"Figs. 1 and 2 represent a paddle-wheel of a steam-vessel, constructed in the ordinary manner, except only as regards the floats, a a a a: instead of these floats being placed parallel to the shaft or axis B, as such floats are now usually placed, they are fixed obliquely, at a considerable angle thereto, and in alternate opposition to one another, as shown in the drawing, each float projecting beyond that opposite to it. By placing the floats in these relative positions, the amount of direct resistance from the water, and of propulsive power thereby obtained, is greater than is obtainable within the same width of space, by any other arrangement of floats with which I am acquainted, while at the same time the power is exerted unintermittingly and continuously throughout each entire revolution of the wheel, and acts in an equable and steady manner on the vessel and its machinery. In consequence, too, of the oblique direction in which the floats enter into and emerge from the water, as well as of the water being drawn, as it were, into the interior of the wheel, between the floats, there is less of that back lift and dashing of the water against the sides of the vessel, which are so much complained of, and are so peculiarly objectionable in canal and river navigation."

Instead of one set of floats, placed in alternate opposition to one another, as represented in figs. 1 and 8, the patentee states that two or more sets may be placed side by side, in the manner shown in fig. 2.

We see no reason to question that a paddle-wheel, with floats set in the manner invented by the patentee, will be greatly superior to the common wheel. All the schemes which have been hitherto proposed for the improvement of the common wheel, appear to have only served to produce a wider-spread conviction than ever among practical men, that no wheels are so well adapted to the rough work to which steam-vessels are exposed-ocean steamers especially-as those which have fixed and well-secured floats. Mr. Chatterton does not quarrel

with this conviction; but contends, only, that fixed floats may be fixed at such angles with respect to the plane of motion and to one another, as to realize nearly all the advantages predicated of the various feathering paddle-wheels which have at different times been brought before the public. He states what he thinks are the best angles for the purpose, (" but without confining himself to these precise angles,") and gives reasons for preferring them, the soundness of which will, we think, be very generally admitted. We beg, however, not to be understood as looking on the feathering system as one to be abandoned in utter despair-thinking, on the contrary, well of it, and hoping still to see it produce good fruit. All we mean to say is, that, so far as the most approved practice of the present day goes, the paddle-wheel of Mr. Chatterton is step in advance, and one which, though in an oblique, is nevertheless quite in the right direction.

The plan of Mr. Chatterton has, we understand, been already adopted with acknowledged advantage in Canada, (the birth-place of the invention;) and it is now in course of application to one of the vessels of the St. George's Steampacket Company, which will soon afford the British public an opportunity of judging of its merits, from ocular demonstration.

THE CASE IN LIFE ASSURANCE-MR.
SCOTT IN CONTINUATION.

Sir,-Having in my last communication promised to give another solution of Iver M'Iver's Question on Life Annuities deduced from more healthy_tables than those of Northampton, I have made out the following calculations from the duration of life given by Mr. Muret in the first part of the Berne Memoirs. It will be found that the Swiss Table of Mortality agrees very nearly with the Carlisle Table of the Duration of Life; the mortality between the ages of 23 and 43 by the Swiss Table being expressed by the decimal 1828, and the Carlisle by 1833. The number living by the Swiss Table, at the age of 23 is 597; at 24, 592, &c., and at 43, 488;

over the thermometer conductor bar, I am not prepared entirely to dispense with the latter. Inferior, certainly, as it is to Mr. Houldsworth's pyrometer in the rapidity and correctness with which it indicates the fluctuations of temperature in the flues of a boiler, it has nevertheless great advantages as a permanent indicator of the maximum and minimum ranges of such temperature; from which the engineer soon learns to form a series of valuable inferences as regards the state of the flues,-the general action of the furnace, and, above all, the heat-generating faculty of any kind of coal, or mode of effecting its combustion.

Independently, however, of the practical value of Mr. Houldsworth's wire pyrometer, I hail its introduction as of the last importance at this particular period, when the subject of the "smoke nuisance" has engaged so much attention, and when so many are desirous of being set right, not only as to the means of abating that nuisance, but as to testing the relative value or applicability of the several kinds of furnaces which are daily presented to their notice. On turning my attention to this subject some few years back, as a matter of business, and desirous of comparing the several "smokeburning" and fuel economizing plans, no other test presented itself or was even thought of, but that of evaporation. I was perplexed, however, by the prevailing uncertainty and total absence of principle or system, even among our most eminent Mechanical Engineers. No scientific or satisfactory reason was given for preferring one description of furnace or boiler to another and as to practical results, matters were still more inconclusive. The application of one kind of furnace, which was found to succeed with one class of boilers, was wholly unsuccessful when applied to another class. Each Engineer had his own, pro tempore mode of calculation and construction, as regards boilers: yet these were ever changing, and still are as far as ever from either certainty or perfection.

