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THIRD NOTICE.

The

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with short canals of large dimensions at in of the pressure on a mercurial column. The tervals precluded the use of the paddle-wheel pressure of such a column varying directly for the freighting business; but the introduce with its elevation or depression, follows the tion of the propeller places the whole trade same law as the elasticity of a bar; whence under the control of steam."

it follows, that if any pressure be thrown at once, or instantaneously, upon the surface of the mercury, the variation of the height of

the column will be twice that which it would MOSELEY'S MECHANICAL PRINCIPLES

receive from an equal pressure gradually acENGINEERING AND ARCHITECTURE. cumulated. Some singular errors appear to

have resulted from a neglect of this principle

in the discussion of experiments upon the The attention of the student is next di.

pressure of steam, made with the mercurial rected to the “ Strength of the Materials” of column. No such pressure can, of course, which machines and buildings are composed. be made to operate, in the mathematical elasticity " of bodies is shown to

sense of the term, instantaneously; and

the term gradually has a relative meaning. depend on this law, that “the force neces

All that is meant is, that a certain relation sary to keep a body extended or

must obtain between the rate of the increase pressed is proportional to the amount of the of the pressure and the amplitude of the extension or compression; so that each

otion; so that, when the pressure no

longer increases, the motion may cease."'equal increment of the extending or com

Page 490. pressing force produces an equal increment

The general rule laid down by the Proof its extension or compression.” From an

fessor is, that the work expended extensive series of experiments made by Mr.

elongation of a bar should vary only as the Barlow, on iron bars of different qualities,

square of the strain and the length of the bar, he deduced the conclusion, that a bar of iron

and inversely as the area of its section ; of mean quality may be assumed to elongate

and, by applying this rule, the engineer may by 100 millionth parts, or the 10,000th part

always determine the amount of work ex. of its whole length, under every additional

pended prejudicially upon the elasticity of the strain of one ton per square inch of its sec

rods used for transmitting work in machinery tion. The French engineers of the Pont des under a reciprocating motion-pump-rods, Invalides assign 82 millionth parts to this

for instance. A sudden effort of the pressure elongation; but Professor Moseley thinks it

transmitted in the nature of an impact may probable that these experiments were made

make the expenditure of work double that upon iron of an inferior quality. Cables of

which the above rule shows to be necessary. iron wire elongate, according to Vicat, by In treating of rupture by elongation, Mr. 91 millionth parts; and bars of oak, accord

Moseley is led to a discussion of the theory ing to Minard and Desormes, by 1,176 of Suspension Bridges. As these structures millionth parts. The strain, however, in all have been hitherto commonly designed, the these cases, is supposed to be applied by chains have had one uniform section. The equal increments; for it is further establish author demonstrates that this is “ false in ed, that if the whole strain, corresponding principle;" and that, if it is required to to any particular degree of elongation, be build a bridge of " uniform strength," and put on at once, twice as much work will be therefore with “ the greatest economy of done upon the bar as is expended on its material," the area of the section of the elasticity. Of this Mr. Moseley gives the chains should “ increase from the lowest following striking illustration, to which we point towards the points of suspension where would beg to invite the particular attention it is greatest." The readers of our work of all concerned in the working of steam will instantly recognize, in this important engines.

conclusion, the distinguishing principle of “ The mechanical principle involved in

the suspension bridge invented by Mr. this result has numerous applications ; one

Dredge, which we have so often had occasion of these is, to the effect of a sudden variation to bring under their notice; and will, doubt

were

less, be as much surprised as we have been, section, the mathematicians never discovered (à surprise, on our parts, not unmixed with that there was any thing wrong in that pracsorrow,) to read the following note, which tice, but, on the contrary, made it the found. Mr. Moseley has appended to his enuncia ation of all their theories on this subjecttion of the new principle.

theories which, proceeding on false data, “ This variation of the section of the were, of course, good for nothing ; and bechains is exhibited in a suspension bridge cause, if Mr. Moseley has been able to prorecently invented by Mr. Dredge, and ap

duce a simpler and truer theory of the suspears to constitute the whole merit of that invention.—Page 543.

