« ZurückWeiter »
11 inches deep, and 25 inches wide, faced against a cast-iron packing piece, dovetailed into the nozzle, and jointed with elastic packing. The slides are kept up against the packing pieces simply by the pressure of the steam.
* The exhaustion slides are kept tight by the effects of the partial vacuum behind them, and work against a packing piece on the side nearest to the condenser.
" The steam slides are attached to their rods by knuckle joints, which suffer them to open outwards, should they be acted upon by undue pressure inside the cylinder, thus forming safety-valves.
" The adjustment of the slide is such, that when the piston has descended iths of its path the steam is shut off, and when quite at its bottom stroke, the lower slide-valve is open gths of an inch, and the upper exhaustion slide open 2 inches.
“ The area of the steam passages is 3.25 x 21 68.25 square inches, being in the ratio of 1 to 47:13 of the area of the cylinder.
* The area of the exhaustion passages is 5*25 x 21 110-25 square inches, being a ratio of 1 to 29:17 of the area of the cylinder."
in one, and causes it to rise an equal height in the other leg: a rod of wood, floating on the surface of the mercury in the latter, marks lbs. upon a scale of inches. The bore of the tube must be equal in both legs, other. wise the mercury will not rise so much in one as it sinks in the other, and, as a consequence, will not show the pressure correctly.
“ 'The atmospheric or reverse-valve is added to the boiler to guard against the effects of external pressure, as the steam cools after the fires are let down. It is some. times considered sufficient for this purpose to open the safety-valve, but a reverse-valve is now generally added : it consists of a valve fitted against a seat, and opening inwards, being kept shut by a small lever and weight.”
Steaming Capabilities. [Extract from a letter from Mr. Frederick
Robinson, Mate of the “Cyclops," to Mr. Weale, dated Alexandria, 17th April, 1842.]
“ The steam can be raised from cold water, temperature 60', in about 75 minutes, with about įrds of a ton of coals. After two years' experience, it is found that 24 hours' consumption averages 241 tons, or about 1 ton per hour, equal to about 7 lbs. per horse power per hour, and which, at an average rate of 8.4 miles per hour, leaves the expense of steaming about 38. 10d. per mile, if we use the following prices for the consumable stores, viz., Coals, per ton.......
3d. And these are believed to be the average Mediterranean prices.
“ The maximum speed attained by Cyclops is thought to have been 11 knots, though there has never been more than 10.5 registered in the log-book; this is when in good trim for speed, having about 100 tons of coal on board, and drawing between 15:3 to 15.6 forward, and from 15.9 to 16:3 aft. The average speed in moderate weather, with between 200 and 300 tons of coal on board, and drawing 15.9 forward, 16.6 aft, or thereabouts, is 9 knots.
“ As a frigate she is most serviceable ; and, but for her want of power, could scarcely be improved upon. It is principally in towing heavy ships that her want of power is most conspicuous : her burden, as before stated, is 1,195 tons, while her engines are but 320 horses. Her rate of towing the line-of-battle ships and small threedeckers, (like the Princess Charlotte,) has been 6 or 6.2 knots per hour; and the
The Saline Detectors, “ The Saline Detector applied to the present boilers consists of a glass tube fastened on to the front of the boilers, and open to them below the water level, containing, therefore, water of the same density. Two glass hydrometer balls are placed within it, one heavier than the other, but the weight of both being greater than their bulk of seawater, when containing of salt, they reInain at the bottom of the tube in the first instance. When the evaporation and saturation has continued until the water contains
of salt, the lighter ball rises to the surface, and it becomes necessary to blow out. The second ball is adjusted to rise when the saturation is equal to about so, which is beyond the limits prescribed by practice. The “ blow-out" pipe is carried to within a few inches of the bottom of the boilers, so that the more dense water is ejected ; and when the lighter hydrometer ball sinks again, the blow-out cock is shut.
