suburbs has been wholly unattended by any public fire-engine or fireman, and but for the exertions of the servants of the Insurance-Companies, whole streets would have been swept away in one common conflagration as of yore.

P. R. repeats a question to which he might as well take an answer from my last letter. If he is really a friend of Mr. Braithwaite's, and wishes well to his invention, he will cease to press the matter so pertinaciously. It is not for P. R., nor myself, to dictate the employment of such a machine; doubtless the parties to whom we think it would prove useless, will avail themselves of its aid so soon as they are satisfied of its economy, superiority, and trustworthiness. I remain, Sir,

Yours respectfully,
WM. BADDELEY.

London, Dec. 27, 1836.

THE INSURANCE SYSTEM.

Sir, Your correspondent, "Fire-Fury" (p. 227), if he had had his eyes about him, might have found a much more indigestible fact for Mr. Baddeley's mastication than that he has brought all the way from Manchester-and without going so far from home in search of it. Ia the very Number of the Mechanics' Magazine which was graced by his former letter (No. 696, p. 182) will be found a piece of evidence which throws much more light on the principles and practice of the Fire-Insurance Companies than a thousand such facts as those adduced by our friend with the terrific signature. I allude to the evidence of Mr. Walker, the eminent engineer, before the House of Lords' Committee on the danger from fire in the use of locomotive-engines in narrow streets. He tells us, that when employed as engineer to certain extensive water-works, one of whose objects was the better prevention of damage from fire, he waited on one or two of the Insurance-Companies, with the expectation that they would take particular interest in the matter, and he goes on to observe, "I was surprised to find the great indifference they had towards it, and I inquired how it was, and I remember one of the officers told me, the truth was that they gave themselves little concern about it, because it did not injure them; I said, How does it not injure you, have not

you to pay the losses?' His reply was, that if they had not fires occasionally, they should have no insurances."

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Now, this broadly-stated fact certainly appears to be by no means corroborative of Mr. Baddeley's very decided opinion, that " every nerve has been strained" by the Insurance-Companies" to render the Fire-engine Establishment as effective as possible" and to tally as little with his answers from his own personal knowledge" of "YES" to Fire-Fury's question, "Whether the Companies desire a more effective instrument than the engine now in use?" In point of fact, this nerve. straining" appears to be a very inconsistent piece of business, even on the view of the state of the case put forth by Mr. Baddeley himself, which is doubtless the correct one. How can it be expected that the Companies should "strain every nerve" to increase the means of protecting property, two-thirds of which (the uninsured proportion) belongs to parties who pay them nothing, whether it is burnt or not?

The matter seems plain and straightforward enough; and Mr. Baddeley and his adversaries are perhaps not so widely at variance as they imagine themselves to be. "The Insurance-Companies do not patronise the most effectual means of extinguishing fires," cry P. R. and FireFury. Mr. Baddeley rejoins, indeed, that they do; but at the same time takes care to show the reason why they do not, and why it cannot be expected that they should do it; while Mr. Walker's evidence steps in by way of "clincher." It is quite obvious, that if preventive and other measures were carried to such a point of excellence that fires seldom occurred, and when they did occur were speedily put out, the inducement to insure would be very small. Now, this is the precise point at which it is the interest of the public to arrive; but can it be, for a moment, contended that it is also the interest of the Insurance-Companies? If the London Establishment were to adopt Mr. Braithwaite's steamer to-morrow, and it proved such a complete fire-eater as its advocates assert it to be, so that the moment a conflagration was discovered, it steamed i.self off to the point of action, and forthwith destroyed every vestige of "the devouring element," what would be the natural effect? Why, that no new insurers would come

in, and most of the old insurers would back out! "A consummation devoutly to be wished," indeed, on the part of the Companies who had expended their thousands in encouraging invention whose success must needs involve their ruin!

