lanthropic man, whose mind was ever meditating upon what might be useful to others, had the design of writing, when at leisure, a memoir on these subjects at large; but nothing of this kind appears to have been left behind him.

2. The second article selected for notice in the present supplement, is the Chevalier Aldini's publication respecting "the art of preserving from fire: [that is, as] applied to firemen and persons exposed to fire; with a series of experiments in Italy, Germany, and France." Prof. Griscom, having ably and clearly analyzed this work,* 1 shall select from his account of it, a few particulars belonging to my present subject; since they regard the security of those professionally employed in extinguishing the flames in burning buildings.

These particulars are as follows.-The bodies of persons exposed to the action of fire, are directed to be covered with dresses formed out of Amianthus, or with Sir Humphry Davy's metallic gauze ; and their hands also are to be protected by suitable gloves. The parties when they move among flaming materials, are likewise to carry before them, metallic gauze shields; and to be provided with pincers and other suitable implements, to perform such work as the case may require. They are moreover directed, when surrounded by flames, to keep themselves as much as may be in a state of motion; and are particularly cautioned not to remain long in a body of compact smoke.

The methods prescribed in the Chevalier Aldini's book, are not denied to be susceptible of farther improvement; but enough has been established to make the art, even in its present state, appear valuable as to practice. The experiments of several persons of high estimation, as Messrs. Gay-Lussac and D'Arcet, are among those cited to support its credit; besides the patronage of several governments, and besides other distinctions which were profitable as well as honorable.-One particular is added of moment, in favor of the plan, as regards expense; namely, that wool may be so prepared, as to become in "ordinary" cases, a substitute for amianthus in applying this art to use. In short, enough is said, to make it appear of consequence, not only to import into the U. States, the necessary dresses, &c. which belong to this art; but also to engage persons well acquainted with what belongs to this subject, to visit the U.

* See Vol. xx, No. 1, of this Journal, p. 96.

States, in order to communicate their knowledge to such persons here, as may be depended upon, to apply it to use when required. Whatever expense may be incurred in doing this, must fall short of the amount of the value put in Boston, upon a single picture, not yet exhibited, as well as of the sums actually paid or pledged for a single statue in several great cities of the U. States.

3. It is known that feather-beds, elastic cushions, and sometimes straw, notwithstanding its combustibility, have been placed in front of houses in flames, in order to receive persons who might venture to leap upon them from the upper apartments; but nothing of this kind seems in any degree so promising, as what has been called a stretched sheet; the invention of which is attributed to an EngJishman of the name of Wecks; the plan being stated to be as follows. A sheet is provided, in the borders of which large hoop-holes are left all round; in which holes, persons standing below (passengers and others) place their hands, in order to grasp the sheet firmly, and keep it extended. Hence, when the party leaping down from above strikes the sheet, the following results may naturally be expected. 1st. The holders of the sheet will drop it a little, in consequence of their slackening their hands, as soon as the weight of the descending person is felt. 2nd. The sheet is lowered farther, from the stretching given to the threads of which the sheet is composed. 3d. The sheet suffers a new depression, when the form of its surface, which at first resembles the cavity of the section of a hollow sphere turned with the open part upwards, is made to approach that of the horizontal section of the apex of a hollow cone also turned upwards. Each of these principles adding to the effect in diminishing the impulse of the descending weight, so as to make it gradual, the leap becomes harmless.-Accordingly, when an exhibition of the operation of this sheet was made in Southwark (which is considered as a part of London,) in the presence of numerous spectators; among whom were some officers of the London Police who may be said to have been there, professionally; various persons leaped upon the sheet, one after the other, from the elevated parts of a house; and all reached the ground without accident.

The statement of this exhibition has probably not reached the U. States upon any other than newspaper authority; but as the case is recent, it may easily be inquired into; and, in the mean time, it is open to new experiments in this country. If the matter be substan

tiated, we may then congratulate ourselves on the discovery of an apparatus so simple, cheap, portable, and easily preserved, that few towns possessed of a moderate population need be without one; and smaller collections of people ought to be instructed in the mode of providing themselves with an extempore substitute; which however will probably require some experiments before it can be fully relied upon.

4. In casting my eyes lately over the paper published by Lord Mahon, (now Earl Stanhope) on the subject of securing buildings from conflagration, the following passage struck me (if I may be pardoned the liberty of stating it) as containing an oversight. The passage is this, being correctly copied, including its italics: "In mest houses it is necessary only to secure the floors."-Perhaps by floors his lordship means only the upper boards on which we tread, in passing over a house; and if so, I have nothing more to remark ;-but if he designs to intimate that in most houses we may omit attention to the stairs, he differs from French architects and from Dr. Franklin. In any event, as his lordship in his paper tells us how to treat stairs and even partitions, so as to make them fire proof, we are at no loss how to proceed.

5. Whoever wishes to see the whole of Lord Stanhope's paper as given in the London Philosophical Transactions, will find it reprinted with very trifling variation in Dodsley's Annual Register for 1779; and consequently he will there learn how to carry his lordship's plans into execution; and he will also learn the cost of each part of the work (as prices stood in England in 1778).-Should his lordship incline to listen to the voice of some of the friends of humanity, he will leave behind him minutes of the theory by which he conducted his practice, as well as an account of some of his more important unrecorded experiments.

