ePub 版

theory was ingenious and worthy of attention. It would be curious to see what relation to phy sical forces the orbitual and diurnal rotations may have.

The principal point submitted to the section was the subject of winds, and their relation to the barometer. There appear to be two kinds, -winds of translation and of oscillation. The trades, monsoons, &c., are examples of the former; the latter are winds of local origin, prevalence of rains, &c. It is desirable to make out the law of these movements, and to this end the reduction of the observations is to be continued by Mr. Birt. Already there are marked manifestations of Brussels being a nodal point, and hence hopes of success.

Since the last meeting of the British Association, the committee have obtained and published, in the 11th and 12th numbers of Taylor's Scientific Memoirs, translations of the four following works: Gauss's Dioptric Researches; Dr. Lamont's Account of the Observatory and Instruments at Munich; Gauss's Magnetic Observations at Göttingen; and Lamont's Magnetic Observations (three years) at Munich. No portion of the grant placed at the disposal of the committee has been expended; and this is to be attributed, if we rightly interpret and apply what fell from Sir W. Hamilton, to the acquirements and industry possessed and devoted to the advancement of science by the accomplished lady of the gallant colonel.

to the surface of the glass. Although the result is exactly the same as Fresnel predicted, the laws of total reflection have never before been ́ explained. The explanation, moreover, applies to doubly-refracting crystals, or to the refraction of a crystal in a fluid of a higher refractive power. The laws are extremely beautiful, and completely connect Fresnel's laws of double refraction with the laws of insensible refraction and total reflection.

Dr. Peacocke (chairman pro tem.) proposed the thanks of the section to Prof. M'Cullagh for this exposition of his important researches. He designated the realizing Fresnel's anticipation as the greatest march ever made in physical optics.

The labors of the committee are proceeding. German works which may influence their decision have been ordered. The final report may be expected to be ready for the meeting next year.

The observations conducted by Prof. Lloyd in the magnetic observatory of the University of Dublin extended over a period of four years and a half. The elements observed were, 1, magnetic declination; 2, magnetic inclination; 3, horizontal component; 4, vertical component of the total force. They were not, however, all accurately observed from the first in 1828. There had been a difficulty in obtaining the third element, which difficulty, however, he had overcome. The results of observation were given in Total reflection is a problem in physical optics a diagram, showing the diurnal changes of dewhich has long excited curiosity, and baffled re-clination and inclination for the summer months, search. Newton's explanation of it affords no account of the phenomena in cases of polarized light. He considered, however, total reflection to be an insurmountable proof against the undulatory theory of light; and this opinion, very generally adopted, retarded the progress of this science for a century. Poisson was the first to see the mode of solution, by imagining the motion in one direction of two fluids superposed, the one of greater density than the other: the motion would not pass into the rarer medium, and hence the common method of expression was not available, the expression being by sines and cosines multiplied by exponential functions. Fresnel, however, made the greatest advance; he formed certain formulas and expressions, reduced from values verified by experiment, for refracted light. But of refractions beyond the surface he could form no conception; he labored for six years, but he had not the dynamical equations for the motion of light in transparent media. Prof. M'Cullagh found them by conjecture in 1835. He only has recently applied them, and has been able to assign not merely the laws of insensible refraction, but also to explain the nature of total reflection, and to prove each by mutual confirmation. He described the laws of insensible refraction, dependent on the motion of the molecules in rarer medium, being elliptic, not rectilinear, the elliptic vibrations increasing in magnitude as they recede from the glass. In one case only will the vibrations be right lines, and that is when light is polarized vertically. When polarized in the plane of incidence, the vibrations are ellipses, the minor axes being parallel and the major perpendicular