This makes it clear that the matter really stands as P. R., in his original communication, supposed it to stand-to wit, "the Insurance-Companies v. the Public Security," inasmuch as if the public security were perfect, InsuranceCompanies would cease to exist. Mr. Baddeley admitted as much in his reply, contending, very reasonably, that it was absurd to call on the Insurance-Companies to protect the whole of the property of the public," when they were only paid for protecting, or rather for guaranteeing the restoration of one-third of its amount. Yet, with some degree of inconsistency, in his last letter he vouches for the desire of the Companies to procure the most effective means, and to "strain every nerve" to perfect the system of wholesale protection. How is

-this ?

Fire-Fury and Co. deal very largely in threats of "public reprobation." But where is it to fall? On the InsuranceCompanies? No; they conduct their "trade" in the way best calculated to bring in the most profit; i. e. they like a fire now and then, provided it does not burn too large a quantity of insured property, and make a great parade with firemen in melodramatic costume and most imposing helmets, while they throw cold water on any new scheme for putting out fires too fast, and with too little stage effect! It is "the public" that ought to meet with "public reprobation." It is to "the public" interest that the property of "the public" should be preserved; and if "the public" neglect to take the proper means of doing so, in the name of common sense, let "the public" bear all the obloquy.

Before I conclude, let me say a word on the analogous subject of "Marine Insurance." A Committee of the House of Commons, it appears, have promulged it as their opinion, that the system of ship-insuring is pernicious, because “the risk of loss can be covered by a fixed premium of insurance, which being charged on the freight, and re-charged on the goods conveyed, fixes the real loss and real responsibility ultimately on the pub

lic." What a discovery to be set forth in these politico-economical days! Do the Committee really mean to assert, that the price of goods is determined by the mer. chant, and that "the public" (poor soul!) puts his hand in his pocket, and pays whatever he chooses to demand? Do they actually think that the merchant and the ship-owner may settle what the amount of freight" shall be betwixt them, and that the much-enduring "public" is forced to reimburse the merchant, whether he may choose to give one pound per ton or one thousand? If not, where is the point of their observation ?

Whether the merchant imports his commodities in insured or uninsured ships, the price paid him by "the public" is the same; it is, therefore, his interest to reduce all the charges as much as possible, and he will hardly go to the expense of insurance if that expense is not required. Custom, indeed, may do a good deal, but it is too much to suppose that it should induce a merchant to pay a shipowner an increased freight, in order that the ship-owner may pay a large sum for insurance to the underwriters; when all the while he might employ a vessel which would be certain to perform the voyage in safety, without any need of troubling the underwriting fraternity at all. But then, say the Committee, it is nothing to him; he charges it all on the public! If so, why not send a sound ship, and put the insurance-money into his own pocket? I remain, Sir,

Your most obedient servant,
AQUARIUS.

Dec. 28, 1836.

AERIAL NAVIGATION-A SUGGESTION.

Sir,-The late bold aerial voyage of Messrs. Green, Holland, and Mason, will, in all probability, lead to attempts of still greater magnitude. From the suggestions of many, some improvements may ensue, which may perhaps facilitate the next great attempt. With much diffidence, I presume, through your journal, to suggest the following plan, which would, under some circumstances, enable the aeronauts after descending to re-ascend and continue their route.

The ballast should in part consist of well-made recipients filled with condensed gas; to each recipient a wellmade stop-cock should be attached, and which should be fitted to a cock connected

by an elastic tube to the balloon. By that method the gas discharged in the descent might, in some measure, be replenished. To recondense gas into the recipients from the balloon, would be more difficult, but not impossible; and I think a light and simple apparatus for that purpose might be constructed.* Could this be effected, the deserts of Africa might be crossed, as the winds are during certain seasons not variable. A country like Australia might be surveyed, and even the belt of the trade winds made a highway. To try the latter, a vessel might carry gas recipients charged with condensed gas, and the balloon might proceed to a certain latitude where, either over the launch or on a raft prepared, the balloon might be inflated from the recipients as readily as in Vauxhall Gardens, and then left to the winds and the management of the aeronauts. The best gas-recipients I ever saw were made by a Mr. Bowser, not far from St. Katharine's Docks; as some time has elapsed since I saw them, there may be others lighter and sufficiently strong for the purpose. There is no difficulty in constructing tubes six inches diameter and three feet six in length, which weigh only nine pounds, and which I constantly use at three hundred pounds pressure of steam on the square inch, and which are quite safe at 1000.. It would be premature to enter farther on this subject. If it is worthy of the aeronauts' attention, I can always be communicated with; and I will merely add, that it would give me pleasure to put the idea into practice.

