pounds of ice in a day of twenty-four hours, even employing water of the temperature at the earth's equator.

"It was next to be ascertained whether the evaporation itself could be made sufficiently rapid. By trial it was found that one superficial foot evaporated, in a partial vacuum, five and a half pounds of ether per hour, even at the low temperature of four degrees above zero. This wonderful result proved that the evaporation, even at such a low temperature, had proceeded three-quarters as fast as that of water in the boilers of locomotive engines on railroads. In this, as well as in several subsequent particulars upon which the entire practical value of the invention depends, it was found that nature, so far from opposing the theory by difficulties in practice, was far more kind than theory, by itself, could have ventured to anticipate.

"Again, it had been supposed, prior to these experiments, that the non-conduction of heat by ice would interpose an impracticability in respect to the enormous surface necessary to freeze water in bulk. It was made to appear, however, that a congelation of one-eighth of an inch in thickness could be realized per hour, and that two hundred and forty superficial feet would be a sufficient exposure for one ton of ice per day of twenty-four hours. It was besides ascertained that the rate of freezing was not appreciably obstructed by the thickness of ice already formed.

"The first attempt at a complete freezing construction was made in the summer of 1850. The machine had only capacity to freeze a pail-full of water at one operation. It embraced the evaporating, the condensing, and the freezing parts of the present engine and apparatus. But the mode of applying the freezing power was widely different. Six months were consumed in trials with this machine, and the most discouraging practical difficulties were brought to light. It was not till long afterwards that the inventor could discover the proper modes of obviating these difficulties. Nevertheless, this first small machine served as a complete verification of the facts, principles, and numerous small experiments which had been relied upon; and it thus became an encouragement, in the end, to attempt a vastly larger construction.

"The present engine was in readiness for a first experiment February 15, 1855. It was calculated to produce two thousand pounds of ice per day in ten freezing cisterns of cast iron, each divided into seven water chambers. With only two cisterns of the ten, three hundred and seventyone pounds of ice were made in eight hours; and, in addition, thirteen hundred pounds of metal were cooled down below freezing temperature; the aggregate result appearing to demonstrate that the machine, with its full complement of cisterns, would be competent to the production of two thousand seven hundred pounds per day, instead of the two thousand for which it was intended. The freezing, however, was too rapid; and the ice, although of fair quality, was too crystalline, as well as somewhat porous. The water employed for condensation was thirty times in quan

tity the water frozen; and both were taken, at temperatures of 70° to 80°, from the hot water well of the steam-engine. The cold current of the cisterns lowered progressively from freezing temperature down nearly to zero; and here it may be mentioned that, as an experiment of mere curiosity, or information, the temperature has at times been made to descend even to twenty-six degrees below zero. In the vacuum vessel the tension of vapor in the above experiment began with 5.7 inches of mercury, and ended with 2.7 inches. In the restorer the tension rarely exceeded two pounds above the atmosphere.

"By a trial, March 2, the product of ice was six hundred and sixtyone pounds in eleven hours ten minutes, with only four cisterns. By computing the aggregate of effect it was demonstrated that the machine could maintain a complement of at least one-third more cisterns than had been originally assigned to it.

"In different trials made during the summer, eight cisterns of the ten were put on. The machine will at any time freeze up in these cisterns fifty-six cakes of ice, each one foot square and six inches thick, and weighing together sixteen hundred and eighty pounds. With ten cisterns a ton could be frozen. This entire effect is produced by a pump of only eight inches and a half bore and eighteen inches stroke, working ninety double strokes per minute, together with small auxiliary pumps for water, ether, &c. In the greatest heats of July the vacuum vessel and the conducting pipes become coated with snow, and clear icicles hang down wherever water drops upon them. The machine has been operated, at different times, for some two years, and no corrosion of the metals has been observed, beyond the ordinary action of the atmosphere. In its operations there is no defect; but there are considerable defects of construction. In this last respect it has, as might be expected, the imperfections of a first machine-offering the experience by which great advantage will be realized in subsequent constructions.