6. In the present supplement I may be allowed to confess, that I spoke too transiently in my letter of the probability of steeping timber in certain liquids; in order to render it difficult for slight flames to take hold of it. Our chemists and artists are however now ripe for making important discoveries on this subject. The same may be said as to the invention of modes for extinguishing flames when raging.— The offer of prizes for successful methods of accomplishing these two purposes may have the double effect of exciting the attention of skillful men to these matters; and of engaging the public to become sufficiently interested in them to think of applying what shall be brought into their view to actual practice.

7. In what follows in this article I speak with diffidence. I have merely hinted in my letter, that iron beams have been employed in houses, to prevent the progress of fires. I now add, what I recollect to have heard, that a building in England furnished with iron beams and having in it a number of stories, being in flames, the floors fell in together; and again, we have been told lately, of a conservatory for plants near London, surmounted by a dome framed with iron, which suddenly fell in, no fire having concern in the event. This has led me to suspect the operation of a new principle, in these cases, to which, perhaps, due attention has not yet been paid; namely, the expansibility of iron in consequence of an increase of its temperature; notwithstanding iron is the least susceptible of expansion of any of the common metals. In the case of the inflamed building having different stories, (as mentioned above); even if it were ascertained that its iron beams were placed, some horizontally and some perpendicularly, still it will be allowed to be possible that all of these beams were not heated alike, as being placed at different distances from the main body of the fire; and in this case, a want of symmetry in the expansion of the different beams may have led to a contrariety of action in different parts of some of the main supports of the building, in consequence of which the downfall in question occurred.

In confirmation of this hypothesis I relate what follows. 1. The celebrated Thomas Paine once had in his possession an iron bar of more than one hundred feet in length, which he placed in a horizontal position on rests, along the side of a brick wall; and fastening one end of it immoveably in the wall, he left the other end free to move itself; when he found the free end so much affected by the changes. of temperature in the air, that it served him as a sort of thermometer as to the temperature of the atmosphere. 2. An engineer in the service of the United States has lately proved by observation, that when a coping-stone of great length is used for covering the upper tier of masonry in a wall, it cannot at times be prevented from shrinking, so as to leave a chasm between itself and the next coping-stone, by which rain can have access to the walls.* 3. The frequent difference of opinion of men of science and artists as to the cause of the ex

* It should be observed here, that it has been said, that some stones are capable of imbibing a great quantity of water, with little alteration in their dimensions.

plosions of boilers in steam engines, seems a third ground for the conjecture, that these gentlemen have not in their examinations on such occasions, invariably comprehended all the principles which have had a bearing on the subject.*

* It is only in a note that I am entitled to speak of the tenacity of metals, as having some concern in the case of machinery, where heat is employed; there being nothing in my letter to call for the mention of it; but a note may be admitted in this place to shew that both tenacity and expansion in metals may, on these occasions, have a singular operation. The case will become more striking where two metals are employed; for the metals may differ from each other on these points, as also be operated upon in different proportions as to these points at different rates of temperature. Of all metallic substances mercury has the least tenacity and most expansion; but both iron and copper have peculiarities worth noticing in these respects; particularly where both metals are employed together in the same machinery.

What I have to state on this subject will be founded chiefly on different data collected from the able report made on the explosion which occurred to the boilers of the steam boat New England, at Essex in Connecticut, on Nov. 9, 1833; to which report are affixed the names of three truly scientific gentlemen in the vicinity; namely, Benjamin Silliman, W. C. Redfield and Denison Olmsted; and those also of an expert artist, Daniel Copeland and an experienced navigator by steam John F. Lawson.

1. Datum. Mr. Smeaton gives the expansion of iron as 151 ten thousandth parts of an inch at 180 degrees of Fahrenheits thermometer; and that of copper as 204 ten thousandth parts of an inch at the same temperature; and Mr. Smeaton says, that his results sufficiently agreed with what others had ascertained at the same period. See Hutton's Mathematical Dictionary, article expansion; and the Phil. Trans. Vol. xlviii.—The report above mentioned says (p. 20), that the experiments of Guyton Morveau, shew, that the tenacity of iron compared with copper is nearly as 540 to 302; or more than 80 per cent in favor of iron.-2. Datum. Copper is weakened by the action of heat at about 250°; and a copper boiler will bear a greater pressure when cold, than when heated. An iron boiler if heated not beyond 480°, will bear a greater pressure, than when cold, (p. 14.)—3. Datum. Melted copper at a white heat, will pass through a high column of water, and remain for some time ignited at the bottom of the vessel. According to the statement of Mr. Adam Hall, ten pounds of copper heated to such a degree of redness as to be merely visible in the dark, will convert a pound of water into steam; making more than 27 cubic feet at the common atmospheric pressure. It follows therefore, that copper flues as they have, on the whole, an extensive surface and great density, may produce an uncontrollable quantity of steam, even at a heat far below redness. (See, says the report p. 17, the valuable experiments of Prof. Walter Johnson, in the American Journal of Science.)-4. Datum. There were a few square feet of iron plate in the chimnies [that is to each chimney, there being two boilers to the engine;] to which [plates] the steam had access on one side; and there can be no doubt that these flues frequently became red hot. (p. 17 and aslo p. 5.)-5. Datum. The position of the safety valve on the steam pipe was 20 or more feet from the boilers. The diameter of the steam pipes which led from the boilers was about 10 inches. (p. 8.) -6. Datum. The copper varied in thickness in different parts. (p. 6.)—7. Datum. A heavy fall or crash, or a sudden cracking, preceded the first explosion, which was(by all but one person who heard it,) thought unusual. (See 9, 10, and 20;

*