Eustis, was in the printer's hands, and would probably be finished in a few weeks.

Mr. Charles Jackson, Jr., in reference to the discussion at the last meeting on the Ericsson engine, said that the calculation showed that the efficient pressure was three fourths of a pound per inch in the up stroke, and nothing in the down stroke, or three eighths of a pound average. He did not believe this was enough to overcome the mere friction of the engine, and thought there must be an error in the facts on which the calculation that gave the result was based. He believed the air-engine, working at about 500°, and cutting off at one half or two thirds of the stroke, would give the same result as a non-condensing expansive steam-engine working with fifteen pounds of steam.

Steam at that pressure having about the same weight as common air, but the latent heat of the steam being twice the 500° the air required, and the capacity of water for heat being nearly four times that of air, the steam-engine required eight times as much fuel as the air-engine did. Half the power of the air-engine would be used in working the supply-pump, leaving the air-engine still four times better than the steamengine even without any regenerator. The amount of heating surface required would be a great deal less with air than with water. In hot-blast iron smelting-furnaces which he has observed, there was five times as much air heated to 600° as there was water boiled off for the engine, and yet the hotair ovens did not occupy one tenth of the room the boilers required.

Professor Treadwell remarked, that it was a matter of every day's observation, that in regard to the heat-conducting surface of iron necessary with air and with water, the advantage was very much in favor of water, even twenty to one.

Professor Peirce reaffirmed his statements at the preceding meeting, with a few modifications, not changing his general results. He said that accurate measurements by the Coast Survey showed that the actual speed of the Ericsson was only

seven miles an hour, which, compared with the speed of the Collins steamers, would make the Ericsson consume twentyfive per cent. more fuel than the latter.

At the former meeting he had not considered the "cut-off," which gives a result more in favor of the Ericsson; though this advantage is compensated by the error he made in favor of the Ericsson engine by taking the heat of the cylinders at 480, whereas the actual heat used was only 384°. The "cut-off" may be so short that the regenerator would be useless, the air going in and out at the same temperature, though more fuel would be required in this way. The shorter the "cut-off," the greater would be the theoretical power, provided you could get the air in. The "cut-off" in this engine is at three fourths of the stroke; for one fourth of the stroke there would be a pressure of three fifths above an atmosphere, and for the other three fourths of the stroke only one fifth above an atmosphere. One pound pressure would be required to force the air out through the wire-gauze, instead of the halfpound previously mentioned; and one and one fifth pounds pressure to force it in.

Dr. W. F. Channing remarked, that the difference in the loss of power from paddles entering the water (which is great in steam-vessels), and the less amount of friction, give more power to this engine. He thought, that, deducting one pound pressure (necessary to force the air through the wire-gauze) in place of half a pound allowed by Professor Peirce, there is a pressure of only one fourth of a pound left; and deducting from this 40 horse-power (equivalent to two fifths of a pound pressure, by Professor Peirce's calculation) for the loss from the paddles entering the water, and one fifth of a pound of pressure for additional friction, there would be a pressure of minus seven twentieths of a pound to an inch inside the cylinder, or, in other words, that the engine was worked by an outside atmospheric pressure acting inwards.

Professor Josiah Parsons Cooke and Professor Joel Parker of Cambridge were elected Fellows of the Academy; the

former in the section of Chemistry, the latter in the section of Philosophy and Jurisprudence.

Three hundred and seventy-sixth meeting.

March 1, 1853. MONTHLY MEETING.

The PRESIDENT in the chair.

The Corresponding Secretary announced that he had received a letter from Professor Parker accepting membership of the Academy. Professor Cooke took his seat as a Fellow.

