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plying a small cock to the pipe, near its entrance to the condenser, the engineer can at all times ascertain the temperature of the injection-water, and, by its circulation and purity, that the pipes are free from injury. These will be made of the best stout copper, so as to be aburdantly durable, and will, in fact, require repair much less frequently than the copper sheathing of the vessel. It will be seen by the position of the pipes, that they are so embayed as to render it almost impossible for them to receive an injury, unless it be of such a nature as would be equally injurious to the vessel; but in the event of any unforeseen accident occurring, as the old injection-passage and discharge-pipe from the hot well will be left free to act, the engineer has merely to turn on the injection-water, and the same process will go on as if they had not been attached. Thus it is that the simplicity of the means employed; its durability, and consequent cheapness, as well in its first cost as afterwards; the little liability to derangement; and, should an accident happen, the momentary readiness with which the old plan can be resorted to; together with the principle remaining unaltered in the application-render such a mode of preventing encrustation particularly deserving the consideration of all who are interested in steam navigation.

Many attempts have been made to prevent encrustation, by condensing without the usual jet, and although the plans hitherto adopted have been eminently successful-so far as the prevention of the encrustation is concerned-yet the best of them has been by means so expensive, so complicated, so liable to derangement from the numerous joints, occupying so much valuable space, and adding so much to the tonnage of the vessel, as to render even encrustation preferable, in most cases, to such a remedy. The mere circumstance of a good vacuum-being produced, can be no test of the effective power of the engine, unless the means employed to produce it be also taken into account. Dr. Lardner, in his recent work on the Steam-Engine, has, with his usual discrimination, detected this fallacy. There is no difficulty in creating a perfect vacuum when a much larger airpump than is used in injecting engines is employed; but it follows, that as this is necessary for non-injecting engines, as

well as an extra and powerful force-pump to keep up a stream of cold water in the cisterns, they must be burdened with additional duty to perform, from which injecting-engines are free, consequently that the quantity of power uselessly expended in producing the vacuum and doing this extra duty deducts just so much from the effective power of the engine. Nor is it possible to effect condensation with an air-pump of the same capacity, in so instantaneous and effectual a manner, without the usual condensingjet, whatever may be the means employed, or how great soever the extent of metallic surface exposed. The opinions of all scientific and practical engineers have long been decided upon this point, for it is impossible for steam to be brought so immediately in contact with a cold surface, however minute may be the divisions to receive it, as it will be by meeting with a stream of cold water dashed amongst it, every separate particle of the water taking hold of a portion of the steam and blending intimately with it.

Condensing without the jet was long tried by Mr. Watt, but was at length abandoned on account of its inferiority, and it has not since his time been revived, until of late years. In a letter from Mr. Watt to Mr. Smeaton, dated the 24th of April, 1776, he thus speaks of the discovery of condensation by injection, and of its vast superiority:-" I have made considerable alterations in our engine lately, particularly in the condenser, for which we have substituted one which works by an injection. In pursuing this idea I have tried several kinds, and have at last come to one which I am not inclined to alter, which operates beyond my ideas in point of quickness and perfection." And the vast superiority of this mode, verified by time and experience, have amply borne testimony to the usual sound judgment of Mr. Watt.

It is scarcely necessary to observe, that the disadvantage attached by some-now first discovered after an experience of more than sixty years-to injectingengines, from the supposed liability of the condenser and air-pump becoming choked with injection-water, however feasible it may appear in theory, can scarcely ever occur in practice. Independently of there being a very accurate index to marine-engines, by which the supply of injection-water can be regu

keep the two plates about 3-8ths distant from each other. There is a slide 2 on the top of the upper plate, similar to, and for the same use, as the eccentric chuck-slide. The wheel 3 is fixed on the face of the puppet (any size or number of teeth); 4 is a wheel that works in fig. 3, and carries fig. 5 on the same spindle, but fig. 5 works between the plates, as does fig. 6, which works in it; fig. 7 works in fig. 6, and carries the wheel fig. 8 on the same spindle in the front of the upper plate, and works in the large wheel fig. 9, to which the work is fixed. The line in the centre, fig. 10, is the screw in the under plate to screw the chuck to the mandril of the lathe. Fig. 11 is a large screw in the centre of the wheel fig. 9, for fixing the work to the wheels. Nos. 3, 4, 8, 9, may be of any size or number of teeth. The slides 12

and 13 are for the purpose of bringing the different size wheels to work together.

Sir,-As you have been kind enough to insert my idea of a life-preserver (see p. 135), I send you a sketch of the small tube therein mentioned.