for the winter months, and for the whole year. First element; the change of declination is extremely small during the late hours of night and those of early morning-it decreases to 7 A. M. and then rapidly increases, motion westerly, to maximum at 1 P. M.; the succeeding maximum is at 10 P. M. In summer the evening maximum disappears, in winter the reverse takes place; also for the morning maximum, which is well marked in the summer months. The maximum easterly movement is 7 A. M., minimum 1 P. M. It does not reach a maximum in the afternoon, it increases to midnight but slowly, and then faster to morning maximum, and afterwards decreases rapidly. The daily range is greatest in August, being then 13'7; least in January, 7-2. The mean daily range for Dublin is 9-3 minutes. One remarkable fact, however, is, that the period of the minimum at past 1 P. M. is nearly constant during the year. Second element: magnetic inclination has two maxima and minima during the day-a minimum at 3 A. M., maximum 5 A. M.; principal minimum past 10 A. M., principal maximum 6 P. M. In the summer months the morning fluctuation is obliterated. In the winter months the double maxima and minima appear, and also a third maximum, the evening maximum breaking into two. The daily range is greatest in July, 0·0045; least in January, 0.0008; mean, 0·0024. Third element, obtained by balance-magnetometer and by induction, whence are deduced the changes of total intensity and inclination: inclination greatest past 10 A. M., minimum between 5 and 6 P. M., extending in winter to 2', and in summer to double that amount. It corresponds nearly in

The author then mentioned the theory of M. Fizeau, which theory has been followed by some others, who attribute the formation of these images to an organic film of a volatile nature, which he supposes diffuses itself over the surfaces of all bodies. It was contended, that if the impressions were thus formed, they would exist only on the surface of the plates, whereas it had been found that a molecular change was produced to some considerable depth in the plate, that many surfaces might be removed, and still the image rendered apparent. Several experiments were instituted, in which copper plates carefully polished with polishing stones and water, and then boiled, and so dried that any or

period with the intensity, the curves being similar, but inverted. There appears to be a daily change in the total intensity decreasing to 9 A. M., increasing with double maxima and minima in the afternoon; and so remarkable as to lead to the belief that these phenomena depend on the sun. But on farther experiments and comparisons, Prof. Lloyd was led to conjecture that there were other causes than the direct action of the sun, acting indirectly. The change of total force appears to observe law, but it is extremely small in comparison with the changes of declination and inclination. The observations to determine the annual or secular change are not yet numerous enough; but he hoped to complete them before the next meeting of the Asso-ganic matter must have been removed. On these, ciation.

Col. Sabine spoke to the great interest attaching to these observations, and to the prodigious labor given to them in Norway. The observations have been taken there every ten minutes, day and night, and the results are in course of reduction.

Dr. Scoresby communicated the results of his experiments on the circumstances which affect the energy of artificial magnets, their mutual relation, influences, and anomalies. He spoke also of the value of large magnets for locomotion, and of their being so much more useful to this end than electro-magnets. He has constructed a magnet that will support a ton weight.

After mentioning the views entertained by Möser and Draper, and remarking on the very unscientific nomenclature of the latter, the author proceeded to show that the hypothesis of latent light radiating in darkness, was quite uncalled for and unnecessary in explaining these very remarkable phenomena. That the effect is due in some way to the calorific element, the author thinks he has proved by the following experiments. A condensed prismatic spectrum was kept fixed by a good heliastat upon one spot on a plate of copper for three hours. The plate was then submitted to the action of mercurial vapor. The space covered by the visible chromatic spectrum was untouched by the vapor, which had deposited in a thin film over the other parts of the plate; but over the space occupied by the extra-spectral red ray the deposit of va por was much greater than on any other part, forming a well-defined white space. The experiment was varied by allowing a very condensed prismatic spectrum to traverse slowly over a copper plate for two hours. It was found, on exposing the plate to the vapor of mercury, that the space covered by the luminous spectrum was, as before, left free of vapor; but a well-defined line marked the path of the extra-spectral red ray. An arrangement was made by which, by means of colored media, the calorific, luminous, and chemical rays were isolated with tolerable purity. Under each of these, a copper plate, having a design in paper on its surface, was placed, and left exposed to the light of the sun for an hour. On removing the plates in the dark, and exposing them to the vapor of mercury, there was no impression found upon either plate, except the one under the influence of the red rays. This experiment was many times repeated, the results being in each case the same.