Professor Treadwell observed, that the speed of the Ericsson in her trip to Washington was about six geographical miles an hour. He mentioned that hundred-gun ships, of a model far inferior to that of the Ericsson, had made nearly twelve miles an hour in trial trips in England, with steam-engines of 350 and 400 horse-power; as this was twice the velocity of the Ericsson, the power required would be eight times that of the Ericsson, which was far from the power used. The Ericsson consumed five tons and a fraction of coal a day; to get double the velocity, as in the English vessels, supposing the resistance the same (which it is not, on account of the vastly superior model of the Ericsson), about forty-five tons would be consumed, which is more than was consumed by the steam-vessels above mentioned. So that the experiment, after all, does not promise much in favor of the caloric engine.

Dr. W. F. Channing observed, that it is admitted that there is a saving of about one third of fuel in the caloric engine; that it must be an important improvement for stationary engines, even if it should not be found compact enough for seagoing vessels. An article in the Scientific American gives to the Ericsson 250 horse-power.

Professor Treadwell remarked, that very nearly as much power could be obtained from the amount of coal used by the Ericsson, if employed in the generation of steam, on account of the far greater expansive power of the latter.

Mr. Charles Jackson, Jr. said that actual experiments by the thermometer have proved that 360° of heat are saved by the regenerator, there being only 30 difference between the temperature of the air going out and that going in.

Professor Gray alluded to a very interesting botanical discovery in this country, namely, the finding of two species of Trichomanes in the northwest corner of Alabama; species of a group of ferns, of very delicate texture, usually confined to very moist parts of the tropics, or to islands having a damp climate and equable temperature, but not before known to occur within the limits of the United States.

The small species of Trichomanes exhibited by Dr. Gray is doubtless a new species, which he proposes to name T. Petersii, in honor of the discoverer, T. M. Peters, Esq. The other is the Trichomanes radicans, found in the southwestern parts of Ireland, and also widely scattered in the tropics. Dr. Gray mentioned that the latter is very frequently cultivated in the glazed cases invented by Mr. Ward; without such treatment it is incapable of cultivation.

The wide range of the ferns having been alluded to, a discussion arose on the difficult question of specific characters. Many supposed identical species of animals have been found, on close examination and actual comparison, to be different; and it was questioned whether the same may not be true of the cosmopolite ferns.

Three hundred and seventy-seventh meeting.

April 5, 1853. MONTHLY MEETING.

The PRESIDENT in the chair.

Professor Horsford made some remarks explanatory of a part of the fourteenth chapter of Leviticus, in which are described the signs and treatment of "leprosy" in a house.

He alluded to the decomposition of sulphate of iron when subjected to decomposing animal matter, and its change into the sulphuret or iron pyrites. This last oxidates readily, and

is one cause of the stains and some other injuries often seen in stones used for building purposes. He mentioned several buildings which had thus been disfigured, and remarked that the Washington Monument would, in course of time, be defaced from this cause.

The leprosy is described as being "in the walls of the house, with hollow streaks, greenish or reddish, which in sight are lower than the wall." And the remedy is given, the removal of the affected stones, their replacement by others, and the scraping and plastering of the house.

He thought that the "leprosy of the house" alluded to, was caused by the decomposition of this salt of iron; the greenish color being due to the presence of the sulphate, and the reddish to the peroxide of iron. The limestone used for building in that locality he had found to contain iron pyrites.

He also alluded to a leprosy in clothing, arising from a spontaneous change in the improperly cleansed wool from which they were made.

Dr. Bigelow, after alluding to a supposed connection between leprosy and this change in the walls of a house, observed that the cause of epidemics is completely unknown, and that the reference of them to specific causes has always been in proportion to the ignorance of the people.

Professor Jeffries Wyman made a verbal communication on the effects of physical agents on the development of life. He had repeated some of the experiments of Milne-Edwards on the influence of a low temperature and the absence of light on the development of frogs.

The tadpoles experimented upon were those of the common bull-frog (Rana pipiens, Linn.). These, under ordinary circumstances, are hatched in the spring, and acquire their full growth during the autumn, when a few undergo their metamorphosis; but in the larger number, this does not take place till the following spring, the tadpole period lasting about one year.

On the 8th of November, 1851, about thirty tadpoles con