pension bridge than any of his predecessors,

it is entirely owing to the individual whom The tone of this note is palpably slighting it is the tendency, if not the object, of the and disparaging; and, exactly to the extent

foot-note we have quoted to discredit and which it is so, is most unjust. True, Mr. injure. Dredge did but discover that the section of the

We gladly pass from the case of Mr. chain should diminish from the highest to the

Dredge and the Suspension Bridge to anlowest point; but, in discovering that, he

other, in which, though strikingly and esdiscovered all that is confessedly of most sentially alike in all its circumstances, Proimportance in the erection of structures of

fessor Moseley has seen fit to pursue a this class. He discovered this principle, too, directly opposite course. We allude to that before any thing similar had been evolved, of Mr. Eaton Hodgkinson, and his experieither by the practice of engineers or by the ments on the Strength of Columns. Here, cogitations of mathematicians. What one of

as in the case of the Suspension Bridge, the the first of engineers, Telford, missed, in the “ Mathematics and Mathematicians greatest of all his works, a person wholly all at fault, till “ Practice and Practicians" unknown before to the engineering world came to their aid. “ The hypothesis," Mr. has had the good fortune to find; what all the Moseley admits, “ upon which it has been profound learning of the Whewells and the

customary to found the theoretical discussion Powells of the schools, had failed to bring to of the subject, is so obviously insufficient, light, has been revealed to the world through and the results have been shown by Mr. the humble medium of the self-taught ex Hodgkinson to be so little in accordance perimenter of Bath. It may be that the with those of practice, that the high sanchappy thought came to him, not through a tion it has received from labours such as long vista of mathematical symbols, (as, in those of Euler, Legrange, Poisson, and Natruth, but few happy thoughts come,) but vier, can no longer establish for it a claim to simply from contemplating the taper form of be admitted among the conclusions of science.his fishing rod; but surely it is not for a Again—" for all the knowledge on this subfollower of the illustrious observer of the fall ject, on which any reliance can be placed, of the apple to sneer at Mr. Dredge on that the engineer is indebted to experiment." account. Mr. Moseley does not fail to And farther" In treating of the strength point out in his Preface, (page xvi.,) the of columns, I have gladly replaced the ma. beautiful simplicity which the principle of thematical speculations upon this subject, the diminishing section has introduced, for which are so obviously founded upon false the first time, into the theory of the sus data, by the invaluable experimental results pension bridge ; and common justice, if not of Mr. E. Hodgkinson, detailed in his wellgratitude, demanded at his hands a frank known paper in the Philosophical Transacrecognition, in the same conspicuous place, tions for 1840." For that paper the Royal of the claims of its discoverer. We say gra Society, with excellent judgment, awarded titude, and repeat the word emphatically ; to Mr. Hodgkinson the Royal Medal ; and because it is a curious fact, that, as long as possibly it may be owing to that circumengineers continued to make the chains of stance that Mr. Moseley sees a merit in the their suspension bridges with one uniform " Practician " Hodgkinson, which is so dimly

discernible to him in the clever, but un

WOOD-PAVING. medalled “ Practician ” Dredge.

Sir, -To arrive at truth, it is necessary While adverting to the services which to look at every side to a question; and practicians have rendered to science, we

if the letter of " Junius Redivivus" were must not here omit to quote the very proper

left unanswered it might lead us from

that desirable point. He states that in notice which Mr. Moseley takes of the share

1834 he gave three several reasons for which another eminent individual of that doubting the success of wood-paving, class had in Mr. Hodgkinson's experiments. founded on the assumption, that none

“ The experiments were made at the ex but the hexagon block would be used; pense of Mr. Fairbairn, of Manchester, by all which reasons have proved erroneous, whose liberal encouragement the researches How, indeed, should they prove otherof practical science have been in other re wise ? What can the swelling of blocks, spects so greatly advanced.”—Page 578. or the rotting of blocks, or being stolen

Let us now see which are the chief prac like farmers' fences, (the three reasons, tical results for which we are indebted to have to do with the shape of the blocks ? Messrs. Hodgkinson and Fairbairn. Leaving

He finds, after a lapse of eight years, out the mathematical formulæ in which the

there are good reasons why wood-paving

should become general; and he is right Professor has, (for his scholarship's sake, we in his conclusion, but not so in his views as suppose,) enveloped them, they are these : to carrying out the improvement; and as

