the pressure, and inversely as the diameter of the wheels.

2. The wear of the road is greater in proportion as the wheels are smaller. 3. On roads of compressible materials, as earth, sand, gravel, &c., the wear and the resistance to rolling decrease in proportion as the breadth of the wheeltires is increased, and with all carriages is independent of the velocity. 4. On paved roads, or ordinary stoned roads, (en empierrement,) the resistance is nearly independent of the breadth of the tire, within certain limits, and increases with, and is proportional to, the velocity. The augmentation is less as the carriage is better hung (i. e. on springs) and the road more firm. At slow speeds, the resistance is the same for springed and unspringed carriages.

These are results of M. Morin's first memoir, some of which, it may be observed, do not agree with those admitted amongst British engineers. The second memoir contains his results as to the relation between the form of wheel and wear on the road. The mode of experiment adopted was that proposed by M. Navier, viz., the causing the same load to pass repeatedly over the same track of road, and observing the depression. This method was proposed by Navier in an able work published by him in 1835, and little known to Englishmen, entitled "Considerations on the Principles of the Police of Wheel Carriages."

M. Morin's principal results in this Report are

1. With equal loads, narrow tires degrade roads more than wide ones; but with loads of 5,500 kilograms, and tires of 0-12 metres wide, the advantage of width is a maximum, and beyond this there seems to be no use in augmenting the width.

2. Another set of experiments indicate that, with loads proportional to the width of the tires, the widest tires injure the road most.

3. With equal loads and widths of tire, greatest injury results from the smallest wheel.

4. The same load carried in two twowheeled carts produces less injury than in one four-wheeled wagon. 5. A springed wagon, at a trot pace, produces as little injury as an unspringed one at a walking pace. The

201

Water-proof Cloth.

M. Menotti's invention of a soap in solution, for the purpose of rendering cloths water-proof without stopping their pores to air, &c., was reported on favourably by a commission of the Academy, in January, 1840, and the subject has been again brought by him before this body. This invention of Menotti's is nearly, if not quite identical with that patented by Raper in this country, and both are alike useless. It is quite true that either of these plans, (if they differ,) or any one of many others of long anterior date, will enable cloth to resist water gently poured over it, but a very little rubbing or sopping of the cloth sends it through the fabric; so that, although a coat might bear a shower, say on the shoulders, it would wet through under the arms, &c., in a short time.

The principle of all the methods consists in fixing in the pores of the cloth either an oily matter, by decomposition of a soap, or an extremely divided powder, having little or no affinity for moisture. As yet, no water-proof cloth exists but that made so by India-rubber, or at least, none that will remain so.

Manna.

A substance has recently been introduced into commerce as manna, in France, but which does not possess all the properties for which that drug is valued. It is questionable whether the new substance is an artificial or natural product; and it has been examined chemically by Pelouze, and optically by M. Biot, by means of polarized light, according to his own peculiar method.

Mannite, the peculiar proximate principle to which manna (which is a secretion from certain trees of the genus Fraxinus) owes its efficacy, has scarcely any estatory power on the polarized ray. The

solution of manna, however, like that of dextrine, or starch modified by the action of acids, causes the ray to deviate to the right of the observer, which arises from its containing a quantity of fermentable sugar. This renders the optical examination of this new sort of manna not quite decisive, as its effects on light are similar. This substance consists nearly wholly of fermentable sugar, very analogous to that produced by the action of acids on starch; and although it cannot be pronounced certain, it seems not improbable that this new sort of manna is, in fact, so made.

Causes of Explosion in Steam-boilers.

The formation of explosive mixtures of gas by decomposition of water in iron boilers, when in contact with red-hot plates, has been repeatedly urged as a cause of explosion; and as repeatedly has it been shown that, although possibly hydrogen might be thus produced, an explosive mixture could not, as the oxygen is not set free, but taken up by the iron while it oxidizes. M. Jobard, Director of the Museum of Manufactures at Brussels, has published a paper, in which he reasserts this to be a true cause of explosion, and gets over the difficulty as to oxygen by saying that atmospheric air takes its place; that, in fact, water cannot be decomposed unless the water be low in the boiler, which cannot happen unless the feed-pump be out of order, that is, not pumping water, but pumping air into the boiler.