6. The safety-valve loaded to 3} lbs. per square inch insures the boiler against an explosion ; but the engine-man requires a gauge to enable him to keep up his steam to the proper elasticity, and this instrument consists simply of an inverted syphon-tube of wrought iron, partly filled with mercury, open to the steam at one end and to the atmosphere at the other. The pressure of the steam, therefore, depresses the mercury
expense of taking them to sea, out of Malta ventor of this British application of it was Harbour, has been estimated at 31. 10s. each a Mr. John Shorter, of Wapping Wall, vessel. The fuel used has been chiefly Scotch from whom Mr. David Napier obtained, and Welsh, and, when mired, has been found
at a subsequent period, the particulars to burn well; but if used separately, it has disclosed in the following extractbeen found that there is a difference of nearly
“Mr. Napier having made some experi. one pound per horse power per hour in the
ments with a screw which he believed to consumption, the Welsh being the most ex
have originated with himself, showed it to travagant. It is a difficult matter to arrive
various persons, and thereby became ac. accurately at the wholesale consumption, for
quainted with Mr. Shorter's previous trials; it is a common complaint in the service, that
and having found that person to be living in the quantities of coal stated in supply notes
Southwark, he called upon him at his resi. from the dock-yards always greatly exceed
dence, and was shown a large collection of any estimate or measurement for consump
models of the screw propeller applied in the tion; there being always a great difference between supply and expenditure.”
dead wood, the quarter, the bow, at the
vessel's sides, and, in short, in every possi. Expense of Steam Frigates.
ble position. The screws also were varied “ As the expense of the year 1841 may be in their form, consisting of one continuous interesting, I shall here quote it: it will give thread, of two, three, and four threads, of an idea of the estimate for a steam navy. mere vanes, like a windmill, and of a single “ During the year 1841 the Cyclops' ser
Indeed, Mr. Napier states that he vices were as follows:
appeared to have contemplated every possi. Under Steam.
ble arrangement, and that his models com1462 hours= 10.619 miles ; maximum 10.2. prised most of the modifications now before Under Sail only.
the public. He showed Mr. Napier a num624 hours - 2.95 miles ; maximum 8.2. ber of experiments in a reservoir he had Coals, 1462 tons, at 308.
constructed for that purpose in his work. Tallow, 1830 lbs., at 5d.
shop, by which it appeared that the best Oil, 183 gallons, at 38. 2d.
performance arose from a single blade or Oakum, 183 lbs., at 2.d.
arm projecting from an axis, and this seems 1
to have been the form he used in its adaptaWages.
tion to the vessels referred to in the certifi.
3,589 Other stores, wine and tea, say about 500
cates. The position in which he fixed them
is doubtful, but the impression is that they £11,650
were placed one in each quarter, the axes
passing through stuffing-boxes." Or rather less than 1,0001. for each hundred Marestier, in his memoir on the steam tons burden.''
navigation of the United States, 1824, The second of these Appendices (called described several methods of propelling Appendix D) is devoted to the subject of on the principle of the screw, which had “The Archimedean screw, or sub-ma
been either tried or proposed." A rine propeller,” and is written by Mr. year later, Mr. Samuel Brown, the inElijah Galloway, the author of the “ His ventor of the gas vacuum engine, applied tory of the Steam-engine," and inventor a propeller on the principle of the screw of the paddle-wheel known by the name to a small boat (at the bow) which he of Morgan's wheel, as also of the divided had fitted with his new engineor cycloidal paddle of more rccent
“ With this vessel several trips were made, date.
principally between London Bridge and Mr. Galloway gives first a “history of Battersea, though occasionally below bridge. the invention.' He finds traces of it In this vessel, we are informed, there were in the "Machines et Inventions ap sometimes as many as thirty persons carried prouvées par l'Academie Royale des at once, at an average speed of 6 to 7 miles Sciences," 1727-1731; also, in a work
On one occasion, she passed by Paucton, “on the Theory of the through Battersea Bridge at the same time Screw of Archimedes," 1768 ; and, what as the Diana Richmond boat, and passed is more remarkable, produces document
the current in less time than the Diana, ary evidence of its having been success
though the latter is stated to have been 20. fully applied in the British navy as early
horse power.” as 1802, (by manual power of course,) Tredgold mentions several other par. to move ships of war in action. The in ties by whom the idea of screw propul.
sion was at different times taken up, tried, illustrated by a copper plate, on and abandoned.
large scale, as well as by numerous But though all these facts show that wood engravings.
