grees of heat and moisture in the atmosphere are necessary to their production; high degrees of heat always increase the spread, and add to the inalignancy, of the disease; filth, and other qualities of the atmosphere less known, vary their types and exalt their grades; the constitution of the patient renders him more or less susceptible of particular diseases; the addition of a ferment (which is found wherever the disease exists) most certainly communicates and characterizes it; and lastly, under certain circumstances of purity and temperature of the atmosphere, it is found almost impossible to propagate those diseases, even by the aid of a ferment; and this observation applies, in some measure, even to small pox, measles, &c.

The sentiment, therefore, which you express, and so well illustrate, that the contagious diseases of your third class, although they may originate in circumstances of heat, moisture, and filth, and some other less evident qualities of the atmosphere, yet are unquestionably, and with more certainty, produced and propagated by the introduction of a ferment characterizing the type and grade of the disease, is, I believe, strictly and literally true; and upon this opinion only can a well-regulated police and quarantine laws be founded. The question you ask, why A after visiting B, ill of dysentery, plague, yellow fever, &c. is seized with the identical disease of B, when you consider the universality of the fact, is decisive as to the existence of a peculiar virus, or fomes sui generis, producing that particular form of disease; and the observation of Sydenham, that the prevailing epidemic swallows up all other diseases, confirms it; and I think you treat the non-contagionists with too much lenity, when you say they differ from us only in terms: far from it; they differ in fact, and most dangerously so; for, by denying the generation of a peculiar ferment in and about the bodies of the sick, and the propagation of contagion from patient to patient, they deny the utility, and are led to the neglect of some of the most important precautions against the introduction, importation, and propagation of such diseases.

Your first class of contagious diseases is strictly and clearly defined; they can be communicated by contact only: is not the materies morbi of these diseases always generated within the body; and whether it consists of animalculæ, or a chemical mixt, are they to be found anywhere else?

The fact that the diseases of the second class are communicable at every season of the year, during the heat of summer as well as during the severest cold of winter, in a pure as well as an impure atmosphere, forms the best distinction between this class and the third. But in as far as it is true that none of the second class can be suffered more than once in a lifetime, I am almost led to conclude, that in these, too, the materies morbi can be generated only in the bodies of the sick: the first origin of these diseases, and their occasional re-appearance in places where they had not been seen for years before, I confess forms a difficulty,

but I do not think a contradiction to this opinion; the materies morbi in these seems to be of a grosser nature, not so readily assuming a very elastic æriform state as that of the diseases of the third class; and hence the circle of contagion is much more restricted near the bodies of the sick.

Of the third class the fomes may certainly be, in some instances, in the first place generated in the atmosphere, and for that reason requires particular circumstances of heat, moisture, &c. but finding materials in the bodies of the sick to act upon, it readily assi milates a large portion to its own nature, which being very elastic and æriform, spreads to a wider extent, and contaminates the atmosphere, particularly a foul atmosphere, in which similar ingredients are found to a great extent.

Your's sincerely,

Dr. HOSACK.

SAMUEL BARD.

No. III.

A DETAILED NARRATIVE of the EARTHQUAKES which occurred on the 16th day of December, 1811, and agitated the parts of North America that lie between the Atlantic Ocean and Louisiana; and also a particular account of the other quakings of the earth occasionally felt from that time to the 23d and 30th of January, and the 7th and 16th of February, 1812, and subsequently to the 18th of December, 1813, and which shook the country from Detroit and the Lakes to New-Orleans and the Gulf of Mexico. Compiled chiefly at Washington, in the district of Columbia. By SAMUEL L. MITCHILL, Representative in Congress, &c.

[Read before the Society on the 14th of April, and the 12th of May, 1814.]

THE beautiful comet which travelled through the northern celestial hemisphere during 1811, had offered itself plainly to view until the approach of the following year. Its elements, as calculated by Nathaniel Bowditch, Esq. and his learned associates, have already been placed before the public eye.

The tremendous storm from the northeast, near the end of December, 1811, began to leeward, near Cape Hatteras, and swept the American coast to the banks of Newfoundland, doing great damage to navigation, and exhibiting some curious facts in the history of the atmosphere. The particulars of this furious and memorable tempest have been

collected by myself; and are in readiness to be offered to the society at the first convenient time.

My present intention is to read to you the information I have gathered on another occurrence of those portentous days. I mean the phenomena of the earthquakes, which terrified the country about the same period, and which continued a long time afterwards.

On the morning of Monday, the 16th December, 1811, several shocks of earthquakes were felt at the city of Washington. The first of these happened at three o'clock; and in some houses was considerable enough to shake the doors and windows, and wake persons from their sleep. There were successive tremors. Tassels of curtains were seen to move; and pitchers of washing-stands were heard to rattle upon their basins. The sound was very distinguishable, and was believed by many to pass from southwest to northeast. The alarm was so great in some families, that searches were made from room to room, to discover the robbers who were imagined to have broken into the houses.

A second shock, though lighter, was experienced about six o'clock; and a third about eight.

A gentleman standing in his chamber at his desk and writing, in the third story of a brick house, upon the Capitol Hill, suddenly perceived his body to be in motion, vibrating backward and forward, and producing dizziness. Not suspecting at the moment that the uncomfortable sensation was caused by an earthquake, he examined his desk to know whether it stood firm. Finding that it did, he dropped his pen; and turning his eyes upward, discerned that the looking-glass, and other things hanging near him, were in a similar motion.

Another person was near a table placed beneath a mirror. Feeling a giddiness come upon him, he seized the table for support. The general agitation of the chamber and house ceased in about a minute ; but the looking-glass, which was suspended in the usual manner, con

tinued to swing for some seconds longer. These observations, made by Messrs. Bigelow and Moseley, may serve as specimens of a multitude of phenomena of those kinds.

The atmosphere seemed to forebode some unusual occurrence. One of my most correct and respectable friends, declared in conversation, and stated to me in writing, that he made an observation of the sky about ten o'clock that night. It was quite calm. There was not a breath of wind stirring. The air was perfectly clear and free from clouds. Nevertheless, it was uncommonly dark, and the stars which appeared in every part through the gloom, were lurid and dim, and afforded little light.

In Richmond the signs of an earthquake were witnessed by many persons. At three o'clock on the same morning, (the 16th of December,) there were said to be three successive shocks; another about six; and a third about eight. Several people were impressed with a belief that thieves had entered their dwellings; and in one of the most elevated mansions, the bells were set a ringing in both the upper and lower rooms. The noise and concussion were supposed by some to proceed from east to west.

It was stated at Norfolk that two very distinct shocks were felt in that town and in Portsmouth; to wit, at three and eight o'clock in the morning of the 16th. Some clocks were reported to have stopped; the doors rattled; and articles hanging from the ceilings of shops and houses, swung to and fro, although a perfect calm prevailed.

At Raleigh (N. C.) several slight earthquakes were felt on the morning of the 16th December. The first happened between two and three o'clock, and was distinctly perceived by all who were awake at the time. Two others were reported to have occurred between that time and seven o'clock, but were not plainly observed, except by some members