boilers, and should disapprove of them, write him a blustering letter, in the hope that his answer may lessen the effect of his opinion on the minds of the jury. (N.B. This last direction is to be used with extreme caution; because his answer may be any thing but such as you wish, and he may insist on its being read to the jury.)

If another eminent engineer gives a clear and decided opinion against your boilers, listen to him with all the patience you can; you will naturally feel very glad when he has said his say, and will not be so foolish as to ask him any questions-you will have had quite enough of him without that.

Throughout the whole business, you will take every opportunity of declaring that your boilers are the very best boilers in the world; and that the more boilers that burst, and the more people they kill, the more you and the company they belong to will feel convinced of their safety. This will make a forcible impression on the jury in favour of your good sense and discretion.

But there is yet a last resource when all other hopes fail. If you can only bring forward some one who may be supposed to know something about the matter, but who, from illness, or being nearly scalded to death, or any other trifling cause, has been unable to appear before the jury until the last stage of the proceedings, you need not despair. You may sooth yourself with the hope, that what he will say, may obliterate from the memories of the jury and the public, the unanimous opinion of all the engineers in the world,—much less in such a paltry place as London.

But, if the jury persist in refusing to be persuaded to think as you wish,why, you will, of course, conclude, they are the most obstinate set of men that could be collected together; and you have nothing left for it, but to yield to your fate with the best grace you may. I am, Sir,

2nd August.

With due commiseration, Your obedient servant,

S. Y., an Engineer.

LONDON MECHANICS' INSTITUTIONCLASSIFICATION OF THE MEMBERS.

Sir,-Widely differing opinions, havbeen very frequently circulated as to the description of persons constituting the members of the London Mechanics' Institution, I beg to hand for insertion in your Magazine the following classified list, recently made out by a sub-committee specially appointed to conduct this investigation.

A similar analysis has been made upon previous occasions by individual members of the institution, but the present is the first official document of the kind that has been prepared. The constitution of some provincial Mechanics' Institutions having appeared in your previous volume, I trust that of the parent establishment will be received with some degree of interest.

Had the particular occupation of the members been more carefully inquired into, from the commencement of the institution, I am confident that the accompanying table would have shown more favourably for the mechanics; but I apprehend, as it now stands, it will bear examination, and is such as can hardly fail to prove satisfactory to all the advocates of general education. The high integrity of the members forming this subcommittee is a sufficient guarantee for the accuracy of their report, which is also to a certain extent corroborated by the results of previous investigations.

The report says, "Your sub-committee have been at much pains, to render their report as accurate as possible; in order to effect this, they have gone over the whole list of members three times, and the result of their investigation will be found in the following report:"

"Some little difficulty has been experienced in classifying the trades, but where several members were found belonging to different branches of one trade, they have all been included in that trade. Thus, for instance, all the various branches of watchmaking, have been included under that head; and the same course has been adopted with other businesses.

"In consequence of such a classification as the present not having been probably expected, all the members, on entering, have not been particularly required to describe their trade or profession. Hence it happens, that a considerable number have given

FLAT CHAMBER BOILERS-SIR JAMES Sir, Mr. Hancock states (page 278), that he has examined the wood-cut and description referred to, in No. 775 of your Magazine, of a patent boiler, and finds that the boiler (Sir James Anderson's) is composed of flat chambers, for which he obtained a patent in the year 1827; and he adds, that as he "has never granted a license to any person to use his said invention for steam-carriages, no person can have a legal right to adopt

it."

Now, Mr. Editor, this sounds very well; but I will, with your leave, endeavour to show, first, that Mr. Hancock has no patent which gives him a legal

ANDERSONS' AND MR. HANCOCK'S. right to attempt to restrain any person from adopting flat chambers for boilers; secondly, that he has no legal patented right to prevent any person adopting or arranging such flat or any other sort of chambers, in a vertical position, side by side, with spaces between for the caloric and smoke to pass through; and, thirdly, that he has no legal patented right to prevent any person strengthening such chambers in any way he may please, whether by having bolts or rivets through each particular chamber, or by having link-bolts externally round one or more chambers.

