I do not doubt experiments with such a generatrix would be most unsatisfactory, and it frequently happens that experiments give far different results from what was anticipated, owing to disarrangements not always fully understood.

As this is a subject of some interest, we will consider it practically. To any who feel disposed to satisfy themselves of the utility of a centripetal propeller, I will furnish one of any size, at the same rate as a common propeller; and if it does not fully answer, will refund the money. Philadelphia, July 22d, 1851.

Interesting and Unprecedented Test of Chains and Iron Rods.*

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J. Foster, Esq., and the Rev. J. B. Owen, of Bilston, G. R. Hickman, Esq., of Tipton, and several other gentlemen interested in scientific experiments, attended at the cable manufactory of Mr. H. P. Parkes, Dudley, to witness some extraordinary tests of the strength and toughness of iron used in the fabrication of chains. When any one considers the frightful loss of life so frequently the result of the breaking of a single link in a chain, or the failure of a girder in an iron roof, the importance of any decided improvement in the metal and workmanship employed for such purposes cannot be too highly appreciated. Several samples of round chains, of § of an inch size, were put to the hydraulic proof, and whereas the interstices between the links, previous to their tension, measured only the of an inch, after proof it had stretched equally, even without loss of symmetry in shape, to 18 inch. One of these pieces of inch chain sustained without a flaw, 18-10 tons, being nearly four times the ordinary testing weight. It is due to the enterprising and intelligent experimentalist, Mr. Millington, of the firm of Messrs. W. Millington and Co., Summerhill Iron Works, Tipton, to state that of all the qualities of iron submitted to the proof, the material furnished from his works stood the severest test. Its fabric is a novelty to the trade, and will be shortly patented. Mr. Parkes has contributed a sample board of chain to the Great Exhibition, in sizes varying from 1 to 2 inches, which have been tested by unprecedented proof, at his factory at Tipton. This series of experiments, probably of some importance to the Staffordshire trade, terminated, not unnaturally, with the tying-in iron of "the Staffordshire Knot." A piece of inch round of Mr. Millington's iron, formed into a nose at each end, and gracefully formed into a loose tie, was drawn in cold metal into a tight compact knot, lifting in the process the unparalleled weight of 8 tons. The chains seemed elastic as gutta percha, and stretched to nearly double their length during the proof, and like metal paralyzed, became rigid, and straight as an iron bar.

Convolute Boiler.-Registered for MESSRS. GARTON & JARVIS, Exeter.† This boiler is intended for heated conservatories or public buildings by steam, or the circulation of hot water. Our engraving represents the boiler in perspective, with the fire-doors removed. The boiler, A, is of

*From the London Mining Journal, No. 822.

From the Glasgow Practical Mechanic's Journal, June, 1851.

the convolute form, having the grate-bars, B, within it. It is made either of wrought or cast iron, or copper, the water space between the two parallel sheets of metal forming the volute, being three inches in breadth. The course of the draft is very obvious; it passes from the

interior of the convolute out by the open overlap, and then completely round the exterior of the boiler, which is surrounded by brick-work to form the external flue. The pipe, C, forms the water communication between the body of the boiler and the crown. The heated current of

water flows off to the locality to be warmed, by the pipe, D, and the heavier cooled water returns by the bottom pipe, E. It will be seen that the peculiar feature of this arrangement, is the effective mode in which the entire internal and external surfaces are exposed to the action of the heat. Several boilers on this principle are in the exhibition.

FRANKLIN INSTITUTE.

Proceedings of the Stated Monthly Meeting, July 17, 1851.

S. V. Merrick, President, in the chair.
Isaac B. Garrigues, Recording Secretary.

The minutes of the last meeting were read and approved.

Donations were received from The Royal Astronomical Society, London; The Smithsonian Institute, and R. P. Anderson, Esq., Washington City, D. C.; Simeon Borden, Esq., Fall River, Massachussetts; Jordan L. Mott, Esq., City of New York; S. H. Palairet, Esq., George Harding, Esq., Charles E. Smith, Esq. and the Pennsylvania Railroad Company, Philadelphia.

The Periodicals received in exchange for the Journal of the Institute were laid on the table.

The Treasurer's statement of the receipts and payments for the month of June was read.

The Board of Managers and the Standing Committees reported their minutes.

The Board of Managers reported that at their last meeting they re-appointed Mrs. Sarah Peter, Mrs. S. V. Merrick, Miss Ellen Lawson, and Messrs. S. V. Merrick, D. S. Brown, and Frederick Fraley, the Committee on the School of Design for Women, for the ensuing year.

New candidates for membership in the Institute (3) were proposed, and the candidate proposed at the last meeting was duly elected.

Mr. Walcott, of Boston, exhibited Robinson's back-stitch sewing machine, in operation before the meeting, which excited much admiration from the members present, and made the following remarks:

This useful machine was patented in December, 1850. The object of the invention is to produce either what is generally termed, stitch and back stitch sewing or ordinary stitching, but this machine not only sews the regular back stitch, but with slight mechanical adjustment, the basting, whipping, quilting, and cordwainers. There is a combination of two needles, two thread guides, and a cloth-holder, made to operate together, each needle having a spring to which pressureis applied in passing through, which spring retains the thread. The whole is worked by a wheel which governs and regulates the motion, with a handle on the wheel, which could be turned by a child; the whole apparatus showing great mechanical skill and ingenuity.