medals and coins, all of them carefully washed in boiling water, were placed, and allowed to remain for different periods. While, at the same time, plates and medals, which by rubbing with the hand had been covered with these supposed films, were placed alongside of them. All were examined in the same way, and the effects were nearly the same upon the boiled plates as upon the others. We select two of these experiments in illustration. On a copper plate, which had been kept for some time in boiling water, bronze and silver medals prepared in the same way were placed, the whole being at the temperature of 61.5 Fahr. The temperature was elevated by the spirit-lamp to 89°, and the whole left in contact until the thermometer fell to 62°. Breathing on the plate gave a defined outline of the space occupied by the silver medal, the vapor being deposited on the space covered by the rim. But the vapor of mercury attacked the plate generally, leaving the space corresponding with the rim quite free of vapor. Of the bronze medal there was no impression. It has been repeatedly observed, that when two medals, having in relation to heat different conducting powers, are placed on the same plate, that one interferes with the impressions which the other would have made if placed by itself. piece of plate-glass, washed with boiling-water and caustic potash, with a bronze medal, a sil ver one, a sovereign, and a shilling, placed on its surface, was placed under the receiver of an air-pump, and a good exhaustion kept up for 18 hours; a very distinct image of each of these coins and medals was seen when the plate was vaporized. Thus it appears to be proved that the action is quite independent of any organic film or deposit of dust, which has also been brought forward in explanation of these magical phenomena.

On a

The next paper in the list was No. 8. This supplementary report, the principal points of which only were submitted to the section, presents the results of experiments in a more complete shape than those which Mr. Scott Russell had formerly laid before the Association; the essential difference in the characteristics of the different classes of waves having been ascertained. In water there are four distinct classes of waves; of these the fourth is the common sound-wave, introduced merely to give completeness to the system. The third class had not previously been examined to any considerable extent, if at all. The following is the


classification of the whole:-1st class are called Mr. Hunt, after describing the process introwaves of translation; 2d, oscillatory waves; 3d, duced by Mr. Pontor, by which negative photocapillary waves; 4th, sound-wave in water. graphs were produced on paper by the use of Of these the first is always solitary, the second the bichromate of potash, and the improvements and third always in groups; the first class has introduced by M. E. Becquerel, with a view to two varieties, positive and negative; the second the production of positive pictures, but which has also two, stationary and progressive. There process was tedious and very uncertain,-gave are no varieties in the third and fourth. Be- an account of his new process, the chromatype, sides these species there are the following sub-and exhibited very interesting specimens of picvarieties, the free and the forced wave, in each tures produced by it. The process, which is class. Such is the natural history or classifica-exceedingly simple, is as follows:-paper is tion of waves. Their principal characteristics washed over with a solution of the sulphate of noticed were-velocity, motion of particles, re- copper, dried, and then washed with a solution flection, and diffusion. 1. The velocity. The of the bichromate of potash. When dry these velocity of the first class is represented by papers are fit for use, and will keep for any ✔g(hk), where h is the height of the wave, length of time unimpaired, if preserved in the and k is the depth of the channel. The velocity considerably varied, by which the shades of The strength of the solutions may be of the second is 3.57 x ✓ length of wave; the colour of the finished picture are pleasingly velocity of the third is 8.5 inches per second; changed. This paper is not recommended for the fourth is the well-known velocity of sound, 13.437. 2. The different kinds of motion of use in the camera obscura, but for all other purposes it is exceedingly useful. An engraving, the particles of water. In the first they un-botanical specimens, or the like, being laid on dergo a permanent and final displacement; the paper in a proper manner, it is exposed to the second an oscillatory or continued series of the sun's rays for a period varying, with the intemporary displacement; the third is the same. In the first the horizontal displacement is equal tensity of the light, from five to fifteen minutes. A very faint picture results from this exposure. at all depths; in the second it diminishes ac-It is then washed over with a tolerably strong cording to the depth; in the third it does not solution of the nitrate of silver, which brings out extend to a sensible depth below the surface of a very intense orange-colored image, the lights the water. In the first class the path of trans- and shades being correct as in nature. The only mission of all the particles is a semi-ellipse; fixing required is simple washing in pure water, in the second the displacement is a simple spi- and drying. If one of these chromatype pictures ral; in the third it is so minute as not to be as-is placed in a very weak solution of common certained. 3. Phenomena of diffusion and re-salt, it rapidly fades out, and the paper is reflection. The second and third classes are duced to its original whiteness. The picture, reflected according to the usual law. The first however, is not obliterated; if the paper is held does not appear to suffer complete reflection; but at considerable angles with the surface a curi- in the sunshine for few minutes, the images gradually come out, and the picture is restored; ous phenomenon is presented. If the angle which but instead of being of an orange color, it is now the ridge of the wave makes with the surface of the water be less than 30°, total reflection a fine lilac. This variety requires no fixing. takes place; from 30° to 60° it decreases, and ceases altogether from 60° to 90°; then, instead of being reflected, the wave advances forward, increasing in magnitude, until in a short time the whole wave is converted into another parallel to the surface. This phenomenon of nonreflection is peculiar to the wave of the first order. There is another curious phenomenon in waves of the first order; they are not diffused in circles round the point of generation, as in the common wave when a stone is thrown into the water; but from a given point there is always a direction in which the motion is most rapid; thus the path approaches an ellipse. The magnitude at different angles from the direction of greatest velocity has been ascertained: at 30° from the axis the intensity has diminished to a half, and at 45° to one-third of the greatest; thus the degradation follows a certain law. We cannot generate a wave of the first order except it be confined in a narrow channel. A stone dropped in the water will generate a wave of the second order, spreading equally in every direction. Capillary waves are in all cases confined to the surface of the liquid.