Fig. 1. A is a tube one inch in length, tapering one quarter to one-fifth of an inch; B, a raised rim to prevent its slipping in when fastened. The dotted line shows the size and shape of the bore. The tube to be made of bone, ebony, ivory, or brass, as may be convenient.

Fig. 2. A is a brass bar, firmly secured to the stopper B, the dark part of which shows a washer of liquored leather; C, a brass nut with which to tighten the stopper when the bag is inflated.

Fig. 3 shows the face of the nut, hav

ing four holes in it to allow an entrance to the air.

Fig. 4 shows the whole complete, with A a knob to keep the nut on.

I am, Sir, &c.

CAMPO-BELLO.

NEWTONIAN THEORY OF THE TIDES.

Sir, I have no wish to take any active part in the controversy on Mr. Macintosh's Electrical Theory of the Universe; my only motive is to correct a mistake which your correspondent Ursa Major has fallen into. He says (No. 666, p. 93),

For example, what can appear more plausible than the theory of the two tides when explained upon electrical principles? The paradox of the tides has always formed a most formidable objection to the doctrine of universal gravitation, to which even La Place himself could never devise a satisfactory auswer," &c. I should like to know what part of La Place's works Ursa Major alludes to. He will find nothing of the kind in the Mechanique Celeste, for in both the 1st and 4th books of that work, when treating of the motion of fluids and the tides, La Place has there demonstrated, that when the sun and moon cause the ocean to swell to places under them, there is also a high tide at the same time in that part of the ocean that is diametrically opposite; and all this he has done in strict accordance with the principles of universal gravitation. But La Place was not the first who made this discovery. Newton himself, although he left the lunar theory, and consequently the theory of the tides, in an unfinished state, has still traced the grand outlines of the lunar theory and that of the tides in the 3d book of the Principia. The Academy of Sciences at Paris selected this difficult part of phy sical astronomy, namely, the theory of the tides, for investigation in 1740. Among the great competitors who contended for the prize, the successful ones were Euler, Maclaurin, and Daniel Bernoulli. The masterly investigation which our countryman, Maclaurin, gave of this difficult problem may be seen in his "Treatise of Fluxions." Since that period every writer of eminence in physical astronomy has demonstrated the same thing; and all their demonstrations are founded upon the unerring principles of

Sir, It is again attempted, it seems, to twist the crooked Patent Law into Mr. some conformity with justice. Mackinnon has undertaken the task; but, I fear, is likely to endure the disappointment of those who begin their business at the wrong end. Until the fundamental principle of the patent law is changed, I conceive there cannot be either security to inventors, justice to the public, or permanence in the law.

Several of the proposed enactments are entitled to the credit of diminishing expense and delay. To render Letters Patent for England valid over Scotland and Ireland also, on simply enrolling additional specifications for those kingdoms

to reduce the stamp-duties to 24-to substitute temporarily the signature of either of the Chief Justices for the King's signature and to give protection to the inventor from the date of his petition→→ are useful alterations in the practice of the system, if its principle is to remain unchanged; but much more than this ought to be accomplished—and might be, were the fundamental error, that a pa tent confers a privilege, exploded, which it must be before the law can rest long in any one attempted state.

It is a misfortune, and not a small one, that patents for inventions have descended historically as arbitrary grants of privilege. While inventions were yet rare, and monopolies granted by Royal favour were yet common, the most convenient, perhaps the only practicable, mode to the inventor of securing the fruits of his labour was to beg a monopoly of his invention; the essential right of the inventor was thus lost sight of in the appearance of privilege-and the error has not been entirely discarded to this day. The almost annual attempts at amending the patent laws are only so

many trials to make the theory of privi lege, and its consequent practice, fit the universal feeling of right; but the crooked billet offers no face that will fit.

$

From this theory of privilege arises the necessity of affixing the signature of his Majesty to Letters Patent; and to obviate the inconvenience of delay in ob. taining it, the Bill proposes to substitute temporarily the signature of one of the Chief Justices; but if the granting of a patent be not the conferring of a privi lege, but the defining and registering of a right, what need is there of the signature of his Majesty, or his Majesty's substitute at all, more than to a thousand other do. cuments? The authentication of the record, under proper regulations, by a competent public officer appointed for that business, would answer the purpose far more effectually, more cheaply, and with much less irregularity and delay.