"The ice produced by the above machine is equally sound with natural ice, and, doubtless, equally durable. Probably its specific gravity is even greater, on account of the complete expulsion of air during the congelation, and the consequent absence of air bubbles. It is either glassy clear or pearly white, according to the temperature and other circumstances of the freezing. Experiments, instituted for the purpose, show that these circumstances are capable of complete regulation."

ECONOMY OF PRODUCING ICE BY TWINING'S APPARATUS.

In regard to the economy of manufacture, the inventor presents the following estimates, which, having been made for 1857, may require some modification at the present time:

"The cost per ton of the ice produced is, for any particular locality, a question of mere arithmetic, when the data for calculation are well settled, viz., the price of fuel and of labor, and the scale of the manufac

ture. For a scale of seventy-five to eighty-five tons each twenty-four hours, and wherever coal can be procured at ten dollars per ton, and ordinary labor at one dollar and twenty-five cents per day, the cost will be about one dollar and a half per ton, after the manufacture shall have become settled into its best condition. At first it may be prudent to count upon two dollars to two dollars and twenty-five cents. On a scale of say ten tons per day, the cost may, at first, range as high as three dollars and fifty cents. This inequality of cost is due mainly to the fact that the attendance upon a ten ton engine must be nearly the same as upon one of eight times the capacity. With respect to capital-meaning thereby the entire outlay for the establishment-it will be seen by the estimates given in detail below that a seventy-five ton establishment, in New Orleans, would require about one hundred and fifty thousand dollars. Probably a ten ton establishment, under the same circumstances, would require twenty-five thousand dollars or thirty thousand dollars. Besides its low first cost the manufactured ice will afford several advantages of economy, compared with the imported article. First. Ice houses, except for a few tons capacity, will be dispensed with, as well as the labor of storage and of unpacking. Second. During distribution, or transportation, the cakes will lie packed like cut masonry. Third. The labor, time, and waste of dividing blocks and weighing will be done away with. Fourth. The surplus necessary, in irregular masses, to insure the delivery of full weight, will be saved. Fifth, and most important of all. The distributing carts will load at the manufactory; so that the article, delivered as just made, may unite the profits both of the present importation and, in a large measure, of the present distribution, still underselling the present market.

If the foregoing statements are well established, it is obviously a settled fact that the warm climates of our country are soon to be supplied with artificial ice by means of this invention. How much further this assertion might be justly extended is immaterial at present. Evidently where the demand is most urgent the supply should first be provided."

Professor Twining prepared, in full detail, estimates of the cost of erecting in a great city, say New Orleans, a manufacturing establishment, capable of producing eighty tons of ice per day. The amount of capital which would be required for the creation of such an establishment with its machinery complete, and including the cost of building and grounds, he concluded would not exceed one hundred and sixty thousand dollars. The daily expense of maintenance, including fuel, wages, repairs of machinery and building, oil, ether, and all contingencies, he computed at one hundred and twenty dollars. If to this we add interest at six per cent. on the investment, amounting to twenty-six dollars and thirty cents, the total cost of eighty tons would be one hundred and forty-six dollars and thirty cents, or one dollar and eighty-three cents per ton. It was a large allowance for waste and expense of distribution, therefore, when the inventor assumed, for purposes of comparison, the

total cost to the producer at five dollars or six dollars per ton, in the following statement of conclusions:

"The first cost of ice to the retailer in New Orleans at the present time-including waste and expense of distribution-is variously stated at ten dollars to sixteen dollars per ton. The same, under the new system, would be five dollars to six dollars. Ice, in that city and in most other southern cities, commands readily from twenty dollars to forty dol lars. It is quite safe, therefore, to put the profit upon the manufactured article ten dollars per ton. Supposing then, at first, eighty per cent., or more, of the profits appropriated to reimburse the capital, principal and interest, and then, when the establishment has cost the capitalist nothing, the profits thenceforth to be divided equally between the capital interest and the patent interest, the foregoing data make it obvious that a very unusual margin of profits on the original investment is exhibited, even though that investment is already repaid."1

It cannot be too much regretted that an invention of such merit and importance, and of which the soundness and commercial value had been so fully demonstrated, both theoretically and experimentally, should, through the apathy or timidity of capitalists, have been permitted to lie neglected in the country in which it originated, till foreign enterprise had seized upon it, and developed it into a great industry.