Your obedient servant,
NATHANIEL OGLE

Albion Club, St. James's-street,
Dec. 26, 1836.

ON CASTING AND GRINDING SPECULA.

(Continued from p. 219.)

Sir, Referring to my last letter, I now proceed to describe the process of modelling the metal in the sand. The boxes or flasks should be similar to those used by brass-founders, excepting that the upper box should be deeper than the lower, as the former contains the metal and block. Fig. 1 represents a section of the boxes when ready for pouring;

This has been repeatedly proposed; but I be lieve never tried.

a, the metal; b, a large block of wood in the shape of a cone with its vertex removed, and also a small piece cut off one side by a perpendicular section. The use of the block b is to afford a reservoir or supply for the metal which contracts on becoming solid; and as the block from its size is always fluid some little time after the casting itself ceases to be so, it affords a supply to the latter and prevents its cracking or sinking on the back. So completely does it answer this purpose, that on removing it from the sand it is scarcely more than a shell; its section being similar to that marked out by the dotted line b. For this essential improvement in the art of casting, as, indeed, for many others connected with the subject, I am indebted to my friend Mr. Carnfield, late of Northampton. It is in vain to try to cast metals with only a small git, as they will invariably be found cracked when the boxes are opened. A piece of wood is to be modelled in the lower box, the size and shape of which will be understood by the two views of it given at c, figs. 1 and 3; d, fig. 2, represents the lower end of the git; e, fig. 3, a little well or indenture made in

the lower box to receive the first splash of metal in pouring; f, the channel or course for the metal from the git to the block, whence it flows into the mould for the mirror itself. The process of modelling is this: the patterns a and b are laid on a smooth board (the dimen sions of which are something greater than those of the boxes,) in the situation shown in fig. 1, the flat side of the block next the mirror not touching it, and yet not more than one quarter of an inch from it. A piece of wood of the form g, fig. 1, should also be placed upright on the board, as in the figure, at least some inches distant from the block. Its length should be exactly equal to the depth of the upper box-this is for the git or pouring hole. The box is then to be filled with damp sand, such as the brassfounders use, and moderately rammed, sufficiently so to make it firm, but not too hard. The surface must be very even, and just the height of the edge of the box. A board similar to that under the box is now to be laid on the top, and the whole inverted. That board which is now uppermost is to be removed, and some dry ashes scattered through a fine sieve over the surface of the sand, keeping them as much as possible off the face of the pattern. Place the little pattern c exactly on the block, which will be more readily done if it have two pins standing out to fit corresponding holes in the block. This box is to be rammed exactly as the other; and when a board has been placed on the top, it is to be lifted off the first box, and set aside in an inverted state. With a little water moisten the edges of the sand round the patterns, and then carefully draw the block pattern with a gimblet; cut away a part of the small bit of sand between this and the metal, making the opening very little more than half the thickness of the metal; two-thirds the thickness may, however, be cut away with safety. Attention should be paid in ramming the first box to have the sand between the mirror and block pretty firm. Draw now the mirror pattern in the same way, and with a strong knitting-needle, make a few air-holes in the sand, which is above the top of the block, but make none elsewhere. The small pattern for the lower part of the block is now to be drawn from the lower box, and with a small modelling trowel, cut the course ƒ in the

