to descend upon the surface of the sea and float there. The ship is relieved of that much load, but the ballast is not lost; it may be used over and over again. The same weights used Monday night to lighten ship are used Tuesday night, and Wednesday night, and so on throughout your voyage. Moreover, these same weights are useful during the day to pre­vent the ship going too high when under the hot sun the gas expands, lifting force rapidly increases, and the ship rises. As she goes up she must lift more and more of the trailer and thus take upon herself more and more load. 

     As already explained, I had suggested and experimented in the polar regions with devices built to serve this function. The first equilibra­tor for use in the Arctic was a series of steel reservoirs or tanks. Then we tried the leather serpent in two voyages, with the results described in previous chapters. For the transatlantic trip we came again to the steel tanks. 

     This latest equilibrator consists of a series of steel reservoirs, each about four feet long and nine inches in diameter. 

     Each reservoir has a tube lengthwise through its center, and all of them—there are thirty in all —are strung upon a staunch steel cable passed through these tubes. Each reservoir is concave at its forward end and convex at the other, so that one fits into the other like a cup joint, which is padded with felt to take up shocks and prevent wear and abrasion. A special clamp holds each tank to the cable at the required place, and the cup-like joints give to the series great flexibility and ease of adaptation to the surface of the sea waves. 

     All of the reservoirs are filled with gasoline, and each tank and its contents has a weight of about 100 pounds. Gasoline is not put here be­cause we wish to carry fuel in this manner, but because the equilibrator, "to be effective for the purpose for which it was designed, must have a certain weight, and it is far better to have that weight made up largely of a useful material rather than of such dead weights as steel or wood. 

     The whole is so arranged that after the gaso­line carried in big steel tank of the car shall have been exhausted the reserve supply in these reser­voirs becomes available, one tank after another being lifted up to the engine room and its con­tents utilized in the motors. 

     Before we set out upon our voyage across the Atlantic, I wrote as follows concerning the equil­ibrator: 

     "The reader will readily understand the pur­pose for which this strange device was con­structed. More than 300 feet in length, with a total weight of nearly two tons, its lower end will ride upon the surface of the sea. This lower end is composed of forty solid wooden blocks tapering to a very small diameter, much like the tail of a snake. 

     "The wooden blocks, and the steel tanks as well, are buoyant and flexible, and the whole will swim in the wake of the America, partly upon the surface of the sea, partly lifted in the air—a giant steel sea serpent with a wooden tail, its head erect, and making for Europe as convoy of the first ship of the air ever seen over the waters of the broad ocean. 

     "Suppose half of our great snake of steel, his belly full of gasoline, is upon the water, and half in the air. Night comes on; the gas cools; rain falls; the conditions already described are upon us; the America droops more and more to the sea. As she goes downward one after the other of the constituent steel tubes of the serpent is deposited upon the surface of the ocean. For every four feet of descent the ship is relieved of 100 pounds of weight plus the slight weight of the cable; and this continues until she is again balanced in the air, perhaps the greater part of the equilibrator now floating along behind us. 

     "In the morning the sun rises bright and hot. The reverse process follows—the expanding gas sends the ship upward. As she rises one after another of the steel reservoirs must be lifted from the sea, 100 pounds more weight upon the ship for every four feet of her ascent. 

     "Thus the steel serpent becomes an automatic governor upon the upward and downward move­ments of the ship due to meteorological changes. Hence the name 'equilibrator,' or `stabilizator.' The huge snake and its valuable stuffing is really ballast which may be used over and over again without ever losing it. 

     "It is unnecessary to carry sand or water to throw overboard. Our serpent, if he behaves as well as a well-made reptile ought, should hold the America at an altitude of from 150 to 250 feet above the ocean, save us ballast—which means fuel—on one hand, save us gas on the other, and enable us to prolong the voyage from the forty-eight hours practicable without a ser­pent to the seven or nine or ten days which may be required for crossing the Atlantic. 

     "How will this equilibrator serpent work in the rough sea? We confess we do not know. We believe—but are not quite sure—that it will be so 'soft' upon the waves as to give us little trouble in the way of shocks or jerks upon the airship. We have tried the same principle over the Arctic Sea, and there the device rode smoothly, and being a continuous body made no considerable resistance of the progress of the ship towing it. 

     "But the Arctic waters were not rough, and we are very curious as to how our new and improved sea serpent will behave upon the Atlantic. Will he serve or sting us? At any rate, a voyage of 3,500 miles by airship is impracticable without the aid of some such device; and this one is the best we can do out of our experience and study." 

     According to the original plan, only a small part of the serpent was expected to float upon the surface of the ocean. In other words, under normal conditions the lower end of the tail—a few of the wooden blocks—was to be skimming the crest of the waves. Or, the trailer might be entirely out of water. It is always easy to prevent an airship going high. That is done by simply pulling the valve and letting out a little gas. This is not an unnecessary loss of gas, be­cause with a hot sun the gas will expand and a part of it be lost, anyway; and by keeping the ship down to a low level we avoid the further loss of gas which comes from the expansion due to diminution of atmospheric pressure as you as­cend from the surface of the earth. This loss is very great. 

     At the level of the sea the normal pressure of the atmosphere is 760 millimeters (29.92 inches) of mercury. If you ascend 1000 meters, or 3,280 feet, atmospheric pressure drops to 670 millimeters (26.38 inches) of mercury. In other words, the pressure of the air upon all the sur­face of a balloon or airship is reduced in the proportion of 90 to 760, or nearly one-eighth, and, assuming that the temperature remains the same, you have therefore lost nearly one-eighth of all the contents of your balloon from this cause alone. 

    The valves of your balloon are set by springs to open automatically at a certain pressure. The first to open, because set for a smaller pres­sure, are the air-valves. And if there is that much air in the inner reservoirs, an airship of the size of the America would lose 43,000 cubic feet of gas from diminution of atmospheric pressure in taking an altitude of 3,300 feet, and the weight of this volume of air is 3,225 pounds. This is precisely what happened to our airship the third day of our voyage over the Atlantic, when the ship took an altitude of about 3000 feet, lifting the equilibrator and all high in the air, due to sun heat and expansion by altitude. 

     We realized from the first that to have a ser­pent weighing 3750 pounds all the time trailing in the sea would retard the progress of the air­ship, probably interfere seriously with her steer­ing, and by its drag-effect and its leaping from wave to wave in heavy seas tend to strain the airship and pull it down toward the surface of the ocean. All this we knew nearly as well be­fore the voyage as we did during and after the voyage. For the equilibrator we have been much criticized. 

     But we never intended to use it the way in which it was used. We had planned to start the voyage with not more than one-half of the equili­brator upon the surface of the sea-1,500 to 1,800 pounds. Each 24 hours we reckoned to lift 500 or 600 pounds of this on account of burning so much gasoline in the motors. If this plan could have been carried out, the serpent would not have interfered with the successful navigation of the airship. The small part of it down upon the sea would not have given us any trouble, or very little. And after the first day the equili­brator would have worked precisely as it was designed to work—that is, carried chiefly in the air, suspended vertically, as a reserve weight to be used in keeping the airship from going down to the ocean whenever the cold or other condi­tions greatly diminished the lifting force of the balloon. 

     Circumstances which we could not control changed this plan materially and unfavorably. I shall tell frankly what these circumstances were.