When, again, I looked to writers on the subject, I found still less reason to be satisfied. With them, all that regarded either the furnace or the boiler, and all the details of ash-pit, fire-bars, flues, and even areas for the admission, escape, or draught of air, were at once reduced to a question of proportions-mere mechani

cal proportions, unaccompanied by any chemical or scientific reason. With all these endless varieties of furnaces and boilers and proportions, the sole comparative test of efficiency was evaporation— the weight of water evaporated by a given weight of fuel. That this was not only a fallacious but deceptive and dangerous test, was manifest from the fact, that the same description of furnace and fuel was attended by a large measure of evaporation when applied to one plan of boiler, and the reverse when applied to another. It was clear that there was something radically wrong in our mode of proceeding. Two things were manifest, first, that the relative value of the processes of combustion as they occur in different kinds of furnaces, with their purely chemical combinations and effects, must be tested by some other means than by mere reference to the secondary process of evaporation in boilers: and, secondly, that a knowledge of the principles on which furnaces and boilers should be constructed, with reference to their respective but very different functions, must be sought for in some more rational and scientific course of proceeding, than by a mere calculation of sizes and surfaces, mechanically considered. In a word, that the branch of science which treats of the generation of heat, by combustion, from fuel, must be separated in our experiments, as well as in our minds, from that of the generation of steam by evaporation from water— two objects which have nevertheless hitherto been so unaccountably and unscientifically compounded, and have so long prevented our obtaining correct or systematic results as to either.

In illustration of the vagueness which attends all experiments where this confusion prevails, I have arranged in the form of Tables, the results of nine experiments made under my own eye, together with others which have been most relied on by Mr. Parkes and Mr. Wicksteed. These Tables I submitted to the mechanical section of the British Association at Manchester, in consequence of the interest taken in that town on the "smoke nuisance" prevention. I now submit them to your readers with the same object,— the showing how liable we are to be deceived by results and inferences drawn from these two popular modes of proceeding, namely, the constructing boilers

and furnaces by empirical rules drawn from a calculation of mere mechanical sizes and surfaces: and the testing the heat-generative properties of a furnace by the evaporative powers of a boiler.

On both these points these Tables are decisive, in proving the utter fallacy of the inferences hitherto drawn, and the absence of all system, or the means of correct calculations as regards either the size of the furnace, the surfaces of the boiler, the fuel used, or the water evaporated.

Among those practical men who had hitherto looked to the measure of evaporation as the test of relative merit in the various "smoke-burning" systems, none has given more attention to the subject than Mr. Houldsworth. In search of truth and practical effect, on the large scale, he has pursued the inquiry for years, and to him we are now indebted for the means of testing the heat-generative values of the various modes of producing combustion in furnaces, by direct reference to the actual amount of heat generated, rather than by the indirect process of evaporation, which can only indicate what portion of the heat has been applied. To the use of Mr. Houldsworth's wire pyrometer I will again revert, being engaged in a course of experiments on the subject. The Tables now submitted sufficiently demonstrate the little dependence that can be placed on evaporation as the means of ascertaining the value of any kind of furnace. They also show that, in the construction of either furnace or boiler, this eternal and exclusive reference to mere mechanical properties, sizes, and areas, is as unsound and inconclusive as it is unscientific. This latter subject I propose continuing in my next communication.

I am, Sir, yours, &c.,

C. W. WILLIAMS.

Liverpool, July 15, 1842. Conclusions deduced from the accompanying Tables.

1. That the quantity of water evaporated by any given weight of fuel, (as shown in column 10,) furnishes no test of the quantity evaporated in any given time, (as shown in column 9.)

2. That the quantity of water evaporated by each pound of coal is a very inadequate test of the quantity of heat given out by such coal, or the perfection of the process of combustion carried on

in the furnace and flues; inasmuch as the steam generated is only in proportion to the heat taken up by the water, and not to the heat generated from the coal.

3. That, as the weight of water evaporated per pound of coal bears no proportion to the weight of water evaporated per hour, economy of fuel may, (according to the demands of the engine,) be the reverse of economy of time; and, as the work done may be estimated in proportion to the weight of water evaporated per hour, rather than the weight of fuel used, the latter can be no test of the former.

4. That the size or area of the furnace, or heating surface of the boiler, (as shown in columns 5 and 6,) has no necessary connexion with the heat-generating power of the coal, as shown in columns 9 and 11; (See Experiments Nos. 8 and 11, and Nos. 7 and 13.)the latter depending on the management and construction of the furnacethe quantity and mode of admitting air, and the rate of combustion, and not on any scale of proportions.

5. That the power of any description of coal should be tested by the quantity of heat produced:-the efficacy of any description of furnace, by the degree of perfection in which the process of combustion is carried on :-and the value of any kind of boiler, by the quantity of water evaporated. In experimenting with the first, (the coal,) we must be guided by the thermometer, or pyrometer; with the second, (the furnace,) by the eye, in observing the colour and character of the flame in the flue, and the absence from smoke; and with the third, (the boiler,) by the quantity of steam supplied to the engine in any given time. Each, however, should be tested by itself.

6. That, in estimating the effect produced by any kind of coal or description of furnace, (if a boiler be used,) we must take into account, not only the weight of water evaporated, but also the temperature of the escaping products, (as shown in column 11), the heat passing by the chimney being as well entitled to be considered as work done by the coal, as that which passes into the boiler doing the work of evaporation.

7. That the temperature of the products escaping by the chimney will be in the ratio of the heat in the flues, and both, in the ratio of the rate of combustion and the quantity of heat generated.

(Experiments arranged in the Order of Economy of Fuel used, as shown in Column 10.)

Showing that the Weight of Water Evaporated by each Pound Weight of Coal bears no Relation to that Evaporated per Hour; and, therefore, that what is called
Economy of Fuel may be a ruinous waste in Time and Work done by the Engine.