“ In all cases the strength of a column, every error in so important a question is one of whose ends was rounded and the other calculated to do some harm, I will trouflat, was found to be an arithmetic mean be ble you with a few observations. tween the strength of two other columns of The alleged drawback of the slipping the same dimensions, one having both ends of horses, has proved as fallacious as all rounded, and the other having both ends other fears on this subject. It is a fact flat.

now rarely questioned, that horses used to “ The above results apply only to the case wood can run as securely as on stones ; in which the length of the column is so

nor will it be difficult to understand this, great, that its fracture is produced wholly

if we recollect our own awkardness, when by the bending of its material; this limit is fixed by Mr. Hodgkinson, in respect to co

for the first time trying to walk the ice lumns of cast-iron, at about 15 times the

on skates. Besides, the alteration in the diameter, when the extremities are rounded,

construction of the shoes is at this moand 30 times the diameter when they are

ment kecping pace with the paving. flat. In shorter columns, fracture takes The swelling of the timber, stated by place partly by the crushing, and partly by your correspondent to be an evil

, is prored the bending of the material.

to be the very contrary. In the instance “ It was found that the strength of co of St. Giles' Church, the primary evil lumns of cast-iron, whose diameters were was, that the patentee depended on the from one-and-a-half times to twice as great curb-stones for abutments, to form a in the middle as the extremities, were stronger, sort of arch, leaving no room for swelling. by one-seventh, than solid columns contain

Such disruption has never occurred in ing the same quantity of iron, and of the

any other instance, nor will it ever occur same length, when the extremities were

again unless from a similar cause. I berounded; and stronger by one-eighth, or one

lieve no one has more studied this subninth, when the extremities were flat, and rendered immoveable by discs.

ject than myself, and I can safely assert “ Calling the strength of the cast-iron

that London does not contain a yard of column 1000, the strength of the wrought paving, on any principle, that has not iron column will, according to these experi

been improved by the swelling in the ments, be 1745 ; that of the cast-steel co working of the blocks to their final setlumn, 2518 ; of the column of Dantzic oak, tlement and adjustments, in assisting to 108.8; and of the column of red deal, 78.5. fill up and form mass that can be ob.

tained by no other means. In fact, it “ It results from these experiments, that has proved a friend to wood-paving most the strength of short columns of wet timber desirable, and certainly most unexpected. to resist crushing is not one-half that of columns of the same dimensions of dry correspondent consists in stating that the

The principal error, however, of your timber.” – Page 579.

most approved plan now is with an angle (To be concluded in our next.) of 45° to the horizon. It is a fact which

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OF THE THAMES.

I thought every man was acquainted with, which I have recommended for the conthat we have not one yard in London at stant self-adjustment of the surface of the 45°, nor (except a few yards laid within mercury within the cistern to that within the past month) any inclined block at the tube, as indicated by the scale and any other than between 639 and 64o. vernier, no results can be obtained that Indeed, the only inclined blocks ever yet will not require subsequent correction, laid down are those on Parkin's patent, even although the tube itself be an accutaken out Oct. 1839, and Count de rate cylinder. Lilse's, about three months after. A If your scientific readers admit the pavement with an angle of 45° would truth of these statements, they may, of present so much of the side of the fibre, course, (provided my principle, so far as that a horse could not stand on it any I have described it, be fully embodied in more than if the grain were parallel to the barometers constructed by Mr. Readthe road; and every one that has trodden man,) resolve for themselves whether on a wet polished plank can form some they would rather estimate the differidea of that.

ences of atmospheric pressure by weight, The last error, is to suppose that groov as indicated by a steel-yard or other ing will diminish the wear to any ma contrivance, or by measure, as shown terial degree, especially when it is proved by a well divided scale and vernier. that good wood will wear but one third Believe me, very faithfully yours, as fast as stone, (about half an inch in seven

Chas. THORNTON COATHUPE. years.) This, however, can be the case Wraxall, near Bristol, December 5, 1842. only when a perfectly uniform and smooth surface is maintained; then there is no concussion, and pressure will make

MAGICIAN" the wood harder.

