« PreviousContinue »
ocean may be considered as nearly independent of the tides of other waters. The central area of each ocean is occupied by a lunar wave, which oscillates, keeping time with the moon's returns, and having its motion kept up by the moon's attraction acting at each return. From the skirts of this oscillating central area, tides are carried on all sides by free waves, the velocity of which depends upon the depth and local circumstances of the sea; and thus the litoral tides may travel in any direction, while the oceanic tides near the centre of the oscillating area may be small or may vanish altogether.
This theory was confirmed by a reference to tide observations on the eastern and western sides of the Pacific, and by mathematical calculations tending to show that such a motion is mechanically possible. It was remarked that single observations can be of small use in deciding upon such a theory; and that it can be judged of only when we have observations numerous enough to enable us to draw the systems of cotidal lines which belong to the shores of the Pacific. With this view it is very desirable to obtain numerous and connected observations of the tides on the eastern shores of Australia, the Indian Archipelago, the Philippine Isles, the Loo Choo Isles, and Japan.
This theory to a certain extent coincides with the views respecting the tides published by Capt. Fitz Roy in his appendix to the voyages of the Adventure and Beagle.
L. & E. Philos. Mag.
The Bude Light.
From the minutes of an examination of Goldworthy Gurney, and Dr. Faraday, before a committee of Parliament, on the Bude light which has been adopted as the mode of illumination in the House of Commons, it appears that this light is called the Bude light in reference to the residence of the former gentleman in Cornwall, where the experiments were made. His name was associated with the same light which we published an account of in 1823, and this was called the Bude light at the Trinity House by way of distinction.
The light is produced by throwing a stream of oxygen gas into the flame of a lamp, shaped like a small Argand. The interior of every flame being hollow, the vapour of the oil and the carburetted hydrogen is constantly liable to escape unburnt. The oxygen strikes the vacant carbon and vapour of oil as it is distilled, and produces an intense light.
Dr. Faraday testified that Gurney's lamp burns with remarkable steadiness for eight hours together, not requiring so much attention as an ordinary Argand lamp for the same time. There is no fear of danger from explosion, and the light can be managed by any person of common dexterity. The bur ners in the Bude light are rather more than a quarter of an inch in diameter and sixty burners consume about three pints of oil per hour. The lamps are so arranged that they can be raised and lowered to the amount of several feet, and the oxygen being brought to the light in small flexible tubes, the light may be moved about at the time it is burning.
Taking the price of manganese at 8 to 9 £ per ton, and estimating the usual wear and tear of apparatus and expense of fuel and attendance, the oxygen costs about 2d a cubic foot. There is an inexhaustible supply of manganese in Devonshire and Cornwall.
The lamp burned by Dr. Faraday gave a light of 20 Argands of inch
in diameter, and in twelve hours burnt six and four-tenths pints of oil, and used sixty-four cubic feet of oxygen. This he considers as the best proportion, though there is such power over the lamp that it can be increased to almost any intensity.
Abstracted from a statement of the examination in the Nautical Magazine for November, 1839.
Progress of Civil Engineering.
New Overshot Water Wheel.
The great overshot wheel, erected by the Kilgetty Colliery Company, at Merrixton, near King's Moor, Pembrokeshire, was set to work on Saturday the 7th ult., in the presence of a large assembly of the ladies and gentlemen in the neighbourhood. This wheel, we believe, is the most powerful in the principality, being of 75 horse power; the diameter is forty-feet, and it is seven feet wide on the breast, and the buckets hold water more than one-third of the circumference. It is fixed in a manner that is quite novel in this country, the wheel being so closely shut in by finely-executed masonry, that the escape of water, without going to the buckets, is impossible. It works by eccentrics, giving a horizontal motion to the cranks, being the first application of this mechanical arrrangement to such a purpose. It is adapted to work two pumps, giving twelve strokes a minute to each pump. The water is diverted from the stream about two miles from the wheel, and it is brought to it across the valley by an aqueduct, extending 300 feet in length, and from thirty to forty feet high. The wheel will supersede the use of steam power in the colliery, and it is contrived that, in time of drought, the water to be raised by the wheel will assist to drive it. The whole arrangements of the wheel are new applications of mechanism, and great improvements on plans hitherto in use. Considerable attention has been given to these works by parties who are not interested in them; and in the immediate neighbourhood, where so much enterprise at the present moment is in active operation in mineral undertakings, they well deserve the attention of all parties engaged in such enterprises. The works are close to the new road leading to Hobbs' Point, and may be conveniently inspected by parties travelling that way. The wheel and machinery were designed and executed by Mr. Thomas Dyson, of Downham, in Norfolk, where the wheel was made, and he has personally superintended the execution of the whole work. Although the wheel was made in order to drain the mine by pumps, it is understood the parties have since been advised to try instead the patent hydraulic belt, and intend to adopt it. A model was exhibited, and excited much surprise at its simplicity and its effective power to raise water on a small scale.
Lond. Mech, Mag.
Statistics of the Iron Trade. By HYDE CLARKE, Esq., C. E.