The advantages claimed for this machine over all others, are the durability and the fastness of the stitch; the perfect simplicity and compactness of machinery, and the many purposes to which it can be applied. The stitch taken by this machine is a fac simile of hand sewing, consequently it can be successfully applied to the same purposes. It also possesses many advantages even over hand sewing, which the practical tailor admits. The sewing produced is more accurate, makes a firmer seam, and is more durable than that done by hand. In hand sewing, at intervals of stitches, the thread remains loose, and therefore, allows the stitch taken to slack, which we overcome by keeping the thread continually tight by means of thread holders, which act in the capacity of fingers.

In seaming clothing with silk, it is very necessary that the silk should be waxed to give a firm seam. It is well known that all kinds of silk will stretch about one inch in ten. This machine will work the silk waxed, as well as without.

An interesting relic in the form of a musket was presented to the Institute by Jordan L. Mott, Esq., of New York, obtained from the wreck of the British Frigate Hussar, which was sunk in about 75 feet water, 1 miles from Hurl Gate, East River, Nov. 14th, 1780. The brass was in the most perfect state of preservation, whilst the barrel, lock and screws, were reduced to the state of oxide.

JOURNAL

OF

THE FRANKLIN INSTITUTE

OF THE STATE OF PENNSYLVANIA

FOR THE

PROMOTION OF THE MECHANIC ARTS.

SEPTEMBER, 1851.

CIVIL ENGINEERING.

On the Nominal Horse Power of Steam Engines. By COMMANDER L. G. HEATH, R. N.*

The inadequacy of the present term "nominal horse power" for giving a definite idea of either the absolute or relative power of engines was first examined, by comparing the engines of H. M. steamships Garland and Basilisk, which were both constructed on the same principle, with oscillating cylinders, and were both used to drive paddle wheels. This comparison was made under three distinct heads,-the mean effective pressure, the number of revolutions per minute, and the size of the cylinders. It was urged that Watt's constant of seven pounds per square inch, for the mean effective pressure, was not only in itself inapplicable, but that no constant quantity could be universally applicable. Also, that the method of determining the number of revolutions per minute, from a conventional speed, founded on the length of stroke of the piston, was equally fallacious. It was therefore proposed, that the term "nominal horse power" should be abolished; and that engines should in future be designated by the cubic contents of their steam cylinders, jointly with their nominal consumption of a standard description of fuel during a given period of one hour. A table might be drawn up giving this nominal consumption in terms of the grate and the heating surface, and should be accompanied by rules and directions for ensuring the uniform measurement of the grate and the heating surface. This system, it was contended, would be more in accordance with the present practice of construction, and would enable the relative size and power of engines to be more accurately estimated than by the present method.-Proc, Insti. Civ. Eng., April 8, 1851.

From the London Athenæum, April 9, 1851.

VOL. XXII.-THIRD SERIES.-No. 3.-SEPTEMBER, 1851.

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It was admitted that it would be very desirable to fix the nomenclature of the power of engines; for though it was well known that James Watt did really take as his standard, what he found to be actually performed by a powerful horse drawing a weight over a pulley,-viz: the equivalent of 33,000 lbs. raised one foot high in a minute-yet commercially it had gradually become a custom among the manufacturers to give a surplus of power, ostensibly as an allowance for the friction and deficiencies of the machine, so that now, the mere statement of the nominal horse power had no definite meaning. It was, however, contended that the standard of 33,000 lbs. should be retained; and that, supposing the workmanship to be equally good in two engines, it was only necessary to compare the areas of the cylinders, the effective pressure of steam on the piston, and the speed of the piston, to determine their relative power. This was, in fact, shown by the indicator, an instrument the value of which was now universally admitted, and which, when skilfully used, did really give a true representation of the power of the engine. It was the universal custom of Boulton and Watt to calculate the power exerted by an engine by the speed of the piston, together with the average pressure of the steam, as shown by the indicator; and although much vagueness and uncertainty had latterly been introduced into the subject, this was rather to be attributed to the assumption of arbitrary quantities to represent those results, than to any defect in Watt's standard horse-power, which definitely expressed both the measure of power and the space through which it acted. The proposed standard of comparison of the quantity of water evaporated in a given time, by a given amount of fuel, or the combustion of a given quantity of fuel in a given time, were shown to be of no value; as then not only the generation of the steam, but the administration of it, must be considered, and these were points merely tending to complicate the question. For pumping engines in Cornwall, the term horse-power, was almost unknown, engines being sold to raise a given quantity of water, which was a standard easily reducible to that of other districts, where 33,000 lbs. was assumed to be the actual power of a horse.-Proc. Inst. Civ. Eng., April 15, 1851.

For the Journal of the Franklin Institute.

A New Method of Calculating the Cubic Contents of Excavations and Embankments.-BY JOHN C. TRAUTWINE, C. E.

Entered, according to the Act of Congress, in the year 1851, by JOHN C. TRAUTWINE, in the Clerk's Office of the District Court of the United States, for the Eastern District of Pennsylvania.

Continued from page 88.

In the following tables of level cuttings, the left hand vertical column contains the height or depth of the embankment or excavation, in feet; and the upper horizontal column, the intermediate tenths of a foot. Thus in table 1, the cubic yards in a station 100 feet long and 10 feet deep, are 1074; for 10-1 deep, 1090; for 10-2 deep, 1107, &c.