In 1824, a Mr. Smith, of London, patented a boiler, for evaporating fluids, composed of two narrow flat chambers, he having previously obtained a patent for a single flat chamber, each composed of thin metal, which were strengthened by having a number of bolts and nuts through the said narrow flat chambers, such bolts being placed about nine inches apart, over its whole surface* (I believe nine inches is mentioned in Mr. Hancock's specification). Again, in 1825, a Mr. J. C. C. Baddaly+ obtained a patent for a boiler for evaporating fluids, which boiler was to be composed of several flat narrow chambers, placed vertically side by side, with spaces or flues between them for the caloric and smoke to pass through, with fire and furnace underneath the chambers.

Mr. Hancock, therefore, whose patent is said to have been obtained in 1827, being two or three years later than the above, cannot legally claim either flat chambers, or the mode of arranging them side by side, with flues or spaces between them, or the mode of strengthening them by bolts, or the fire or furnace underneath,-all these principles being combined and claimed in the above two patents.

I am, Sir,

Your obedient servant, A SHAREHOLDER IN THE STEAMCARRIAGE COMPANY.

July 31, 1838.

* Smith's (Furnival and Smith's) flat boiler we are acquainted with; it is totally different from Mr. Hancock's. Smith divided his boiler into two flat horizontal chambers, both of which contained water, but the fire was only in contact with the lower chamber, the steam in the upper being generated by the heat of that in the lower. As the partition dividing the boiler into two chambers was of thin metal, cross-ties of iron were used to strengthen it, as well as the top and bottom of the boiler, somewhat in the manner patented by Mr. Russel, and described in our 22nd volume, p. 366.-ED. M. M.

† Will our Correspondent give us a more particular reference to this alleged existing patent of Mr. Baddaly's? We have examined the register of patents kept in our Patent Agency Office, (for the accuracy of which we think we can vouch,) and can find no such patent as "A Shareholder" mentions. Fearing the existence of a flaw in our list, we likewise caused search to be made at the Inrolment, Petty Bag, and Rolls Chapel offices, in which all specifications are enrolled, but no invention by any one of the name of Baddaly, or of any name at all similar to it, had been specified. We hope that this is an error on the part of our correspondent, and not a wilful attempt at deception, as we were at first inclined to think.-Ed. M. M.

REPORT AS TO THE SAFETY AND EFFICIENCY OF JOYCE'S PATENT HEATING APPARATUS: BY J. T. COOPER, ESQ., &c. AND WILLIAM THOMAS BRANDE, ESQ. F. R. S. PROFESSOR OF CHEMISTRY IN THE ROYAL INSTITUTION.

In compliance with your letter addressed to me on the 10th of March last, I have undertaken an investigation of Joyce's Heating Apparatus, in relation to its heating powers, the quantity of fuel consumed in a given time to produce in an appropriate room certain increase of heat, also the amount of contamination the air of the room sustains in a certain time, as likewise the deterioration of the air by the combustion of oil, tallow, spermaceti, stearine, and gas, with the view of estimating the comparative injurious effects of Joyce's stoves, and of other methods, by which heat as well as light are produced; and also of the amount of contamination the air undergoes, in places where a number of individuals are congregated, and in which no injurious effects are found to occur.

In the outset I may state, that the room in which the experiments have been conducted, is nearly 14 feet long, 13 feet wide, and 12 feet high, and, consequently, contains about 2000 cubic feet. It has a chimney, and a peculiarly accurately fitted and well constructed register stove, which, when shut, effectually closes its lower aperture. Whenever a particular trial was to be made, bags of sand were placed on the junctions of the window sashes, and also at the bottom of the doors, and every precaution taken to make it as air tight as could be.

I find that one of Joyce's stoves, the internal cylinder of which is six inches in diameter and fifteen inches high, with an inverted cone, having twelve holes, each a quarter of an inch in diameter, burns three, ounces of the prepared fuel per hour, when the regulating apertures at the top are quite open; in one instance, with a particular kind of fuel (such as is not commonly sold) it burnt three ounces and 4-10ths. ; but taking the average of a great number of trials carried on for days, its rate of burning is a fraction less than three ounces per hour; but in all cases the combustion proceeds without producing any of the unpleasant odour that occurs when charcoal of the ordinary kind is burnt in a similar manner.

In one instance, the stove was kindled, and at eleven o'clock in the evening was placed in the above-named room, the temperature of which was 62 degrees Fahr.; the room was then closed, and not entered till ten o'clock the following morning; I then remained in the room about an hour, the doors and windows being kept closed, and

found that exactly thirty-six ounces avoirdupoise of the fuel had been consumed ; and on testing the air taken from the upper, lower, and middle parts of the room, the greatest quantity of carbonic acid contained was three quarters per cent. The temper

ature had increased to 724 degrees Fahr.