Chemistry and Mineralogy.-R. Hunt on chromatype, a new photographic process; and on the influence of light on the growth of plants.

Mr. Hunt's second communication was simply a statement of the results he had obtained since the report which was made by him and published in the last volume of the Transactions of the Association. Most of the results were in confirmation of those already arrived at; and all went to prove the injurious effects of the luminous and calorific rays upon the young plant, and the energetic and healthful action of the chemical rays. The author had, however, discovered that the continued action of those chemical rays in a pure state, exerting a most powerful stimulating influence upon the plants, occasioned the production of an extraordinary amount of leaves, and these of a fine dark color; but that the energies of the plant being thus exhausted, it could not be brought to flower, and speedily decayed. This influence of the chemical rays on the vegetable world was similar to that exerted by pure oxygen gas upon animals. The author also noticed a remarkable property which he had observed in the luminous rays, namely, that under their influence agarics grew very rapidly, but not at all under the agencies of the other rays; which fact appears to correspond with the experience of gardeners, who attribute great power to the moon's rays in producing this variety of plants.

The last paper was read by Prof. Kane. Prof.

As closely bearing upon this subject, we may add here Mr. Hunt's paper read in Sect. B. on Saturday.

Draper's theory is, that the decomposition of] carbonic acid by the leaves of plants is effected by the luminous rays of the spectrum, and not by the chemical rays. For the purpose of prov- The object of Mr. Hunt's communication was ing that, he took a series of tubes, half an inch to show the high probability that the rays which in diameter and six inches in length, and ar- emanate from the sun are constantly acting upranged so that the colored spaces of the spec- on all bodies, and that but for our ignorance of trum fell on them. In those tubes water, im- methods by which the impressions can be pregnated with carbonic acid, and containing a brought out, we should be enabled to use any few green leaves, was placed. He supposed body as a photographic material. In addition that if the decomposition were due to radiant to those combinations which were well known to heat, the tube occupying the red space, or even possess photographic properties, the author callthe one in the extra spectral space at that end, ed attention to the wonderful additions made to would, at the close of the experiment, contain the list by Sir J. Herschel, who had shown that most gas; if to the chemical rays, in the violet, the salts of iron and of mercury were very rapidindigo, or blue; but if to the luminous rays, the ly changed by light; and nearly all kinds of gas should make its appearance in the yellow, vegetable juices were changed by its influence. with some in the green, and some in the orange. The author was now enabled to add the results The result proved his anticipations. In the tube of numerous experiments, all of which went to in the red space a minute bubble was sometimes prove the decomposing power of the solar rays. found, but sometimes none at all; in the orange În addition to the salts of silver ordinarily used, a considerable quantity; in the yellow a very it had been found that more than twenty combilarge amount comparatively; in the green a nations with organic acids gave very beautiful much smaller quantity; while in the blue, the results; and that the cyanate, and arseinate, and indigo, the violet, and extra spectral space on sulphuret of silver, previously considered as inthat side, not a single bubble was observed. He sensible, were really acted upon with great rastated that he decomposed the alkaline bicar-pidity. Combinations of gold with cyanogen, bonate by leaves in the sunshine-the effect not and benzoine, and many other bodies, proved being limited to the removal and decomposition the readiness of this metal to change in the of the second atom of the acid, but passing on to sun's rays. The salts of platinum were also the first-the neutral carbonate of soda itself de-found to be rapidly affected; and some pleasing composing, and yielding oxygen gas. He also photographs on papers prepared with combinamentioned an important improvement on the tions of platina were shown. Mr. Hunt had also tithonotype, and a new process of multiplying been successful in proving this change to take daguerreotypes. For the latter, his old plan place under the same influence on nearly all the was to evaporate to dryness on their surface, af- salts of copper-many of which changed rapidter being fixed by a film of gold, a solution of ly, and produced very pleasing pictures—and, as gelatine; but his new is to precipitate copper by far as they had been yet examined, on the salts the electrotype on the surface of the daguerreo- of manganese, of antimony, of tin, of lead, of cotype, after it has been fixed by gold. The cop- balt, and of arsenic. In addition to these, many per being much more tough than the gelatine, of the cyanates, the ferrocyanates, and the separates readily from the silver, and, when the iodides, with alkaline bases, were found to change operation is successful, bears a perfect represen- with considerable rapidity. Many of these pretation of the beauty and perfection of the origin-parations which had received photographic imal picture. Prof. Draper considers this method totally different from the attempt which many persons made to copy the daguerreotype by voltaic electricity, and that, in consequence of the ease with which they are made, the problem of multiplying the daguerreotype may be regarded as solved.

