Imágenes de páginas
PDF
EPUB

We earnestly recommend our young engineers and mechanicians, to lay aside the alarm they generally express, when the study of the calculus is recommended, and to make an effort, if merely as an experiment, to read this work. We venture to predict, that if they do, they will feel that a film has fallen from their eyes, and that their right hand has increased in cunning. New and unexpected scenes of enterprise will open upon them, and an exquisite sensation of newly acquired power will irresistibly urge them to enter, and gather part of the immense harvest which yet awaits the sickle of the accomplished reaper.

There can be no doubt, that facts in the processes of art, and in the operations of nature, extremely simple in their appearance, but, perhaps, of immense importance, either for application or explanation, are daily passing unobserved, or if observed, soon forgotten and lost. The latter principally proceeds from the incapability of the observer to reason upon such phenomena, even when his natural sagacity teaches him to suspect, that they may be far more valuable than mere novelties. No class of men are likely to be so fortunate in this respect, and, if ignorant, to be so perplexed, as the rising engineers and mechanicians of the age. The powerful natural agents now under the control of man, and ministering in a thousand ways to his convenience and gratification, are daily presenting new data; from which, also, are daily proceeding new trains of reasoning and research, pointing towards results which, but a few years previous, even the human imagination had not dared to approach. Such results, however, demand the calculus for their easy and complete attainment.

To return to the work under consideration, we cannot completely discharge our duty, without stating our regret, that the author has omitted the answers to the exercises, and has placed the explanation of the signs used in the work, at the end of it, without any notice of them in the contents. The first, we are disposed to consider, as a material deficiency, and will be particularly felt to be so by the remote and solitary student. There may be some objection to placing an answer immediately after the proposition: the premature conception of it, so given, may injuriously influence the inquiry, and substitute for the mental exercise intended, another of a totally different character; but this will not apply, at least in the case of an honest inquirer, to placing it in an appendix. The answers are sure to be demanded even by the most able student, and a key will, therefore, be wished for, probably long before it can be obtained; and not then, probably, without additional cost. When it is published, we fear we must request of the learned Professor to elucidate his “illustration" at p. 18:- proceeding“ step by step :" there is nothing preceding this illustration that enables the learner to see that u=ays, and at the same time=2 x 109 x 2.

The book is very well printed, and the price not unreasonable ; but we wish, on account of a large class in whose hands we could desire to see it, that it had been possible to have published it at much less.

3

MISCELLANEOUS INTELLIGENCE.

Annual Depth of Rain in England. A VERY accurate observation has been regularly made for several years of the rain which has fallen at Kendal, in Westmoreland; and we are enabled by the kindness of Mr. Wakefield, a resident, to present a table of the quantity which has fallen in that neighbourhood during each month for the last seven years. The depth of last year it will be seen, amounted to 554 inches, which is very nearly the mean of the six years previous.

It would be interesting and useful to compare this return from a country of mountain and lake, and situated in the northern part of England, with others made as carefully, from districts of different surfaces and positions throughout the three kingdoms, and we shall be obliged by receiving such; and if accompanied by a description of the instrument, their position with regard to the ground, &c., and other details, they will be still more acceptable. ANNUAL MONTHLY DEPTHS OF RAIN WHICH FELL AT KENDAL DURING THE

LAST SEVEN YEARS.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small]

Aurora Borealis. The Aurora on the evening of November 18th, 1835, was witnessed with great brilliancy at Oxford. A low, broad, luminous arch stretched along the n.w. horizon at its centre, not rising to any great elevation : this remained quite stationary, but from it other bands or streams of light shot up. One observer saw a number of them together, which ascended to the zenith, and converged like the ribs of a dome. Others saw only a few, perpetually shifting, but of no great height; whilst one stretched upwards to the zenith, and beyond it, and was continually flickering and waving.

Curvilinear Direction of Winds. CAREFUL and continued observations, contained in the annual reports furnished by the several academies in the state of New York, to the Regents of the University, appear to demonstrate the fallacy of the notion commonly en Vol. I. F

1

tertained, that winds are generally rectilinear in their progress, and blow for the most part in right lines over extensive portions of the earth's surface; an error which appears to remain undisturbed in the minds of most meteorologists.

Temperature of Canton and Macao. Mr. MEYEN, for some time a resident at Canton and Macao, states, as the result of his own observations, and those of other residents during very considerable periods, that the mean temperature of Canton is 714. Fabr. and that of Macao 727° Fahr. It will facilitate accurate comparison to remark that the mean temperature of London, as stated by Professor Daniell, is 491° Fahr.