After this come the propelling power of the screw is “no the experiments made with the vessel new discovery," they prove at the same under the superintendence of Captain time that it had never been turned to Chappell, with the results of which our any practical account down to the recent readers are already familiar. The conperiod, (1836,) when Mr. J. P. Smith clusion which Mr. Galloway deduces brought it so prominently under the no. from these experiments is of rather an tice of the public, by his patents, and by equivocal character. " As far as the his successful experiments with the Ar question,” he says, can be decided by chimedes. Mr. Galloway pays a well such trials as we have enumerated, there merited tribute of praise to the Messrs. can be no doubt that the performance of Rennie, for the active and public-spirited the screw has not been proved to be infepart which they have taken in carrying rior to that of the paddle-wheel.” Neither out Mr. Smith's plans to a successful does Mr. Galloway think it possible to issue. After describing some experi, venture further in the way of opinion, ments which Mr. Smith had made with "until two vessels of the same form and a small model vessel, he thus proceeds— power (one fitted with the screw and the
“ The results of these trials were so satis other with the paddle-wheels) shall have factory as to lead to the formation of a
made several voyages, so as to test their Company under the title of . The Ship Pro-. comparative advantages in various kinds peller Company.' The system of propul. of weather.” And a double experiment sion was, however, so unpopular among
of this sort is, it appears, about to be manufacturing engineers and scientific men
actually made by the Admiralty-orders generally, that it was some time before a manufacturer could be found to undertake
having been given to fit out the Rattler an order to construct the engines and machi
and Polyphemus, two sister vessels, with nery for a large experimental vessel. Messrs.
steam engines of precisely the same deGeorge and John Rennie (sons of the cele. scription and power—the former to be brated Mr. John Rennie) having, however, propelled by the screw, and the latter by witnessed several trials with the little expe paddle-wheels. rimental vessel, and satisfied themselves that Mr. Galloway favours his readers in the invention was one of considerable promise,
the meanwhile with a mathematical not only undertook the order, but contri. investigation of “the relative value of buted largely towards the necessary funds the paddle-wheel and the screw, as refor carrying out the designs of the Company. gards the proportion which the propellIt may be interesting to state that an inven ing effect bears to the power employed.” tion which has been so far established that
His conclusion on this head isit has now become a subject of honourable competition to discover and apply the best
“ That when the paddle-wheel is at an
ordinary immersion, and the slip equal in arrangement of machinery and form of propeller, was, at that period alluded to with
both systems, the advantage is somewhat in ridicule, or at best with expressions of re
favour of paddles ; but that when a vessel gret that Messrs. Rennie should sport with
with paddles is deeply laden, or rolling contheir reputation and a Company with their
siderably in a sea-way, so as to immerse the capital in so hopeless a project. Such facts
wheel beyond a certain dip, or when the as these cannot be considered unworthy of
screw is so constructed as to have less slip notice, as showing the vast difficulties which
than the paddle, the advantage is in favour
of the screw. And further, as a beam wind oppose the prosecution of a new discovery and as proving that the successful practical
necessarily depresses the lee wheel so as to application of a mechanical invention is at.
cause it to be disadvantageously immersed, tended with as many obstacles, and requires
a steamer with paddles can only partially
avail of such a wind ; while with the screw the possession of a quality of mind, almost as rare and as valuable to the community as
there is no such limitation, and canvass can the highest powers of invention.”-p. 12. made use of in Craven's Chimney Sweeping MaThe machinery of the Archime
chine, of which an account is given in our 990th
Number, and which is there supposed by us to be des is then very fully described, * and
new, and commended as a contrivance "of great
ingenuity, and applicable to many other purposes." We observe, by the way, among this machinery; Not the first instance, by a great many, of a good a "peculiar coupling,” as it is styled, (Fig. 10,) thing being invented by two different parties, which happens to be precisely the same as that wholly independent of each other.