ages were shown to the section; and the author expressed his regret that, from the fleeting character of some of the most interesting of these results, he was unable to do more than describe the effects.

The author then detailed many very remarkable phenomena which were presented by reProfessor Apjohn questioned the results an-ceiving the impressions of the prismatic specnounced by Prof. Draper, and called on Mr. Hunt, who had experimented so much on the subject; who confirmed his opinion that the chemical and not the luminous rays were the most efficient in producing the decomposition of the carbonic acid absorbed by the plant. Mr. Hunt described his experiments on plants with colored glasses and with glass vessels filled with colored media; and, from every result he had observed, differed entirely from Prof. Draper. He would resume his study with the rays of the prism;* and, in conclusion, he mentioned certain peculiarities in the vegetation of South America, which seemed to lead to the conclusion, that there existed a difference between the effects of light in southern and northern climes.

Assuredly the best method, and freest from suspicion of chemical interference.-Ed. L. G.

trum upon different sensitive materials; all of which went to show the necessity of separating from light and also from heat that agent which was active in producing these changes which have been described. This element had its origin in the sun, and always accompanied the rays of light and heat; but its functions were different from either; and it appeared that we were on the verge of discovering an important power, which was ever active in maintaining that system of change which appeared to be constantly going on throughout the works of creation.

Geology and Physical Geography.-The next paper read was by Messrs. Rogers, on the phenomena and theory of earthquakes, and connected with the same mountain range. The

marine valleys, but by the up-heaving of the
earth from some internal convulsion the present
position was acquired.

Mr. Lyell held that floating ice was capable
of carrying larger blocks than any found here.
When melted it might deposit these blocks in
any place. This process was going on every
day in large parts of Europe. The shells in
Ireland and Scotland are found 700 feet high.
Mr. Murchison agreed with Mr. Lyell as to the
floating powers of ice. The great northern
plains of Europe offered strong proofs of this.
In Germany he had found large blocks on slight
acclivities, bedded in earth.