1 In the American Journal of Science and Arts for 1850 will be found two papers by Dr. John Gorrie on the heat developed by the compression of air. These papers are in substance a resumé of the results obtained by him in a series of experiments conducted on a large scale at the instance of some capitalists of New Orleans, who had in view, as he says, a commercial object-probably the manufacture of ice. These persons may have been the same by whom the enterprise spoken of in the text was set on foot. Dr. Gorrie writes under the impression, natural at that date, that the freezing effect of the dilatation will be equivalent to the heating effect of the compression. He endeavors, by the discussion of the results of his experiments, to ascertain the law which governs the relation between pressure and the ultimate temperature-a law which Poisson, however, had already established, and which it would be somewhat difficult to discover by methods entirely empirical. The experiments of Dr. Gorrie have a certain practical interest; but the progress which has been made within the last twenty years in the science of thermotics deprives them of value considered as contributions to theory.

CHAPTER XIII.

LIGHT-HOUSE ILLUMINATION.

DISPLAY OF OBJECTS CONNECTED WITH THE CONSTRUCTION AND OPERATION OF LIGHTHOUSES-MODELS OF ENGLISH LIGHT-HOUSES-USE OF THE MAGNETO-ELECTRICAL MACHINE-WIGHAM'S GAS-LIght for ligHT-HOUSES-THE GAS-LIGHT COMPARED PHOTOMETRICALLY WITH THE LIGHT FROM COLZA OIL LAMPS-THE BAILEY LIGHT-HOUSEFLASHING LIght at WickLOW HEAD-REPORT TO THE BOARD OF TRADE UPON THE RELATIVE ADVANTAGES OF GAS AND OIL FOR LIGHT-HOUSE ILLUMINATION-LETTER TO ADMIRAL SHUBRICK-ELECTRIC LIGHT-Light AS PRODUCED BY BATTERY-BY MAGNETO-ELECTRIC MACHINE-Regulators of ELECTRIC LIGHT--The BRITISH MAGNETO-ELECTRIC MACHINE IN THE EXPOSITION-THE FRENCH MACHINE-ECONOMY OF THE ELECTRIC Light-The electric lIGHT AT LA HÈVE-FOG PENETRATING POWER OF THE ELECTRIC LIGHT COST OF MAINTENANCE AT LA HÈVE-LADD'S DYNAMOELECTRIC MACHINE-MAGNETO-ELECTRIC MACHINE OF DR. WERNER SIEMENSWILDE'S MACHINE-EXPERIMENTS AND APPARATUS OF MR. C. W. SIEMENS AND OF PROFESSOR WHEATSTONE-ADVANTAGES of Ladd's MACHINE.

It is not designed under this head to pass in review the various interesting objects connected with the construction and operation of lighthouses which were brought together in the Exposition by the governments of England and France. The display made by these two great nations was exceedingly comprehensive in its extent and admirable in its character, well worthy indeed of the prominent position occupied by those nations as maritime powers. France exhibited not only every description of optical apparatus for illuminating light-houses, but also models and drawings of light-house towers, and even the real towers themselves. One of these, a beautiful iron structure, fifty-six metres high, (more than one hundred and eighty feet,) crowned with a revolving light of the first order, was constructed for the Roches Douvres, a reef off the north coast of Brittany, where it is to be placed after the close of the Exposition. Another was presented as an illustration of the form of the French harbor light-houses, and was only eight metres in height. Both the French and the British governments exhibited electric lights, the brilliancy of which, especially of the former, excited great admiration. The models of light-houses exhibited by England were particularly interesting. There were fifteen of these, presenting on a reduced scale not only the towers themselves, but also fac-similes of their sites and of the surrounding topography. There was also shown a model of the lightship at the Goodwin Sands, one side of which had been left open to exhibit the arrangements of the interior.

The exhibition of light-house apparatus, however, complete and interesting as it certainly was, presented little that could be called new. The most important improvement made in the system of sea-coast lighting in