In another experiment, the stove was allowed to burn fifteen hours in the closed apartment, and at the end of that time, it had consumed forty-four ounces and a half of fuel; and the air of the room on being tested for carbonic acid, as before, was found to contain less than one per cent, and the temperature had increased 13 degrees.

These experiments have been made repeatedly, and always with the same results, excepting some slight differences in the increase of heat.

It can be demonstrated as follows, that each ounce of pure charcoal, when burnt, will produce a little less than two cubic feet of carbonic acid: for, one hundred cubical inches of carbonic acid is estimated to weigh 47 grains, and every 22 grains of carbonic acid is known to contain 6 grains of carbon; then as 22 is to 6, so is 47 to 12.82, which is the weight of the carbon contained in 100 cubical inches of carbonic acid; then if 100 cubical inches of carbonic acid contain 12.82 of carbon, 1728 cubical inches, or one cubic foot, will contain 221.53 grains of carbon: again, if 221.53 grains of carbon be contained in one cubic foot of carbonic acid, one ounce avoirdupoise or 437-5 grains will be contained in 1.97 cubic feet, which is so nearly two cubic feet, that, for my present purpose, it may be said that one ounce of pure charcoal will produce two cubic feet of carbonic acid.

If no change in the air of the apartment had occurred in the two cases before related, there should have been present in the first instance 72, and in the latter 89 cubic feet of carbonic acid, which would have made the per centage 3.6, and 4.45; whereas, in both cases, it was less than one per cent, thereby showing, that whatever care may be bestowed to render a room air tight, that it is not possible to accomplish it so completely as to prevent the escape of the warm air, through minute pores and crevices from the upper parts of the room, and the entrance of the cooler air at the bottom, for in no other way am I able to account for the difference observed in the quantity of carbonic acid produced, and that detected in the air of the

room.

An imperial pint of good sperm oil will burn, in a well trimmed Argand's lamp of the ordinary size, about twelve hours; but I find by my analysis, that a pint of such oil contains 6333 grains of carbon, or nearly 14.5 ounces avoirdupoise, making the quan

tity of carbon consumed in one hour, a trifle more than 1.2 ounce; which, as I have shown above, is equivalent to the production of 2.4 cubic feet of carbonic acid. It will follow from this, that two such table lamps burning together will produce nearly as much carbonic acid in the same time, as one of Joyce's stoves, such as I have used in my experiments, and which I have before stated to be adapted for warming an apartment, containing about 2000 cubic feet of air.

A moulded tallow candle (long four) burns, on the average of some hours, 122 grains of tallow per hour; but in 122 grains of tallow there are about 95 grains of carbon, consequently, about fourteen such candles burning together, would produce as much carbonic acid in the same time as the Joyce's stove to which I have before alluded.

A spermaceti candle of the same size, will burn in one hour 129 grains of spermaceti ; but in 129 grains of spermaceti there are about 100 grains of carbon, consequently, about thirteen such candles burning together will produce in the same time as much carbonic acid as the Joyce's stove.

A stearine candle of the same size will burn in an hour 156 grains of that substance; but in 156 grains of stearine, there are about 121 grains of carbon, consequently, eleven of such candles burning together will produce as much carbonic acid in the same time, as the Joyce's stove.

Another stearine candle from a different maker with a larger wick, but of the same weight, (long four) will burn 175 grains in an hour; but in 175 grains of stearine there are about 136 grains of carbon, consequently, between nine and ten of such candles burning together, will produce as much carbonic acid in the same time, as the Joyce's stove.

Coal gas of average quality, I have found to produce by burning, 0'6 of its bulk of carbonic acid; an ordinary coal gas burner on the Argand's principle, having fifteen holes, will consume 5 cubic feet of gas per hour; six tenths of five are three, therefore, three cubic feet of carbonic acid would result from one such light, consequently, two such gas lights burning together, will produce exactly the same quantity of carbonic acid as the Joyce's stove.