A new iron steamer has been lately I am, Sir, your subscriber,

T. H. B.

launched in the River, 'yclept the Magician, which, if all be true that is reported her,

has not been unfitly named. She has been READMAN'S BAROMETER.

built by Messrs. Ditchbourne and Mare, and Sir,-Your remarks upon my commu.

engine-fitted by Messrs. Penn and Son. nication relative to barometers, inserted in the October Part of the Mechanics'

Her burthen is 360 tons, and her lines beau. Magazine, although not altogether strict

tiful; her engines are of 110 horses' power. ly correct as to dates, were, nevertheless, The paddle-wheels are on Morgan's feathersufficiently satisfactory as regarded their ing plan. A Woolwich correspondent, who intended purpose. In the November

supplies us with the preceding particulars, Part of your Magazine, Mr. Readman,

affirms that she goes “upwards of fifteen admitting the principle of suspending, or placing the cistern of a barometer on

miles an hour;" and another 'longshorea spring or balance, to be the only point

man states, in confirmation of this surprising in which our inventions agree, claims speed, that the Magician started from Wool. the extension of this principle to the wich an hour after a Government steamer of weighing the mercury in the cistern,

320 horses' power, and within another hour which he considers to be a better test of

overtook and passed her! atmospheric pressure, than that of estimating the length of the column of mercury within the tube.

MR. BAGGS's CARBONIC ACID ENGINE. In the present instance, I am not inclined to admit that any practical advan

Sir, I am not aware if it has ever been tage can arise from Mr. Readman's sub

suggested to Mr. Bagg, the ingenious institution of weight for measure ; for,

ventor of the Carbonic Acid Engine, deunless the tube be so selected or prepared, attempt its introduction on the common

scribed in No. 1005 of your Magazine, to that its bore shall be accurately cylindri; road, where I should imagine it would be cal within the limits of the mercurial

more likely to be of importance than on a range, his method of weighing would be railroad, comparatively speaking, as obviatevidently imperfect; and, unless his cis- ing many of the (apparently) insuperable tern be constructed upon the principle defects of a common road steam-carriage.

First, it would be of greatly less weight; secondly, not liable to so much damage from jolting; and, thirdly, not liable to a loss of power while stopping.

I a
am, Sir, &c.,

S. M.

NOTES AND NOTICES.

New Brcakwater.-The steamer Monkey recently arrived in this port, having in tow a cylinder of large dimensions, and freighted with heavy iron work, forming the material for a section of a noating breakwater, the invention of Captain Groves, late of the Rifle Brigade, which is to be moored experimentally in the bay. Judging from its appearance, there is nothing complicated or diflicult in its construction. The whole is of iron. The cylinder sustains a grating, attached to it by hoops, and firmly braced by stays passing round the cylinder, and very securely bolted into the bottom of the grating. The draught of water will be about 12 feet, and it will be moored broadside to the sea, both to landward and seaward. Nautical men say that the doubtful part of the experiment is the ability of the moorings to resist the immense strain to which they will be subjected. Although this experiment is made with the sanction and under the auspices of Government, Captain Groves incurs the whole expense of the work, with the exception of the moorings, which were furnished from Sheerness Dockyard.Dover Telegraph. The following notice of the actual mooring of this breakwater has since appeared in the London Papers. " Dover, Dec. 6.

The experimental floating break water, constructed by Captain Groves, has been this day moored in Dover-bay, in 7 fathoms water. It is an iron cylinder, painted black, 50 feet long, 8 feet in diameter, and riding about 4 feet out of the water, nearly a-third of a mile from the pier, bearing E.S. E. from the light on the south pier. A spar, 20 feet high, with a red flag and a bell, will be attached to it.”

Melhod of Oblaining Copper and Silver in the most Minute State of Division.- A solution of sulphate of copper is heated to the boiling-point, and precipitated with distilled zink. The precipitated copper is then separated from the adherent zink by diluted sulphuric acid, and dried by exposure to a moderate temperature. From recently precipitated chloride of silver an exceedingly fine silver-dust may also be obtained by boiling it with water acidulated with sulphuric acid and zink.-Boettger's Beitrage.