sand, making the well e just under where the pouring hole will be. It may here be remarked, that instead of having to cut the channel and well, it will be better to have wooden patterns for them, by which method they will be formed more neatly, and with less trouble and danger. They are, if used, to be modelled in the lower box along with the pattern c. A little flour may be dusted over both sand surfaces, which will cause the metal to quit the sand more easily. The boxes are to be set on edge, and gently blown with a pair of bellows, to take away any loose grains of sand, and then carefully put together. A pair of wooden screws must be employed just to keep the sand in the upper box from rising by the column of metal; and some care is necessary, in order to restrain the sand from lifting without exerting any pressure downwards. The metal in the crucible should be stirred after taking from the furnace, and well skimmed, which should be done as quickly as convenient, that it may not get cool. It is difficult to give a correct idea of the proper degree of heat of the metal; it should be sufficient to render it perfectly fluid until the mould is just full, and any greater heat than this is hurtful, The boxes are to remain undisturbed after pouring until the top of the gig is become almost black, when a thin rod of iron may be put through the thin stratum of sand, which is over the block, to feel if it is become solid; if it is, it is then quite time to separate the boxes. The sand should be in part cut away, or carefully loosened from about the git and block, in order that the upper box may be lifted off without any danger of disturbing, and thereby warping the metal in its hot state. The mirror should be dull red when first exposed. At that part of the channel, which is about an inch from the block, lay a piece of rag soaked in cold water, which will cause it to break across, and thus separate it from the metal and block.

Previous to this period of the process, preparation must have been made for annealing the metal, which is absolutely essential to its safety; but as my letter is already sufficiently long, I shall leave the subject for my next,

WM. LASSELL, Jun. 18, Norton-street, Liverpool, Dec. 17, 1836.

That to effect this general adoption is no such easy matter as your correspondent appears to think is, in my opinion, clearly proved by the history of the French system of weights and ineasures, expressly contrived by a leading Society" in France, for the general use of civilised nations; but which is so little known or thought of here, that your correspondent, though writing on a subject so closely connected, appears never to have heard of it. The invitation given by the French mathematicians appointed by the Institute to those of other nations to concur with them in establishing a scientific system of measurement, was not accepted; perhaps with some reason, for the French capital was not at that time the safest residence in the world for scientific characters, and the framers of the new system were so entirely scientific, that they contemplated a decimal division for every thing whatever, and could not allow even the seventh day to remain holy. This inclination, and their intention of dividing time and the geometrical circle into decimal parts, led them to select for the metre, or standard of linear measure, the ten-millionth part of the quarter of the circumference of the globe; a choice which that a proves leading learned Society" will not always pursue the line of conduct dictated by common sense. The circumference of the globe

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cannot be considered as yet so accurately determined as to render it advisable to take it for a scale of measurement, nor is it probable that it ever will be; and the proportion of the new measure to the old ones, which was an object that ought not to have been lost sight of, was most unpleasantly fractional-one metre equal to 3.079458 Paris feet. In fact, almost the only recommendation of the new scheme was its connexion with a decimal system of augmentation and subdivision. Ten metres, according to the table, made 1 decametre, 10 decametres 1 hectometre, 10 of the latter one kilometre, and 10 of those 1 myriametre, or 10,000 metres; while, on the descending scale, one-tenth of a metre was a decimetre, one-tenth of that a centimetre, and one-tenth of that a millimetre. Latin names were thus adopted for the descending, and Greek (bad Greek, by-the-bye) for the ascending scale; while, as Latin is more generally understood than the other language, and the ascending scale more frequently used than the descending, the reverse might have been considered more advisable if it were thought proper to compound the names from two languages at all; and even by that cumbrous means the risk of confusion is not avoided, as the words decimetre and decametre bear certainly too close a resemblance. However, in spite of all these objections, the new measure was adopted, and adopted with vigour too. A model of it in platina, as the most unchangeable metal, was constructed and deposited at the French Institute; others in metal, with marble casings, were built into the walls of the principal public buildings; on the great high-roads stones were erected at the distance of every kilometre; in short, every method was taken to bring it into use, and yet what has been the result? In France itself distances are still reckoned in the old French foot; in England it is not easy to point out any work, except a Universal Cambist, which contains any information as to what the French weights and measures are, and in the recent alterations of our standards no attention has been paid to them.

Since there thus appears to be an insuperable vis inertia, or power of lazi ness, in existence to oppose the introduc tion of a standard merely brought for