He explains, then, the ignition of the inflammable compound to arise either from the contact of the red-hot plates, or from an electric spark produced by opening the safety-valve, and the steam rushing out.

It is now well known that a discharge of steam is accompanied with a powerful disturbance of electrical equilibrium; but it is not so evident how this is to produce a spark, in such circumstances as to ignite the supposed issuing volume of gases.

It requires a bar of iron to be nearly white-hot, before it will ignite an explosive mixture of gases. A more likely source for the air would be, apparently, that it is introduced into the boiler in combination with the feed-water, and there evolved on its being heated.

Some curious examples of explosion are cited by M. Jobard; among others, one of a boiler at Ghent, which was blown up while the man-lid was off, and the boiler about to be cleaned out. On the whole, as there is no doubt whatever that iron, aided by high pressure, (as, for instance, Perkins's Hot Water Apparatus,) will decompose water at temperatures even below ignition, it is quite possible that some explosions of boilers may have been due to this peculiar, but certainly most unlikely, combination of circumstances; while there can be equally little doubt that the vast majority have arisen from simple pressure of surcharged steam, a cause, however, which, M. Jobard will not admit under any circumstances; for he says, a boiler gradually overpowered by steam pressure rends at the joints, which first open, and give vent to water and steam. A complete treatise upon the causes of boiler explosions is yet a desideratum every author hitherto has had some favourite crotchet to support, besides the main point of the matter.

The Artesian Well of Grenelle.

In a letter to M. Arago, Mr. Combes gives his opinion as to the causes of the singular flattening of the copper tube lately put down into the bore by M. Mulot, and which has caused so much trouble to get up again. It is pretty generally known already, that, after more than 600 feet of the copper tube intended to line the well had been got down, without any accident, suddenly, in one night, above 300 feet in length of the tube became compressed together flat, and twisted in various directions, grasping and retaining a spoon which had been before lowered down into it. The following is the theory of the phenomenon given by Mr. C. The inside of the jumper-hole had been previously lined with sheet-iron, at intervals, to support its sides. The water of the upper chalk continued to discharge large volumes of sand, which are supposed to have filled up and got wedged between the two tubes, and so stopped up all egress to the water in that way. As long as the water stood at the same level

inside and outside the tube, the pressures would balance each other, and no injury could result; but the water from the bottom of the chalk would carry up great quantities of solid matter also, and be subject to frequent stoppages, obviously caused by breakings-down, or wedging of particles in motion in its subterranean ducts. Mr. C. supposes, then, that the flow of water in the inner tube was arrested; that the level of the water in it fell, temporarily, much below that due to the pressure on the outside of the tube; that the water of the upper chalk was then corked up between the tube and the sides of the well; and that at this moment the sides of the copper tube were crushed inwards.

The portion of the tube crushed was from about 300 feet from the surface to about 600 feet lower.

New Application of the Electrotype.

M. Peyré, of Versailles, has proposed an application of the electrotype process which seems likely to be of value, viz., to the multiplication of accurate graduated instruments. It is obvious that, if one perfect graduated scale of metal can be had, without injury, we may electrotype others on it, and others off them, ad infinitum. The costliness and rarity of good graduation is well known to those who are at all concerned with instruments of precision. As a proof of the power of the process, very ample details of which M. Peyré gives, he states that a Daguerreotype plate, having a faint image of the Christ of Michael Angelo, gave him copies in copper, in which the design was as apparent as in the original.

MR. WILLIAMS'S SMOKELESS FURNACE

REPLY TO MR. ARMSTRONG.

Sir,-As Mr. Armstrong continues to repeat his unwarrantable statements, I must beg permission to make a short reply. He now attempts to neutralize the effect of his admission that his report was "founded on erroneous data." The only answer I shall make is, that I have the fullest confidence in the statements made by the solicitor, a wholly disinterested party. It is quite true, the letter of recantation was not written by Mr. A. himself. I never said it was: and your explanation, in the note attached to Mr. A.'s letter, renders any further observation on this point unnecessary. My assertion was,