In 1826 this country was visited by a French statistician, M. de Villeghem, for the purpose of investigating the state of the iron manufacture, and he has given an estimate of the number of furnaces in that year, which seems generally accurate. The following is a table of the progress of each district, as far as it can be made out from the several authorities, although they are mixed up very confusedly. The returns of 1802, 1820, and 1827,
are from the Parliamentary returns; 1826, from the French estimate, and 1839 from the one given in the previous article.
400,000 305† 284 690,000 417 1,512,000 The following is M. Virlet's estimate of the amount of iron annually produced in Europe in 1835, with an annexed column of corrections to the present time:
England produces about one-half the whole quantity, France about a fifth, Russia, Sweden, Austria, and Prussia, each about a twentieth. The total produce must be about three million tons.
Total in blast. † 280 in blast, produce 728,000 tons.
The following, illustrative of the importance of the English iron trade, is a comparison of some of the European, English, and French iron districts. It may be premised, by the bye, that South Wales alone produces about as much as all France put together, and Staffordshire, Scotland, and Shropshire, each surpasses any other European country:
In concluding this subject it may be noted, that, for the service of the South Wales district alone, 300 miles of railway are constructed.
Difference of Longitude between Greenwich and New York.
I have the satisfaction to inform you of a second instance of the successful transport of chronometers from London to New York, for the purpose of determining the longitude of these two cities. The first, as you will remember, took place in the months of July and August last. The result then obtained was compared with that given by M. Daussy, a distinguished French hydrographer, in the Connaissance du Tems. The difference of these results was 2.63 sec. This was satisfactory under the circumstances of a first attempt, made in the first trip across the Atlantic of the British Queen; still I felt the difference to be too great to be permitted to remain without an attempt to diminish it, or to ascertain which of the two was nearer the truth. On the very next voyage, therefore, of the same vessel, and under the same friendly auspices of Captain Roberts, and my friends in the United States, I sent a second set of four chronometers from London to New York. Their rates, &c., were ascertained precisely as those of the first set, and the whole experiment conducted in the same manner. This voyage of the British Queen was made, out and home, in the last and present months. The result, I have the pleasure to announce, is this time, almost exactly the same as that of M. Daussy's; so near, indeed, that I feel it to be a duty, and one of the most pleasing nature, to express thus publicly my great admiration of the accuracy of his statement:
The difference of the two observations does not therefore amount to half a second! For all the purposes of practical navigation it may be regarded as nothing.
This very minute variation in the estimates of the astronomical distance
of two meridians so widely separated as those of London and New York, will be very gratifying to every lover of practical science both in France and England, the more so, when it is considered that these estimates were made independently of each other, "by different observers, in different years, and in vessels propelled by different agents." Perhaps it ought not to be omitted, that in both the English experiments the instruments were sent out unattended by any savant, and brought home their own report.
During the first voyage there had been observed in all the chronometers, a difference between the mean travelling rate and the mean stationary rate, which had the remarkable character of being always on the same side, viz., the losing rates were always increased, and the gaining rates always diminished. The same curious fact again occurred in the second voyage. From this circumstance the longitude of New York was given by each chronometer scarcely enough to the westward in the outer-bound voyages, and rather too much so in the homeward ones.
The great rapidity and accuracy with which this important branch of nautical inquiry may be pursued over the whole surface of the globe, as the agency of steam shall be extended, is now, I think, demonstrated. The instances under consideration show that observations may be made connecting very distant countries, and their several results compared in a few weeks -a circumstance of great consequence-for with the diminution of duration in a voyage, proceeds, in a higher degree, the diminution of all the chances and causes of error in chronometrical experiments at sea. Within the space of ninety-nine days, we have seen the British Queen carry chronometers four times across the Atlantic, and give ample time during each other of her visits to New York for the necessary observations of rates, &c.
All objections founded on the idea that the motion of a steam-vessel would affect injuriously the more delicate movement of the chronometer, and taint the results, must now fall to the ground. In the two voyages out and home of the British Queen, no derangement occurred, and the determination of the longitude of the far-distant ports she sailed between, is, probably, settled for ever, within the fraction of a second of the truth.
Instrument for Ascertaining the Temperature of Water at Great Depths.
In the extract which we published (p. 188) from Dr. Paterson's account of experiments on the temperature of Artesian Wells, an instrument is referred to as used by him in the course of his inquiry. At the request of several correspondents we take a further extract from the Doctor's interesting paper in the Edinburgh New Philosophical Journal, describing this in
"That objections might not be brought against this species of information, we used an instrument which has been long known for ascertaining the temperature of water at great depths. It consists of a glass-tube with brass ends which screw on; in each of these ends there is placed a valve, and both of the valves open upwards. It contains a thermometer, and is surrounded with a non-conductor; a string being attached to it, it is lowered down into the bored well. The water rushing up the bore, together with the instrument descending against it, causes both valves of the instrument to open, by which a free communication through the instrument by the valves is kept up, until it reaches the bottom of the perforation. The instrument is to be