12

this hole he then filled with platina; the whole wire was then drawn until the entire diameter was no more than the both part of an inch; consequently, he had a wire of platina within the silver equal to the 30th part of an inch in diameter; and this he disengaged by immersing the whole in nitric acid, which precipitated the silver, and left the platina unaffected.

(To be continued.)

THE NAUTICAL ALMANAC. Sir,It was some time ago announced that government had been at length awakened to the necessity of rectifying the many blunders for which the Nautical Almanac has been long so disgracefully notorious. Will you give me leave to ask, through your medium, what it has been doing since it was awake? Who is the new Superintendent? Or, if we are to have a new board, who are the members? In your notices, Mr. Editor, on this subject, you overlooked what I thought to be a very piquant argument in favour of a reform. It is given by Mr. South in the form of a story, which goes thus: When Captain Smyth was employed in making a survey of the shores of the Mediterranean, he fell in with a Spanish frigate; an interchange of civilities took place, and Captain S., knowing how much the Nautical Almanac of England was, in former and better times, prized by foreign seamen, gave the Spanish captain all the volumes of it which he possessed. Fortunately, for the benefit of hydrography, Captain Smyth, with his foreign ephemerides, found his way to England; but there is an awkward story afloat, that the Spanish captain has not since been heard of. As Mr. South pithily adds, Quid est, si non hæc contumelia? I am, Sir, &c. ORION.

ASTRONOMICAL DISCOVERIES. The late Sir W. Herschell directed the attention of astronomers to the importance of determining the distances and positions of double and triple stars, or stars which appear single to the eye, or when seen through an inferior telescope, but when viewed with one of higher magnifying powers, are

found to consist of two or more distinct stars. Sir W. Herschell published descriptions and names of 702 such double and triple stars. Messrs. J. W. H. Herschell and Mr. South subsequently instituted a series of observations to determine the existence and amount of annual parallax of these stars; but this object was soon lost sight of amid the more extensive views of the construction of the universe which gradually unfolded themselves. These gentlemen have established the existence of binary systems, in which two stars perform to each other the offices of sun and planet. They have ascertained, with considerable exactness, the periods of rotation of more than one such pair. They have observed the immersions and emersions of stars behind each other, and have detected among them real motions sufficiently rapid to become measurable quantities in very short intervals of time.

CURRENTS OF THE OCEAN.

The following interesting observations on this subject were made by Captain Sabine, in the course of one of his recent scientific voyages :·

"In the voyage between Cape Mount and Cape Three Points, the Pheasant's progress appears to have been accelerated 180 miles by the current, which, in the season when the south-west winds prevail on this part of the coast of Western Africa, runs with considerable velocity in the direction of the land round Cape Palmas, to the eastern parts of the Gulf of Guinea. In the passage between the River Gaboon and Ascension, being a distance of 1400 geographical miles, the Pheasant was aided by the current above 300 miles in the direction of her course. But the more important distinction, both in amount and in utility in navigation, is between the waters of the equatorial and the Guinea currents. These exhibit the remarkable phenomenon of parallel streams, in contact with each other, flowing with great velocity in opposite directions, and having a difference of temperature amounting to ten or twelve degrees. Their course continues to run parallel to each other, and to the land, for above 1000 miles; and according as a vessel, wishing to proceed along the coast in either direction, is placed in the one or the other current, will her course be aided from

40 to 50 miles a-day, or retarded to the same amount. On the day after the Pheasant sailed from Maranham, she entered the current, the full strength of which she had quitted to go to that place, and it was then found to be running with the astonishing rapidity of 99 miles in 24 hours. On the 10th of September, at 10 A.M., while proceeding in the full strength of the current, exceeding four knots an hour, a sudden and very great discoloration of the water a-head was announced from the masthead; the ship being in 5° 08′ north latitude, and 50° 28′ west longitude, (both by observation,) it was evident that the discoloured water could be no other than the stream of the Amazons, pursuing its original impulse at no less than 300 miles from the mouth of the river, its waters not being yet mingled with those of the ocean, of greater specific gravity, on the surface of which it had pursued its course. It was running about 68 miles in 24 hours. On a general view of the currents which have been thus particularised, on the Pheasant's progress, in her voyage commencing at Sierra Leone and terminating at New York, it may be seen that she was indebted to their aid on the balance of the whole account, and in the direction of her course from port to port, not fewer than 1600 geographical miles, the whole distance being under 9000 miles; affording a very striking exemplification of the importance of a correct knowledge of the currents of the ocean to persons engaged in its navigation, and consequently of the value of the information

13

in the acquisition and arrangement of which Major Rennell has passed the later years of his most useful life. The publication of the charts of the currents in the most frequented parts of the ocean, which he has prepared with his accustomed and well-known indefatigable assiduity and strict adherence to the evidence of facts (as soon as he shall deem them sufficiently complete), will be a most important service rendered to practical navigation."