consequently be used to the same extent as the disposition of the water, according to in a sailing vessel. The advantage possessed the first law of motion, to continue in the by the screw in this respect was clearly same state of rest or movement. In the proved in the trials between the Archimedes case of a vessel the water must fall in to fill and Her Majesty's steamer Widgeon, where up the cavity which the vessel leaves, and in the latter vessel was superior to the former doing so, flows after the vessel in her onin calm weather or a head wind, but inferior ward course. The velocity of such current with the wind a-beam.”' p. 37.
is decreased by constructing the after body The "slip or recession of the screw,”
with finer lines, which would allow the water Mr. Galloway considers to be almost to fall into the space more gradually, and entirely a question of magnitude; for
more from the sides of the cavity than when " if we increase the diameter without
the form is full ; but such a following cur
rent must ever exist even in the most delialtering the pitch, we reduce the slip without increasing the velocity at which
cate form. The propeller, therefore, being
placed in a position where such a current it would be required to drive the screw."
exists, has a force acting against its surface, The increase of diameter would of course
so that, although it really slips through the increase the surface friction ; but not to fluid against which it exerts its power, its such an extent, Mr. Galloway thinks, as motion in relation to the surrounding and to make the total friction greater than in inactive water seems to coincide with the the case of paddle-wheels. But whatever action of a screw in a solid body, and, as in the amount of the “slip " may be, it the instance alluded to, even to exceed the would seem, from a very curious fact, progress which such a screw would make.” which has recently come to light in the course of some experiments made at
The number of threads which should Bristol by the parties concerned in the
be given to the screw, is one of the many erection of the Great Britain, (late points relating to the present subject still Mammoth,) that it may be more than
remaining to be determined by expericompensated by a new source of power ment; but Mr. Galloway mentions that derivable from the form given to the "a sensible improvement was produced stern.
in the speed of the Archimedes by sub“A series of trials of the Archimedes have
stituting the double thread for the ori. been made at Bristol with different kinds of
ginal single one." propellers, in which the form and number of
In the case of the Archimedes there was the threads were varied. The writer has not been permitted to publish these experi: longitudinally in a hole cut in the dead
but one screw employed, which was placed ments, as they were not considered sufficiently accurate for that purpose.* In one of
wood immediately before the rudder. them the vessel advanced a greater dis
Instead of this, it has been proposed to tance than the screw could have propelled
make use of two screws, one at each side her in still water, or, in other words, if the
of the dead wood, or
at each screw had been worming its way through a side a-midships. Mr. Galloway thinks solid body the vessel would not have ad. rather favourably of the former plan, but vanced so far as she did in the experiment entirely condemns the latter. alluded to. This appeared so paradoxical The means of communicating motion that the author questioned its accuracy, but from the engine to the screw are investiinquiry has confirmed the fact, while further
gated under the three different heads of investigation has furnished a probable reason Toothed Wheels,-Bands or Ropes,for the seeming anomaly. "If we observe the motion of vessels fuces. The "toothed-wheel” mode, which
and Contact by Pressure of Smooth Surthrough the water with full after bodies, or, what is the same thing, if we notice the ef
was that adopted in the Archimedes, Mr. fect of a current acting against the piers of
Galloway admits to be “ not a desirable bridges, we find in the immediate wake there arrangement," because of the liability of is a quantity of fluid which approaches a
the teeth to get stripped off “ by any state of rest, and round which the active cur sudden change in the resistance or from rent forms an eddy. In such cases, a piece imperceptible decay.” “Bands" of all of floating matter will sometimes retain its sorts he objects to because of their “liaproximity to the vessel or pier for a consi- bility to stretch," and of the rapid de. derable time. This obviously arises from struction resulting from the employment • The results as regards speed were decidedly in
of tightening pulleys; and “contact by favour of the original screw of the Archimedes, pressure of smooth surfaces” (more com.
monly called adhesion) if obtained by a " the power of the engines.” This we peculiar method of his own, now for the must take leave to say is not investigafirst time submitted to the public, but tion after the manner of Tredgold, but for a description of which we must refer palpable hap-hazard assertion after the to the work itself, he seems to consider worst manner of quacks and empirics. the most unobjectionable of any.