203

that he had no grounds for stating that his conviction of the supposed injurious effects of my mode of admitting air to a furnace was, "forced upon him by a careful and unprejudiced examination of several furnaces constructed by Mr. Williams himself." His now triumphant answer is, that indeed he had seen one which was erected by the late firm of Brocklehurst and Company, and which, after a hasty examination, he ridiculed as a mere 66 'peep-show affair," (see Mec Mag, April 17). Now, this statement alone, so different in substance from his "long attention, and careful examination of several"-is a sufficient refutation. But as to this one furnace to which he refers, I have to state,-1st. it was not constructed by me, and in several respects differed from my instructions; 2nd, it nevertheless was successful in its operations; and 3rd, it never caused any injury-its internal action completely negatived the expanding and contracting, heating and cooling processand it ever continued to work satisfactorily. Thus, if the report was in any way influenced by the action of that furnace, it should have been the reverse of what it was. The object, however, was to throw discredit, in the garb of a matterof-fact report, on my principle of admitting air to furnaces. I am sorry here to have it to say, this is no solitary instance of a prejudging determination to condemn, without enquiry, and on the part of those whose real interests would suggest the most rigid impartial examination. But the main allegation in Mr. A.'s letter is, that I threw the responsibility of the action of my furnace, in the case of Messrs. Hamnett's boiler, on my agents. This,

Sir, is the very reverse of the fact; for, as it was important to me to disprove Mr. A.'s statement, that my plan of admitting air was, and "ever would continue" to be injurious, I adopted the most decided measures on that head. I wrote several times to Mr. J. Woodiwiss (the acting partner) on this subject: and the following extracts from my letters will set this matter right:

My letter of the 15th of December last, states, "I will, at my own expense, put the furnace in operation for any given number of days, which may be deemed advisable for testing the value of my system, and of proving to your entire satisfaction, that it is absolutely impossible

66

to injure a boiler by any operation of my system, so long as it is preserved in a proper state of cleanliness and with a due supply of water. The only condition I shall require is, that a water gauge be placed on the boiler, and by which the fireman can ascertain whether there is a sufficiency of water in it: and further, that until you are satisfied as to the safe working of the plan, I be allowed to have a confidential person to prevent any neglect," (I might have said-or foul play,) as touching the supply of water. I will give you any guarantee as to the safety of the boiler." This, I think, will be admitted to be the experimentum crucis: for, had I failed, and had Mr. A.'s theory been correct, the question Iwould have been at once and for ever settled, and to my discomfiture. Mr. Woodiwiss should at once have accepted the proposal, and Mr. Armstrong have advised it, as the best test to which his theory could have been subjected, and the surest annihilation of mine, if erroneous. But this offer, to take on myself the risk and responsibility, was declined, and uncourteously so. This was at least suspicious.

In my letter of the 27th of December, I said "I repeat my proposal to reopen the air-pipe, and show you that no possible injury could be sustained by the admission of air, as alleged by Mr. A." Again-" I undertake to make this application without auy expense to youwithout any charge for patent right, and with a guarantee against any, and all injury, from such admission of air." I trust, Sir, this will be a sufficient answer to the allegation that I threw the responsibility on others. Suspecting, however, that there was some understanding between the parties, I brought this to the test, by adding, "If you refuse me, the world will say you have consented to the erroneous statement, and are, in fact, supporting Mr. Armstrong in his unjustifiable attempt to injure me." My last letter to Mr. Woodiwiss states that his refusal was perfectly satisfactory, and the public would know how to appreciate it. Mr. A. states, that I was present, and a "witness of its failure." I was present, and, on the contrary, witnessed its success. The alteration was one suggested by Mr. W. himself, namely, the stopping the action of Stanley's feeding apparatus, and which I

at once had objected to, as defeating my principle; seeing, that by the action of Stanley's feeders, too thin a fire is maintained on the bars, and so large a quantity of air is drawn in from the front as effectually to obstruct the action of the air introduced in the proper place from behind.

Mr. A., very naively observes, that his statements have been "verified to the satisfaction of every one who has chosen to enquire of the proprietors of the boiler in question." No doubt of it. But what say those who have enquired of other, and disinterested, and unprejudiced persons? Have they enquired of the respectable makers of the boiler? Have they enquired of those who have boilers in action on precisely the same principle-the Liverpool Water Works Company, for instance? For, if the theory be correct, it must produce similar effects under similar circumstances.