MATHEMATICAL EXERCISES.

1. What curve does the cross of St. Paul's Cathedral (lat. 51° N.) describe every twenty-four hours?

2. There are two stone pillars whose perpendicular heights are twenty and thirty feet, and the distance between them sixty. A ladder is to be placed at a certain point in the line of distance, of such a length that from thence it may just reach the top of both the pillars. Where is that point, and what is the length of the ladder?

3. The slant height of a wall is equal to twice its horizontal thickness; find its inclination when it will be just supported. (Proposed by Mr. Thomas Hogan.)

4. Find the centre of gravity of the three squares described on the three sides of a right-angled triangle.—(Also proposed by Mr. Hogan.)

Answers to be sent in to the Editor before the 1st of November, when the best of those then received will be selected and published.

a2 - b2

..

X

-

-bxdx

· (a2 — x2) †

dx

(a2 — x2)3.

a

+ æ.

a2

Note.

14

BRIGGS'S STEAM-ENGINE-HARDENING THIN STEEL PLATES.

Sir, I cannot allow the sneers of your correspondent, Mr. H. M. Briggs, (No. 310, p. 356,) to pass unnoticed; and let me tell him, that if his engine will not stand the test of that science which he seems so much to despise, he had better never bring it before the public. Has Mr. B. ever heard of Mr. Perkins? has he ever heard of the American Buchannan? and a host of other wonder-working engineers, who have shared the same fate? And if the intelligent and scientific Mr. Gillman was obliged to acknowledge that he had been deceived by his experiments and models, it will not be surprising (notwithstanding his present confidence in his discovery) if Mr. B. should hereafter occupy a page in the chapter of blunders, instead of a niche in the temple of fame. Is Mr. B. really aware of the amount of what he has promised to perform? If he is, I scarcely know what to think of him; if he is not, will take

the liberty of informing him. He has promised that, with the same expenditure of steam, he will perform eight times the labour, or, in other words, that he will overcome eight times the resistance. I am supported in the above assertion by Mr. Tredgold; see "Mechanics' Magazine," vol. iv. page 431. But perhaps Mr. B. has made some discovery analogous to that of Mr. Chapman's (page 74, vol. xi.) for "boiling cold water or other liquids," if so, there can be no question that a great saving will be the result of his discovery.

In reply to A Plain Mechanic," (No. 276,) I would observe, that if his steel plates are intended for saws, they must be heated in a furnace, taking care that the heat is not too high, for a high heat destroys the quality of the steel. When the plate has acquired the proper degree of heat, it must be taken out, and plunged edgeways into a composition of oil and tallow, to which some add a portion of pitch; the oil, however, forms the principal part. After being hardened, it must be taken and tempered over a charcoal fire to the proper degree of hardness, which varies for particular purposes. The plates must then be hammered

*

flat, and then ground. The hammering, however, destroys the spring required in tempering, but may be restored by holding it over a charcoal fire until it appears of a straw colour. It must be observed, however, that the above process is not the work of any single individual. The hardening is an art, the hammering is an art, and the grinding is an art; each of which requires some experience, which cannot be taught by any written directions. I remain, Sir,

Your very obedient servant,
A. MACKINNON.

Sheffield, August 3, 1829.

NEW METHOD OF OBTAINING THE DISTANCE BETWEEN THE SUN AND MOON, OR BETWEEN THE MOON AND A STAR, IN ORDER TO FIND THE LONGITUDE AT SEA.