Mr. (George) Rennie's Conoidal ProWe entertain a very favourable opinion
eller is treated more amusingly, though of Mr. Galloway's “own;" but at the same
we cannot say more justly or philosophitime we feel bound to remark that he has done any thing but common justice
cally. It consists, Mr. Galloway tells us,
of an inclined plane wound round a to the “band” system. All bands do not
logarithmic cone or spire"-meaning to stretch, not at least at any strains to which
say (we presume) of an inclined plane screw shafts can ordinarily be exposed: produced by a straight line wound round the metal bands, for example, of Newall; a cone. It exhibits, moreover, accordand if the existing fact were otherwise, it
ing to Mr. Galloway, certain " distinwould not, we apprehend, be difficult to
guishing features, which are founded on a devise a band that would be as unstretch
close observation of the forms which Naable as any solid cylinder ever produced, ture has given to the impelling organs of
Again; bands, when they do break, those of her creatures which move through can be readily repaired or replaced, while the waters ;" but though he admits, (so wheels stripped of their cogs, or of any candid is he !) that it is “a safe prinnumber of them, are either beyond repair,
ciple to assume, that the Great Archior must remain as they are till the vessel
tect has adopted the very best forms in returns to port. For these reasons we
all his works," he cannot bring himself consider the band system to be indisput to allow that Mr. Rennie's “ close obably superior to the toothed-wheel one,
servation" of this very best of all posand one, moreover, which will answer sible models has been of any practical well under all circumstances; though, It does not suit him, (apparently,) according to Mr. Galloway, and for the
to say that it has, and he does not like to sake (we cannot help suspecting) of better
say flatly that it has not, (which, howclearing the way for “ my own,” he
ever, is evidently his real opinion). But places both in the same category of in as it was requisite he should say someefficiency.
thing on the subject, (this à la Charles Mr. Galloway gives by way of supple. Buller,) he treats his reader to the folment to " the Archimedean Screw,”
lowing precious piece of seeming wisdom : descriptions of “Ericsson's Propeller," “Mr. Rennie's Spriral Propeller," (i. e. “The difficulty which we have to encounthe Conoidal-its paternal and much ter in our imitations arises generally either fitter name,) “ Hunt's Propeller," from our not understanding all the purposes “ Blaxland's Propeller," "Mr. David of the arrangement, or from our inability to Napier's Propeller," "Captain Carpen
Captain Carpen- apply them in the same way, or give them ter's Propeller,” and “ Modification by the same properties. Thus the propelling the author,” (another design of "my
effort of the fish is given out by an alternatown.")
ing action, and a form similar to his tail “ Ericsson's Propeller," appears to
may not be equally well adapted to rotatory have been a bit of a puzzler to our au
motion. The fish is also endowed with life,
and his tail is elastic, so that he suits it to thor. The average performance of the
the motion of the fluid in such a manner Archimedes during the trial under Capt.
that the form may lose its best properties if Chappell was about 8} iniles an hour; but
not thus regulated and changed at the will the Robert Stockton, a vessel fitted with of the animal."'-p. 54. " Ericsson's Propeller," "ran (on the Thames, with the tide) 9 miles in 35 And so, because Mr. Galloway cannot, minutes," =more than 15 miles an hour. or affects not to understand how a numTo account fairly for this without giving ber of rectilineal movements can be conaltogether the go-bye to the “ Archi verted into a rotary one, (that is, practimedes" was a matter of difficulty; and cally speaking,) and fancies, or affects to so, to get rid of the difficulty, Mr. Gal- fancy, that there is something in the loway places the whole difference to the " will ” of a fish quite independent of its account of some possible difference in “ tail,” Mr. Rennie's most scientific and