applied, with success, to engraving in relief, and the medallion head of the Queen in that beautiful specimen of typography the Golden Sun, was executed by Mr. Freebairn with Mr. Bate's apparatus. That the relief must be good is evidenced by the immense number which has been issued of that publication.

In steel engraving, by the machine, two beautiful works have lately been published, one the bas-relief design from a salver, by the celebrated Jean Gougou, and the other a head of the Duke of Wellington. Gougou's salver, of which the engraving is a fac-simile, is nineteen inches in diameter, and one of the most elaborate and beautiful specimens of the art of metal-chasing, executed at a period when that art was practised to a far greater extent than in the present day, and by none more successfully than Jean Gougou. The design is divided into several compartments, containing groups of figures, emblematical of the four quarters of the globe, their principal conquerors, and the four seasons; the intermediate spaces being filled up with exquisitelyfinished ornaments of the style which prevailed in the 16th century, the era in which Jean Gougou flourished. Freebairn's engraving is the most clear, distinct, and brilliant representation of this rare work imaginable; the effect of the relief is beautifully deceptive, and is heightened by the metallic colour of the ink in which the engraving is printed; the most minute details are given with perfect accuracy, and the drawing, both of the figures and ornaments, is preserved with a fidelity that reflects the highest credit on the skill of the artist, and the accurate working of the machine.

Mr.

MR. NUTTALL'S MODE OF ENGRAVING IN RELIEF.

Sir,-In your Number for the 7th of July, you have inserted an abstract of Mr. Woone's patent for what he calls a new method of engraving. Now it happens, that the very same system was practised by myself upwards of five years ago; but I found the plan did not answer for the purposes of shading, or designing minute objects; nor do I believe that it can ever be made to answer, not only on account of the difficulty of drawing fine lines and shades on the composition Mr. Woone recommends, but also the utter impossibility of producing perfect

casts on metallic substances, as any caster of stereotype plates will inform him; for the moment his composition, mould is subjected to the heat of the furnace, it will crack, and fly from the body to which it was attached, whether wood, stone, or iron. Attempts at the above, however, eventually led to another mode of engraving, by which I have been enabled to produce fac-similes of shaded designs, maps, plans, &c.; some of which have appeared in the Gentleman's Diary, Gentleman's Magazine, Archeologia, and other works, with which I happened to be editorially or typographically connected.

At this time, I only want the cooperation of a skilful and confidential artist, not being one myself, to bring the invention into full operation. As to a patent, I am convinced, it would be no protection; and therefore, secrecy alone likely to secure any future advantage. The inclosed are two roughly printed specimens.

Yours, &c.

P. NUTTALL.

1, Gough-square, July 16, 1838.

[The specimens sent us by Mr. Nuttall, consist of a view of an ancient gateway, and a head of Virgil, under which is printed the following note, "This HEAD OF VIRGIL, as being the first rude specimen of a new chemico-mechanical Bucolics, and executed without the agency art, invented by the editor of these of wood, stone, or metal of any kind, is given as a curious graphic novelty. Thus, from a simple drawing myriads of copies may be produced with almost the same ease and certainty as common letterpress printing." The specimens prově that Mr. N.'s plan is one capable of being carried to great beauty of execution, in experienced hands; the relief appears from the indentation upon the paper impressed, to be considerable-and the lines are fine, and clear. As we mentioned of Mr. Woone's plan, however, the object to be obtained is not beauty, but rapidity of execution.-ED. M. M.]

his mercurial pump. (vide page 231.) As "Nautilus" very justly observes, in your last Number, I certainly did make a "most extraordinary blunder," in calling that machine a lifting force-pump; it is in reality a force-pump.

By common consent it has become the practice to divide pumps generally into three classes, viz., the common suctionpump, the force-pump, and the lifting force-pump. The first class are distinguished by a valved piston working in an open-topped cylinder; the second class have a solid piston; while the third description have a valved piston working in a close-topped cylinder, the piston rod moving through a stuffing box, and thereby converting the machine into a forcing-pump to any extent in the lift.

It

Most of the pumps in common use are readily assigned to one or other of these classes; but, among the philosophical toys of the lecture-table nondescripts are of frequent occurrence. should be borne in mind, that by far the greater number of pumps depend for their first action upon suction (I am quite content to use this expressive and well-understood term in the absence of a better), and it is only after the barrel has been filled by suction that the ресиliar office commences which fixes the character of the pump, and assigns it to one of the three classes enumerated above. The term common suction pump," is exclusively applied to the simplest form of pump, having one valve in the piston and another at the bottom of the working barrel, and only capable of raising water to the top of its own barrel.

66

Although I have sadly blundered, I think "Nautilus" will see that, after all, my mistake will not afford a peg for Mr. Mills to hang a rejoinder uponespecially after the dressing he has received at the hands of our lynx-eyed friend.

I remain, Sir, yours respectfully,
WM. BADDELEY.

London, July 31, 1838.

OBSERVATIONS ON DUTY AND HORSE

POWER.BY J. S. ENYS. ESQ.