Microscope Extraordinary.- A new microscope, of astonishing magnifying power, has just been added to the admirable collection of instrument the Polytechnic Institution. Its highest power magnifies an object 74,000,000 times. The wings of the locust, the tica, the house spider, the sting of a bee, &c., fill the whole field of view, being twentyfour feet diameter. The eye of the fly, containing 750 lenses, is distinctly shown, and appeared like a large patterned carpet, and the various animalculæ in water, &c., look like enormous land animals of the most grotesque shapes. The instrument was made by that eminent optician Mr. Carey.

A Railway entirely of Iron.-in consequence of the intended junction of the Liverpool and Manchester with the Leeds and Manchester Railway at Hunt's-bank, a distance of some 200 or 230 yards will have to be executed by the Bolton Railway Company. It will be formed entirely of cast-iron, and will be about eighteen feet above the level of the pavement; to effect which, fifty-one immense cast metal beams will be required, each weighing

about seven tons, and a similar number of pillars, each weighing five tons. Besides this, the entire length and breadth of the road will have a complete cast metal flooring. The estimated weight of the whole is 1030 tons, exclusive of the weight of the wrought-iron and the rails. The railway will be formed in the centre of the street, leaving a carriage road on each side. The design is beantiful; and the work, judging from appearances, will be of the most substantial description.--Mining Journal.

Prevention of Spontaneous Combuslion.-A letter has been received at Lloyd's, from Dr. William Bland, on the subject of spontaneous combustion of wool in ships. The principle of Dr. Bland's system of prevention is the manufacture of carbonic acid gas on board when required, which, by its specific gravity, would subside among the wool, displacing the atmospheric air. He states that 400 lbs. of carbonate of lime, as whitening, chalk, or the poorer marbles, yield about 180 lbs. of this gas, which would fill a space of 20,000 cubic feet, or 500 toos by measurement. The mode of application, he advises, is to place a cask in every hold, perforated two-thirds the height with a hole an inct in diameter, and lined with lead to that height. Into the head of each cask a metallic tube is to be placed, leading from the deck, and protected by a wood casing; each cask to be provided with the necessary quantity of the carbonate, and when required for use, pour down a requisite quantity of sulphuric acid, diluted with four or five times its weight of water, when the carbonic acid gas would disperse to every part of the hold.

Electro-Carbonic Battery.--Some months since, being engaged in experiments with Grove's flat. celled battery, some of the prominent defects of form, construction, and expense, seemed to me to be remediable by another mode of construction, and the use of a cheaper negative element. About tbe same time, I learned that Berzelius had, in a letter to Dr. Hare, given an account of a battery where coke was at once the negative element and the containing vessel for the nitric acid. I have since made many experiments, and now give the result, which seems most promising. Natural plumbago, or the mixture of it with sand, such as is used in the manufacture of crucibles, gives the form of carbon, which is at once the most effective, cheap, and manageable. A battery was constructed of six cylindrical members of native plumbago, each element one inch in diameter and two inches high, placed in nitric acid of the commercial strength, contained in a cylindrical cup of porous queen's ware, and opposed by a circular zink element analfamated. The connexion was formed by a wire dipping from each zink into a mercury cup excavated in the top of the plumbago cylinders. This battery of six members gave results which were highly satisfactory. In decomposing power, it accomplishes more than 100 pairs of zink and copper of six inches square each. It gave five cubic inches of the mixed gases of water in less than fifty seconds, or one cubic inch in twelve seconds. It also maintained for nearly an hour, at full incandes. cence, fourteen inches of No. 30 platina wire, coiled into a spiral. In all other modes of exhibition it shows a proportionate power.-B. SILLIMAX,Jux, : American Journal.

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INTENDING PATENTEES may be supplied gratis with Instructions, by application (post. paid) to Messrs. J. C. Robertson and Co., 166, Fleet-street, by whom is kept the only COMPLETE REGISTRY OF PATENTS EXTANT from 1617 to the present time).

LONDON: Edited, Printed, and Published by J. C. Robertson, at the Mechanics' Magazine Office,

No. 166, Fleet-street. -Sold by W. and A. Galignani, Rue Vivienne, Paris;

Machin and Co., Dublin; and W. C. Campbell and Co., Hamburgh.

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