But, independently of the formation of carbonic acid, all the common combustibles last named, contain such excess of hydrogen as tends to the further deterioration of the air, by the abstraction of an additional portion of its oxygen, so as to leave an excess of residuary nitrogen, which, of itself, is nearly as deleterious as carbonic acid; the air, therefore, which issues from the glasses of Argand, oil, or glas lamps, or from the flames of candles, will, if received into a

proper vessel, by which the entire products of combustion may be collected, prove equally, if not more, deleterious to animal life, than that which results from the combustion of an equivalent quantity of charcoal.

With a view to determine the amount of deterioration the air underwent in crowded assemblies, I obtained some air from a chapel in my neighbourhood, towards the close of the evening service, and, on examination in the ordinary way, it was found to contain a little more than one and a half per cent. of carbonic acid. In another instance, I collected some air from the gallery of a crowded theatre, at eleven o'clock in the evening, about four hours after the commencement of the performances, and this I have found to contain about three per cent. of carbonic acid.

The advantage which I conceive Joyce's stove to possess over the ordinary methods of burning charcoal for warming apartments, is the perfect control over the rate of combustion of the fuel; for while, in a common chafing dish or brasier, almost an unlimited quantity of charcoal may be consumed in a comparatively short space of time, and liberate very suddenly a large volume of carbonic acid, which might be prejudicial to health, if not absolutely dangerous; in these stoves, by their peculiar construction, and arrangement of proper-sized apertures, the fuel can be consumed only at a certain given rate; and, if they be properly adjusted to the size of the apartment they are intended to heat, my experience leads me to believe, that no injurious consequences can arise from their employment.

JOHN T. COOPER.

82, Blackfriars Road, London,

June 14th, 1838.

Having been present at the experiments made at Mr. Cooper's house, with a view of determining the degree of deterioration which the air suffers by the employment of Joyce's stoves in close rooms, and having examined, in conjunction with him, the composition of the atmosphere under such circumstances, I can certify, that after burning for twelve hours, in a close room of the dimensions above stated, that less than one per cent. of carbonic acid was, in all cases, found in the air of the room; that such proportion of carbonic acid cannot be considered as deleterious, or in the least degree dangerous, in reference to respiration; that it falls short of the relative quantity of carbonic acid found in crowded and illuminated rooms, or in buildings in which many persons are congregated, such as churches, theatres, and assembly rooms, in which ventilation is generally imperfect, and in which, as far as my experience goes, the relative proportion of carbonic acid always considerably exceeds

one per cent. I am, therefore, of opinion, that the said stoves, which are so construct→ ed as to consume only a limited quantity of pure charcoal in a given time, may be employed with perfect security, for all the purposes for which they have been proposed, and I consider the grounds of this opinion sufficiently detailed by the experiments above given.

WILLIAM T. Brande.

London, June 14, 1838. To Mr. William Harper.

Note on Mr. Cooper's Letter to Mr. Harper, respecting Joyce's Stove.

(From Sturgeon's Annals of Electricity.)

Having made a very careful perusal of Mr. Cooper's letter to Mr. Harper, on "Joyce's Stove," we are prepared to furnish our readers with some additional information respecting the use of that apparatus. We shall premise by observing, that the first impression which the reading of Mr. Cooper's letter left on our mind was this: that, sanctioned as it is by Professor Brande, it is much better caleulated to be serviceable to the venders of Joyce's stoves than to the purchasers of them; for it is sufficiently obvious, even at first sight, to a scientific man, that Mr. Cooper's experiments are not only deficient in point of number, but appear to us, whether selected or not, to be eminently calculated to convey to the unwary, an exceedingly partial view of the real value of the apparatus.

It might seem necessary to inquire, why Mr. Cooper's experiments were made in a natural atmosphere which required no artificial heat to make it agreeable? Are the purchasers of these celebrated stoves to understand that they are to be used only at those times when the natural temperature of the room is 62° Fahr.? Is this the information they receive at the sale rooms? If, on the contrary, Joyce's stove be intended to be more generally useful, and to compete with other modes of warming apartments, we readily perceive that Mr. Cooper's experiments would have afforded a much more perfect view of the real value of the stove: and, consequently, would have been of far more importance to the public, had they been made at those natural temperatures of the atmosphere in which artificial heat is generally wanted.

If proper experiments had been made during the severe weather of last winter, and that no other artificial source of heat than that produced by the combustion of three ounces of charcoal per hour had been in the room, Mr. Cooper knows very well, that the results would have been very different to those stated in his letter.