(From the Cornwall Polytechnic Society's Report.) The origin of the term duty in Cornwall, -and horse power in the rest of the kingdom, may be readily traced to the different circumstances under which Watt's low pressure engine was introduced, and the dif

•ferent nature of his agreement with the miner, and manufacturer. The former was in possession of a powerful but expensive machine, by whose means a new era of mining had been commenced, and the reduction of the coal expenditure was his object; while the latter was in want of means of entering into competition with water power, and of rendering the coal itself, and the fertile districts in which it is often found, available for manufacturing purposes.

In several of the deepest Cornish mines of that period, the exertions of the adventurers were paralysed, since the water charge approximated to, or even exceeded the returns of ore, while favorable mining symptoms urged on an extended trial. The characteristic caution of miners in the introduction of new machinery on property, whose value was not above two or three years' purchase, is apparent, in the agreement that Watt should receive one-third of the savings accruing in the performance of an equal amount of work by his engine in comparison with Newcomen's. The range of load of the latter engine, is nearly as great as in Watt's low pressure engine; and in both the number of strokes per minute are regulated by the same means, and it remained in nearly general use in coal mines until after the expiration of Watt's patent, and even then the most essential parts of the patent-the air pump, and condensing pipe for the injection water-were often added to old engines of Newcomen's construction.

The atmospheric engine thus improved, would not be much inferior to Watt's engines, when worked at full pressure, in the performance of mining duty, if equally well constructed. The determination of Messrs. Boulton and Watts, to force their steam pressure engine into use, instead of consent ing to receive a share of the savings of coal, on a similar agreement for the application of the air pumps and condensing pipes to the old atmospheric engines, caused a large outlay of capital in Cornwall, from the necessity of taking these engines, at first, at prices far above their value, and of erecting the patent engine at a moderate charge, with a view to repayment, by the annual payments of the coal savings; with the exception, that these savings might be redeemed at ten years' purchase, Watt steadily adhered to the terms originally proposed, which proved exceedingly favorable to the patentees, in as much as the duty due to improvements in the pitwork and boilers, which were equally applicable to Newcomen's engines, more than counterbalanced the disadvantage in many shafts, which was unavoidably caused by their increase of depth, arising from the lessened coal expenditure, the patentees are supposed to have received nearly £180,000,

exclusive of the profits of erecting engines during the latter years of their patent.

In 1781, three years after these arrangements, Hornblower, a descendant of one of the engineers brought into Cornwall by Newcomen, took out a patent for the double cylinder engine, to work steam expansively; and in the ensuing year, Boulton and Watt's second patent appeared for a similar application of steam in a single cylinder, together with six patent contrivances for equalising its effect. This patent included the double acting engine, a contrivance which by lightening the fly-wheel, and from its compactness and double power in the same space, facilitated the introduction of the steam engine for manufacturing purposes. It also seemed a favorite with its inventor for mines, though now totally abandoned, as it either requires a balance, or a double column of pumps in the shaft, and hence increased friction, with a double chance of stoppages from accidents. By means of double action, however, a considerably greater power was obtained by a double acting 63-inch cylinder, than had been before afforded by a 72-inch atmospheric engine, which was necessarily single acting. Probably Messrs. Boulton and Watt had not tools capable of boring cylinders larger than 63-inches in diameter, with sufficient accuracy-at least, they never ventured to erect any of a larger size; and even then, only single actingthough after 1800double acting 63's were used.

Expansion in the last fourth part of the stroke, and even to a greater extent with a light load, was soon used by Watt in pumping engines, often as much to guard against too great an acceleration of the piston towards the end of the stroke-from the reduced resistances of the pitwork, as soon as its inertia, and that of the water in the bucket pumps of that period, had been overcome by the constant steam pressure-as for economy of fuel.

The requisite conditions for the coincidence of the practical and theoretical advantage of the expansive action of steam, were not ascertained until a more recent period, when high steam was used expansively, to produce a mean pressure equivalent to, and often exceeding, that of steam of 2lbs. above atmospheric strength, used at full pressure. After a sharp contest of about fifteen years, during which Watt's counter was again used to decide on the relative performances, by registering the number of strokes made per bushel of coal, between Woolf, in a double cylinder engine, and the other mining engineers, in Watt's engine, assisted by Trevithick's cylindrical boilers, -all using high steam expansively-a preference has been given to the single cylinder

engines, which are now alone used in Cornwall for pumping. Woolf himself was often obliged by the managers of mines, to erect single engines; and the engine bearing his name at Consols, took a leading place in the performance of a duty above 60 millions, but was soon excelled by Wilson's engine at Wheal Towan.

During a period of 70 years, the method of estimating the work performed by the load in the shaft, and by the space through which it is lifted by the steam produced during the average time of the consumption of each bushel of coal, has been in constant use, the result is an expression in lbs. lifted one foot high, which was termed by Watt, the duty of the engine.

The recent act of parliament for the substitution of the imperial bushel (94lbs.) instead of the Winchester of 90lbs, both weighed damp from open yards, has caused a change that should not be neglected-and Watt's duty of 27 millions in the Cornish mines, must be increased to about 30 millions.