Filtration and Cooling of Light. M. Melloni, in examining the correctness of his opinion, that light and radiant heat were produced by different causes, and that there was therefore a possibility of separating them from each other when combined, has succeeded in accomplishing this remarkable experiment. By a process extremely simple, he separates light from radiant heat, whether proceeding from ordinary fires or from the sun. His mode is this :-The radiation from a luminous body is passed through a system of diaphanous bodies,—these absorb all the radiant heat, and extinguish but a very few of the luminous rays. The pure light emerging from such a system is found not to affect the most delicate thermoscope, even when concentrated by lenses to a brilliancy equal to that of solar light. The substances hitherto employed in this heat-absorbing system, are water, and a peculiar kind of green glass, coloured by oxide of copper. The cooled and filtered light, as it may be termed, is decidedly yellow, with a tint of bluish-green.

Periodic Appearance of Shooting Stars. M. Arago has recently given publicity to the notion that millions of groups of opaque bodies floating in space, may in their periodical revolution, annually cut the path of the Earth near that point of the Ecliptic where our planet may be found about the middle of November; and that on entering into our atmosphere, these bodies may inflame, and so become visible to us. He draws this conclusion from the reports of several observers of different nations, who have described appearances of this class of meteors which were remarkable for numbers and brilliancy; but more particularly for the circumstance, that though observed in different years, they all occurred on or about the 13th day of November.

Velocity, fc., of Currents in Rivers. M. de FONTAINE, an engineer long employed upon the Rhine, has published an elaborate work descriptive of his actual operations upon that river during twenty-one years. In it the author states the result of his numerous experiments, to determine the law of the variations in the velocity of the current of a river, which take place between the surface and the bottom. He finds the line of mean velocity always to be upon the surface when the bed of the river is clear, smooth, and continuous; and that it descends and approaches the bottom, in proportion as the bed is irregular, and as the number of obstructions lying upon it is increased. M. de F. has also ascertained, that a line, supposed to lie upon the surface of a river, at right angles to its shores, and free to move in a vertical plane only, varies very much in its form, though gene

rally supposed to be straight and horizontal, as A, B, in the annexed figure. This, M. de F. shows is never the case, except when the flow is uniform, and the height of the water is permanent; but that when the river is rising, this transverse line becomes more or less convex, as A, C, B; and, that on the contrary, it dips in the middle, and becomes concave, as A, D, B, when the river is falling.

[graphic]

M. de F. suggests, that the well-known differences of opinion which exist between professional men on this subject, may be principally owing to one or other of these particular cases only having been observed, and erroneously considered as a general law. The instrument used in these experiments on the velocities, was invented by M. Wattmann, an accurate account of which we should be happy to receive for the purpose of publication, and of comparison with one lately constructed in this country for the same object, and which will be described in our next number.

Variation of Temperature in Rocky Strata. Mr. W. HENWOOD conceives that he has satisfactorily ascertained that a difference of 20—3° Fahr. exists in the temperature of the schistose and granitic strata of Cornwall, when they are severally examined at the same depth. It is not stated to which the higher temperature belongs.

Reflected Heat measured. The fact that heat is reflected more or less abundantly in proportion to the nature and polish of the surface upon which it impinges, was confirmed by the researches of Rumford and Leslie; but these philosophers did not proceed to ascertain the proportion, in each particular case, of the incident, to the reflected, heat. It is easy to imagine a variety of cases in which, the property of the reflection of heat being known, and also that its quantity was variable, it would be desirable, and often exceedingly useful, to be able to ascertain the amount which could be obtained from any particular body and surface. M. Melloni has recently shown, that by means of an apparatus, designed by him, the problem can be solved with great accuracy. Another instance in which the genius of M. Melloni, aided by the exquisite delicacy and sensibility of his apparatus, has detected and exhibited properties and proportions of this invisible and universal agent, which appeared a short time ago to lie far beyond the utmost reach of the powers of man.

Flowering of a West India Plant in the Open Air. At a Meeting of the Ashmolean Society of Oxford, on the 6th of November last, Dr. Daubeny exhibited a specimen of the Bromelia pingiis, a native of the West Indies, which flowered last autumn in the open air in the garden of Mr. Shirley, of Eatington Park, near Shipston-upon-Stour. This plant has rarely blossomed in Europe even under glass, although a drawing of it in

F 2

[graphic][graphic]

இன்பார்ம் ties as h

மாலவன் வy alaliration

[ocr errors]
« AnteriorContinuar »