Now, there is a very important and useful consideration arising out of this discussion, and which, otherwise, would be very unsuitably placed in your scientific Magazine. I allude to the adoption of means for judging correctly, how far any system of combustion, or "smoke burning," or arrangement of furnaces, may be effective or otherwise; and which would enable the owners-the really interested parties to judge for themselves, independently of the theoretical views and imaginary statements of patentees. As this is a matter of great practical value, I propose, (though out of the course I had determined on,) in my next communication, to go into the question, and show its absolute necessity.

I am, Sir, yours, &c.

C. W. WILLIAMS.

Liverpool, March 7, 1842.

Erratum. In my last communication, page 187, line 19, for, "from 46°, to 476°," read " from 400° to 476°."

STEAM NAVIGATION OF THE ATLANTIC

LIVERPOOL AND BRISTOL LINES.

Sir, I have just perused your extract from the Bristol Magazine in your number for January 1st, respecting the steam navigation of the Atlantic, and the rival lines of Bristol and Liverpool; and although I think with you that it is true "in the main," yet still it contains much exaggeration, and many of the facts have

1. With respect to the conveyance of the North American mails:-the Editor of the Bristol Magazine would seem to insinuate that the government had made a "patronage job" of it to serve their own interests, and that they had absolutely thrown away 35,0007. of the public money. Now, the facts are these: the government having determined on carrying the N. A. mails by steam, pitched upon Liverpool as the best port in the United Kingdom for the packets to take their departure from, being from its situation nearer to, and in direct communication with Manchester, Birmingham, Sheffield, Glasgow, &c., where about nine-tenths of the letters go from, and also from the great number of American vessels that enter the Mersey, the chief seat of our American trade. Having decided on Liverpool, the contract for conveying the mails was offered publicly, and the British and North American Steam Packet Company offering the most favourable terms, the contract was given to them, and not to a company with a single vessel, sailing from a second-rate seaport to a foreign one.

66

2. With respect to the "wisdom of the government" in thus conferring the contract upon Liverpool :-the government had not only the exigencies of the post-office service" in view, but looking rather farther than the Editor of the Bristol Magazine, they had also an eye to the welfare and benefit of the nation at large; for, in the contract, it was expressly stipulated, that the company should provide four steamers of certain dimensions; and, that in case of war occurring with any foreign country, these vessels were to be manned and armed in the same manner as the navy steam-frigates, and were to be placed at the absolute control and disposal of the government during the continuance of such war. Even if the government had only the "exigencies of the post-office service" in view, what is the result? As far as regards the "speed" of the vessels, we find that the Halifax boats, in fine weather, have usually made the voyage home from that port to Liverpool, in from ten days and ten hours, to eleven days; while the Great Western takes from thirteen to fourteen days, although Halifax is many degrees farther to the northward than New York, and consequently the former

205

boats have to contend with the severer weather, which is generally experienced so far to the northward. As to the remarks respecting the punctuality of the Caledonia, Columbia, &c., their detention when they have been detained has always been satisfactorily accounted for, either from having experienced severe weather, which, as I have before observed, is not so often felt, and never so severely on the voyage from New York, as on that from Halifax, having met with icebergs, which is frequently the case, or else from having been detained by the government authorities to bring home despatches of importance.

3. With respect to the Editor of the Bristol Magazine's remarks regarding the voyages of the Britannia and the Great Western in October last, the causes of the delay of the former vessel are so well known, that it would be quite superfluous for me to make any remarks respecting it.

4. With regard to the delivery of letters via Bristol:-if both the steamers were off Cape Clear at the same time, we will allow that it would take the Britannia even ten hours longer to deliver her letters in Liverpool, than it would the Great Western hers in Bristol; letters from Bristol are absolutely thirty hours in reaching Liverpool by the regular post, that is, if they are posted in the former town on the 21st, in time for the evening despatch, they are not delivered till the morning of the 23rd in the latter town, thus losing twenty hours at least in the delivery. If the difference is so great with respect to Liverpool, it follows that it must be much greater with respect to the other towns I have mentioned.

I have drawn my letter to such a length, that I have hardly room left to make any further remarks. Still, I cannot conclude, without noticing the absurdity of supposing that government would give the contract to a company with a single vessel to convey mails of such importance; when, if an accident occurred to the vessel, the communication between the two countries would have to be suspended whilst she was undergoing her repairs.

Hoping, that in justice to this port, you will insert the foregoing remarks in your able and well-conducted Magazine, I am, sir, yours very truly, A CLERK, Liverpool, February 26, 1842,