The cumbrous machinery by which the present law is worked, is not further affected by the Bill. But to what purpose can it be, that patents for inventions are submitted to the Attorney-General ? -a gentleman of a class, perhaps, of all others disqualified by the nature of their studies from judging of their merits,an officer, perhaps, of all others unable, from the multiplicity and importance of his engagements, and his uncertain tenure of office, to give them the necessary attention. It is easy to see how this practice has arisen out of the aforesaid theory f privilege; but is it not equally clear that, to do the needful justice, patents for inventions must be separated from other patents, and a separate department established for their supervision ? Ought not the whole property in inven tion, whether in literature, in science, in the fine arts, or in manufactures, to be placed under the protection of a separate tribunal, constituted with a view to this special duty?

In his zeal for the interests of patentees, Mr. Mackinnon seems to have forgotten that there are other parties who have rights too, or he surely could not have proposed the 8th and following clauses, by which, under a Judge's warrant, granted on an ex-parte bearing to a suspecting patentee, any designated workshop, &c. may be searched for infringements. Now wherever any inven tion is in progress, in customary privacy, there are always abundant and usually

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very inaccurate reports of its purpose; and however different the real object of the inventor, it is certainly never difficult to muster circumstances enough to coun tenance a suspicion that piracy is intended. But is it not a monstrous injustice to the new inventor, that his workshops should be ransacked and his plans exposed upon a real or pretended suspicion of piracy? and all this without warning, without opportunity of disprov ing the suspicion, without guarantee of secrecy, without right of action, without limitation, without remedy? It certainly would not be difficult to find those, who having bought up most of the patents in a manufacture, would be in condition, as soon as this Bill has passed, to rummage the workshops of half the trade. As for remedy by action at law, what is that to a needy, struggling, though clever, inventor, especially if opposed, as he probably would be, to the Leviathan of his trade? A little inquiry into the usual progress and actual state of any of our great manufactures, would convince Mr. Mackinnon that in its present form this part of his plan would work most grievous wrong.

While piracy of an invention is undoubtedly robbery, and ought to be pursued, whether by search or otherwise, with the same vigour as theft, there is an important difference to be noted between the search for stolen goods and that for infringement. In the former case, if property is carried away under pretence of search, the fact is easily proved, and redress readily obtained,the restoration of the goods sets the main matter right; but in the latter the property, consisting merely in the knowledge of the processes carried on, may be, and in most cases would be, stolen by means of this search obtained on suspicion, and carried away and used without redress to the robbed inventor, and not unfrequently to the barring of his just patent right-things cannot be placed on their former footing. Before Mr. Mackinnon procures the passing of these clauses, he ought, by every consideration of justice, to devise some mode of preventing this abuse: no subsequent remedy can apply. Let him do so, and then the search he proposes is but a righteous hunting out of thieves and receivers. More, perhaps, is to be expected from the inculcation of the maxim,

that he who infringes is a thief, and ought to be scorned as such, than from any positive enactment, useful as it may be.

The most novel feature of the new Bill is a proposal to establish a register for designs; the property in which is thus to be secured for twelve months on payment of ten pounds. This may be a step to wards something better; but a protection. for twelve months! and a tee of ten pounds Of what utility can so chargeable a regulation for so short a protection be to the manufacturer of stoves, of stamped brass goods, of cottons, of lace, of shawls, or of any thing made by wholesale? His patterns are indeed now stolen from him in the face of day; and whatever may have been the cost or talent by which they have been produced, some unscrupulous neighbour impudently appropriates the profits. Need enough: is there, of remedy to wrong, and impolicy like this, as the evidence already given in your pages amply testifies, and Mr. Mackinnon deserves thanks for even attempting to root out this crying injustice. But of all the designs offered to the public, many fail, and the manufac turer frequently cannot tell beforehand which will hit the public taste and which will not; yet he must register all, and pay upon all, or he robbed of those, and those only, which succeed. Few manufacturers, if any, can stand an expense like this; to them it will be useless in its present form, though it may be of ad vantage to the higher arts; and if it do not entirely break down from its obvious failure in practice at first (which is far from impossible), it may prove the imperfect beginning of a better system.

Sufficient attention has not, I conceive, been paid to the principle by which the duration of patents ought to be regulated. In cases where there is no possibility of the same thing being done over again independently by another person (as, for instance, the writing of a book), there seems to be justice, and therefore good, policy (for justice is always conducive. of good policy in the long run), in making the proprietorship perpetual. But the period should be shortened in propor tion to the probability of independent reproduction by others. There might be soune difficulty in applying the principle accurately to every case; but surely some approximation may be devised