anticlinal flexures already alluded to were
ascribed to a billowy movement of the earth's
surface, like the phenomena attending an earth-
quake; and the two remarkable earthquakes
which had occurred within the year were refer-
red to as furnishing laws which confirmed in a
striking manner the supposed origin of the
Apallachian chain. All earthquakes consist of
a remarkable motion, which is not simultaneous
but progressive, and which moves parallel to it-
self from the source of disturbance. The author
referred to the observations of Capt. Fitzroy and
Prof. Mitchel in confirmation of his views, and
dwelt on the phenomena attending the earth-
quake at Guadaloupe and Antigua, and also the
earthquake at Lisbon. The zone of undulation
extended in all directions, and at sea the sym-
pathy seemed to be indicated by huge waves
remarkably isochronous, propagated at the rate
of five minutes after each other. Upon this hy-
pothesis the American writers relied for the ex-
planation of boulder stones, without resorting to
the glacier theory. Mr. Hopkins questioned the
law laid down for the organization of the Apal-
lachian chain by Messrs. Rogers. A fluid mass
beneath the earth might expand the outer crust,
but would a horizontal force produce such pow-made, the inclinations of the beds of glaciers
er? A horizontal crust, with a reservoir of lava
beneath, as in Vesuvius or Etna, might cause
a rising of the crust, assuming a curved form, but
the elevation would produce fissuring, and it
would be impossible to put it into the same form
as before. The fluid matter would be forced into
the fissures. Thus two causes would operate,
lengthening by tension and injection. Besides,
a wave was movable, and could not act in the
way laid down, nor could the elevations corre-
spond with successive waves.

Mr. Phillips, Mr. Murchison, and Major Clerke, also spoke on the subject, and doubted the accuracy of the theory.

Mr. Hopkins gave an exposition of his views respecting the cause of the motion of glaciers. De Saussure had adopted and expounded the theory which attributes this motion to the resolved part of gravity acting along the inclined surfaces on which all glaciers in motion repose; and he explained also how the motion would be facilitated by the effects of the internal heat of the earth, and of subglacial currents. When the attention of philosophers, however, was recalled a few years ago to this subject, and more accurate observations and admeasurements were

were found, in many cases, to be so small (in the glacier of the Alesch, for example, not exceeding three deg.) that it appeared extremely difficult to conceive how the force of gravity alone could be adequate to overcome the friction on the bottom and sides of the glacier, and the numerous local obstacles to its movement. Numerous experiments on the descent of bodies along inclined planes had shown, that, when the surfaces of the bodies and planes were perfectly hard and polished, no motion would ensue without an inclination considerably greater than that of many glaciers; and, moreover, that the inclination required to produce motion was independent of the Mr. Griffiths, on the great drift in Mayo and weight of the sliding body. These consideraSligo, noticed the position of the erratic blocks tions led to the very general rejection of De or boulders which occurred in these counties, as Saussure's theory, and to the adoption by many well as in other parts of Ireland. In the north persons of the dilatation-theory, of which M. part of the counties of Mayo and Sligo the cur- Agassiz had been the principal advocate. Acrent was from south to north, as was indicated cording to this theory, a part of the water proby boulders of red sandstone from the Corlew duced by the dissolution of the superficial portion mountains having been transported to the north- of the glacier during summer passed by infiltraward across the limestone valley of Ballymote tion into the minute pores and crevices of the to the base of the Ox mountains; and also, by glacier, when it was again converted into ice; large boulders of granite from the Ox moun- and, by its expansion in the process of freezing, tains, some of them weighing upwards of 100 produced a dilatation and consequent motion of tons, being now found in great numbers on the the glacier. It was manifest, however, that the surface of the limestone country to the north as frequent alternations of freezing and thawing far as the sea coast at Easky. Blocks of such within the glacier, which this theory assumed, large size were probably transported on ice, could not possibly take place at depths beneath though it was remarkable that in this case, their its surface exceeding a very few feet, and theredirection was from south to north. They were fore could not produce any sensible effect on the so numerous, that when he first came to Ireland, motion of the whole mass. If the effect were rehe thought it was a granite, not a limestone ferred to the freezing of water at greater depths, country. It was well known that the removal it could only be attributed at most to annual of these blocks was accounted for in different variations of temperature, and the consequent ways-by currents-floats or drifts of ice-and motion would take place during the colder seaglaciers. Limestone blocks might be transport- son, or at its commencement, and not during the ed by currents, but it was not so easy to account summer, when, as appeared by observation, the for the removal of the masses of granite. Some-glaciers moved most rapidly. If, again, the times shells were found on the tops of mountains, which could only be accounted for in this way, that these mountains had been once sub

dilatation were attributed to the freezing of the
infiltrated water at still greater depths, where
the temperature of the ice was unaffected even

[ocr errors][ocr errors]
« 上一頁繼續 »