Sir,-Having been engaged for a series of years in teaching nautical astronomy, and those sciences connected with it, and having had occasion to examine most of the authors who have more immediately devoted their attention to this useful art, I have found none who has farther illustrated this science than the late Dr. Mackay, author of an admirable Treatise on the Longitude: indeed, Robertson's Navigation, and Mackay's Longitude, are first-rate books on the subject. The great difficulty attending the nautical art is to determine the longitude at sea; and various methods have been employed for this purpose. It has

tion.

been discovered, however, that finding the true distance between the sun and moon, or between the moon and a star, is the best at sea that can be practised at present. From refraction and parallax, however, this great problem has been attended with considerable difficulty in its mode of calcula"The method of reducing the apparent to the true distance (says Mackay), or, in other words, that of clearing the apparent distance from the effects of refraction and parallax, being the most tedious part of the calculus for ascertaining the longitude, when the calculation is performed by the common spherical analogies, many

⚫ Page 149, 3d edition, London.

the same sovereign which we saw about three weeks since, in a shop in this town, with the appearance of having been dipped in quicksilver, being partly silvered over, which appearance was removed by the application of aquafortis, at our suggestion. We wish some of our philosophic readers would inform us if there is any mode of recovering the precious metal from the deteriora. tion occasioned by the contact with mercury.

.

INQUIRIES.

Sir, I will thank any of your correspondents for information on the following questions: Who was the inventor of chain rigging? Was ever a patent granted for it? (I have some reason to suppose there was about the year 1804.) In what name was it granted?-when ?-and for how long? Whether such rigging has been used in the Royal Navy, East India Company's service, or any other service ?, and to what extent ?

I am, Sir, yours, &c.
Huddersfield

Y.Y...

NOTICES TO CORRESPONDENTS.

The "Method of Extracting the Fifth Root," with which Mr. W. C. has favoured us, is, as he himself states, not to be "always found in books of arithmetic" but the reason of its being generally excluded from them is one which operates with equal force against its admission into the pages of the "Mechanics' Magazine"-it is of no practical use.

The New Methods of performing Practice by means of Reduction," &c. by the same correspondent, are all very well known. We beg,. however, he will accept our thanks for his good intentions.

Marima and Minima.-We hope Mr. Hall will agree with us that this subject is already in very competent hands, and had better be left there. Mr. H.'s paper appears to have been written before the appearance of that by G. S.

We have a letter from Mr. Foord, in which he "returns his grateful acknowledgments to O. C. F. and G.S. for their several remarks and criticisms on his method of lines for finding angles," but maintains that his errors were not so considerable as G. S. has represented, being only about seven degrees instead of thirty, &c. G. S. has himself frankly admitted this in our last Number. Besides, Mr. Foord need not be informed that a degree in land measuring is like an inch to a nose-a great deal.

We shall publish, in the course of a week or two, a communication from our esteemed correspondent P. M. W., which will be worth apples of gold to practical men. It is a table, on a single page, of natural sines, cosines, tangents, cotangents, secants, and cosecants, to every degree of the quadrant, with explanatory observations; by means of which civil and military engmeers, surveyors, architects, &c., may, without having recourse to logarithms, be enabled, by simple operations in decimal arithmetic, to solve all problems in trigonometry with the greatest accuracy. The celebrated Lalande is said to have been more proud of his portable logarithm tables, which sold for four francs, than of all besides that he ever published; but, justly prized as these have been, we hesitate not to affirm, that this little table of, P. M. W.'s, which will not cost the tenth of that sum, will be found of tenfold greater practical utility. Is "Mathesis" the same person of whoin the poet writes

Mad Mathesis alone was unconfin'd,

Too mad for mere material chains to bind?"His Theory of Nature" is left for him at our office.

The notice to "Watch Finishers" is an advertisement, but may have a place on the cover of the Monthly Part, on payment of the usual charge.

Mr. Taydhill's communication has been recovered, and shall have an early place.

Communications received from Mr. WoolgarMr. Saul-Mr. Baddeley-S. P. W.-O, C. F G.S.-Mr. Murdoch-Mr. Hopwood-Z.-J.O.B, -J. W.-Mr. Webb-T. G. S.--Hindostano-Mr. Taylor.

Published, for the Proprietor, by M. SALMON, at the Mechanics' Magazine" Office, No. 115, Fleet Street; where Communications for the Editor (post-paid) are requested to be ad- 1 dressed,

J. MOYES, Took's Court, Chancery Lane.