The manufacturer is unable by equivalent methods to ascertain the work performed in lbs. one foot high, and moreover his object was a moving power within certain limits of expense, which would afford him a choice of situation free from winter floods-or deficient power in summer, and capable of unlimited extension.

The obvious basis for the supply of such power, was that which could be exerted by a horse, and this had been estimated from actual work in pumping water,-exclusive of friction, &c., &c., by Smeaton, at 22,000 lbs. one foot high,-and by other persons at a higher rate,-but whether exclusive or inclusive of machinery or pitwork resistances, (a point too much neglected in technical terms at least,) is not quite clear.

To prevent disputes on this point, Watt seems to have added one half to Smeaton's estimate of horse power, and fixed the surplus steam pressure,-which should be considered equal to a horse power, after engine resistances were deducted, at 33,000lbs. one foot high, which is equal to a steady draught of 150lbs. like a weight over a pulley, for 8 hours, at 2 miles per hour.*

The power of a horse is always partly expended in overcoming the resistances of the machinery necessary for its conversion into the pressure and velocity required, and even in the simplest case, the weight of the waggon employed in the conveyance of goods.

*The nomical HP. of engines has been sometimes x by 3 for the relays of Horses requisite for constant work during 24 hours-and again by 1. to allow for the inferiority of Cornish horses, by this process, mining engines of 200 HP- have been called 900 HP.

The essential distinction of duty is, that it is founded on the load either actual, or calculated exclusive of such resistances.

When these are included, the power to produce motion being always one of them, to reduce it to a aimple statical question, the term effect would prevent confusion, and it would be equal to the H.P., as measured by the surplus or effective steam pressure, after the engine resistances are deducted, by the space of action of the piston per minute.

In mining engines, the duty has always been calculated from the weight of a column of water, equal in diameter to the working part of the pumps, without any allowances for short strokes and other causes, and the practice seems occasionally to have been adopted, of considering the resistances of the pitwork balanced by the deficiency of the actual, in comparison with the calculated delivery of water,-in which case, by substituting the space passed over per minute, instead of the space per bushel of coal-the effect the H.P. of the engine will be obtained in lbs. one foot high from the calculated load for duty. Suppose [for example, that Davey's engine, an 80-inch cylinder, Consols, makes 400 strokes, and consumes 4 bushels of coal per hour, a close approximation to the facts- the space of motion in the shaft is 583 feet per minute,-and 875 feet per bushel of coal-the pump stroke being 8 feet.

Effect H.P. 5S = 4,87925 = 148 875 74.827750 Duty, per hour.

or 2.54lbs. of coal per H.P.

In consequence of greater attention to the full length of the strokes, and the improved state of the pitwork, the deficiency of water delivery is less than at any former period,the friction has been greatly decreased, where main and pump rods are of equal lengths, but the depth of many shafts have been nearly trebled, since Watt's engines were first erected. Possibly the following estimate of the effect, H.P., in deep shafts, will be a fairer approximation than the first method. Davey's engine works in a shaft 290 fathoms deep from the surface, in which about 300 tons are put into motion at each stroke, though all, except the load, is balanced

Calculated load 85.530lbs.

Deficiency.. 10.691 from various causes.

It is obvious that the denomination of the units of which, duty is composed, may be changed at pleasure, and that either of them may be made the varying quantity: thus a duty of 70.000.000, the average of the 12 or 13 best engines reported, may be expressed, as a bushel of coal (94lbs.) lifting its neighhour 146 miles high-and the largest known moveable unit,-an 120 gun ship, fully equipped, if left by the tide, would be lifted off the beach, 7 feet high, by a bushel of coal.

In the railroad form, which is strictly a duty, though the term does not seem to be yet applied, it becomes, on the supposition that 1 ton is equal to 8lbs. over a pulley-1 ton, 1 mile per 057lbs. of coal-in such estimates the weight of the locomotive engine should be taken as part of the neat load, and under such circumstances, if the duty was 1 ton, 1 mile, per 1lb. of coal, it would be expressed in the Cornish method by 3.969-560lbs. one foot high, or just four millions duty.

As the importance of the economy of fuel became felt in manufactories, the comparative estimate of the quantity expended, was commenced in the form of lbs. of coal per H.P., per hour; a method well known, from its general application to steam boats-but neither this, or any expression derived from this source, such as the number of miles 1 ton of coal will impel 1-horse power-ought to be termed a duty; at least, if an usage of more than 60 years can give any claim to the use of the technical word, with a defined meaning.

The load for duty would be the draught in lbs. due to the area of the midship section, with the given stern and bow angles.

The load for effect, would be the pressure due to the area and number of the paddles x by the difference of the squares of the velocities of the wheel and vessel + the friction of the levers and the shaft-the difficulty of ascertaining these points, which would be very great in smooth water, and which would be much enhanced in rough weather, has probably led to the adoption of the nominal H.P., as an unit in the comparative estimate of the fuel expended—the H.P. exerted would afford a better test-since the former is obtained from an estimated surplus steam pressure on the piston, notoriously less than that which is exerted in modern engines x by the space of action of the piston, which is taken at from 200 to 220 feet per minute.

In fine weather, these engines are generally worked from the above cause, at one fourth more than their nominal horse power, and this difference is greater whenever