nometer, and in a few moments the column dropped away from the sphere. This occurred twice, when I concluded that it must cool more slowly, so left it in the boiling water, to cool with it. This produced the desired result, and the hot side became perfectly restored. On the cold side I substituted a mixture of ice and salt, in which I placed the bulb, and with an ordinary cologne spray-bottle, substituting sulphuric ether, threw a spray on the bulb, which acted as did the steam. I was compelled to leave the instrument to warm gradually in a vessel of icewater, and in an hour had it in good working order.

I send herewith a set of diagrams of the curves produced by the dif ferent baths tabulated, and am,

Very respectfully,

Prof. S. F. BAIRD,

L. A. BEARDSLEE, Commander, United States Navy.

United States Fish Commissioner.

To ascertain the correctness of the standard used in the foregoing experiments, it was tested in the apparatus provided by the Signal Corps for testing thermometers-simply a tin can with a perforated tin false bottom about midway of its height to permit the leakage from the melted ice to escape.

A thermometer manufactured by Tagliabue for the Commission, with cylindrical bulb 14 inches long and in diameter, graduated from 30° to 1400, on a scale of 85 inches, was compared at the same time. The bulbs were immersed and packed snug in pounded ice. The Tagliabue recorded 310.6, and the standard 320.05. The experiment was repeated with the same result.

Respectfully,

L. A. BEARDSLEE,

Commander.

WOOD'S HOLL, September 23, 1875.

An additional set of tests were made with the Cassella-Miller thermometer in use this summer at Wood's Hole (No. 1,844). They were made with the utmost accuracy possible, with the same standard in use last summer, and the aquarium. They have developed the reason of the anomalous action of the thermometers in ice.

In test No. 1, in ice, the instrument was placed on its back in a trench cut in the ice, and the bulbs covered with pounded ice. The mercury corresponded in its action very closely to the action of a bath of 50° until it reached that point.

In test No. 2 the upper portion of the ebonite guard was removed, thus letting the crushed ice come into immediate contact with the upper

portion of bulbs. This induced quicker action, but still slower than a bath of 350; and at last, as in former cases, the mercury apparently ceased to fall at 35°.

This experiment is put in simply for the purpose of guarding other experimenters against the mistake.

The standard, as in last year's tests, did not vary from 320.05.

Respectfully,

L. A. BEARDSLEE, Commander, United States Navy.

XX.-ON ARTIFICIAL REFRIGERATION.

BY JOHN GAMGEE, LONDON, ENGLAND.

A.-INTRODUCTION.

Ice, water, and steam, strikingly exemplify the nature of changes, or the different physical states, produced in matter by heat. Ice is a transparent or translucent solid, which melts into water on the addition of 142.66 heat units (Regnault). This water has to be raised from the nor mal temperature of melting ice, viz, 320 Fahr., to 2120 to boil, and every pound converted into steam absorbs 965.7 heat units, without affording thermometric indications of the change. The heat is said to have become latent, but it is lost in molecular motion.

The latent heat of water is higher than that of any other agent, and a great depression of temperature ensues when, from a limited amount of water, vapor promptly rises. Thus, water placed in porous earthenware vessels, which are protected from active surface air-currents, by being placed in shallow pits, freezes in Bengal. Windy nights in summer are unfavorable to the process. It is on still and cloudless nights that active radiation, into open space, favors the crystallization of the water.

Probably with the ice thus formed and the efflorescent salts at hand, the Hindoos first attempted artificial refrigeration. Nitre-the sal petræ of Geber or nitrum of Albertus Magnus-was regarded by the ancients as the primum frigidum, the cold element of the earth. It occurred on the borders of the Ganges, in Ceylon, and elsewhere as a natural surface deposit, and, after the rainy season, a crust one-third of an inch in thickness may be gathered from the ground. It is dissolved out of the saltpetre earths, which at Tirhoot, in Bengal, contain from 8 to 9 per cent. of pure potassium nitrate. The mercury descends 18 or 20 degrees if a thermometer be plunged into water simultaneously with nitre. Mixed with ice, a temperature between 5 and 6 degrees below 32° Fahr. is obtained; and we learn, that as early as 1550, the Roman nobles cooled their wines by a mixture of snow and nitre. This frigorific mixture is mentioned by Latinus Tancredus, a professor of medicine in Naples, in his work De Fama et Siti, published in 1607. Villa Franca, a Spaniard, had been credited with the invention, but in all probability the practice was derived from Asia, and popularized by the Portuguese after the first discovery of India. Common salt and ice were adopted by Fahrenheit as the means of obtaining the temperature 0 of his thermom

eter, and this mixture was widely known to the learned throughout Europe. In Southern Italy it was used for cooling lemonades, and from thence, in the middle of the seventeenth century, sprang the Paris “limonadiers," as well as the preparation of flavored ices and creams, the gelati and sorbetti of the Italians.

Neapolitans and Swiss Italians have remained preeminent in the management of cafés and the preparation of iced confections. They estab lished themselves early in all the large cities of Europe. It is but recently that an Italian Swiss, by the name of Carlo Gatti, died wealthy and esteemed in London. He was the first practical introducer of icecreams to the British public. His stall stood forty years since in Hungerford fish-market, and he himself has informed me that, in his early days, he had great difficulty in inducing people to appreciate his gelati. He walked about the market with a glassful of ice-cream, and offered spoonfuls to passers-by until they began to acquire the taste for and recognize the wholesome character of cold delicacies. They dreaded them as much as the Brazilians have dreaded ice until recently, being regarded as productive of serious illness. Gatti not only introduced his ice-creams, but did much to popularize the use of ice in London, and to the last he retained a large share of a trade, greatly encouraged by his discrimination and integrity.

In Gatti's early days, Thomas Masters published his Ice Book (1844), which contained some interesting historical data, though the work appeared to advertise patent ice-cream freezers, knife-cleaners, &c. It tended to make the use of ice popular, especially among the rich; and, the growing wants of the metropolis, compelled fishermen to use more and more ice year by year.

The growing wealth of British cities, the facilities for the transport of fish by sea, and a wider appreciation of wholesome fish food, drove the trawlers further and further, year after year, seeking fresh ground and using more ice, the greater the catches and the longer the distance of the fishing-grounds reached from shore. An enterprising firm, of late years organized as a limited liability company (Messrs. Hewett & Co.), established a fleet of steam carrying vessels as their fish business grew.

The steamers are small and carry about 35 tons of ice each, some more, some less. Were they larger, the difficult process, of transferring the fish from the boats, would be attended with even greater danger than it is at present. The steamer is small enough to drop into the trough of the sea with the boat, and the two hug each other, without danger of a crushing collision.

It is in this way that England, and especially London and the fishingports of Great Yarmouth and Grimsby, have become the centres of a very extensive and lucrative ice-trade from Norway. In the early days of the British ice-trade a company was formed to import ice from the New World, and "Wenham Lake" ice became the staple and favorite brand.