troscope was so well known at the time of Teniers as to be included in the inventory of apparatus of a chemist's laboratory.

Is not the evidence that the theory of binocular vision and of the stereoscope were known at the time of Chimenti, quite as weak as would be afforded by Teniers' pictures, to disprove the modern invention and use of the spectroscope?

The Chimenti pictures must therefore be ruled out of court and judgment entered for Mr. Wheatstone, unless new evidence can be found worthy of the consideration of scientific men.

New York, June 1, 1864.

ART. XXI.-Results of some recent Observations of the Solar Surface, with Remarks; by the Rev. W. R. DAWES.'

DURING nearly the whole of last year and the first three months of this, the state of the air was rarely sufficiently good to permit a successful scrutiny of the solar surface with high powers on a large telescopic aperture;-on such occasions, at least, as I was able to make much use of. But on three or four days in April I found that vision was remarkably steady and distinct, and I improved the opportunities to the utmost.

As it was of considerabie importance that the same minute portions of the surface should be examined and compared together under various magnifying powers, and with different shades of dark glass, I preferred, after a careful comparison with the ordinary eye-pieces and an excellent transparent diagonal, to employ a solar eye-piece of my own construction, And I would take this opportunity of correcting an idea which has been advanced, that the diffraction of the rays at the edge of a small aperture in that eye-piece interferes with the distinctness of the object viewed. Close to the edge of the field there is, of course, as Mr. Huggins well expressed it at the last meeting of the Society, a narrow ring of diffracted light; but the breadth of this ring does not, I think, exceed 2" on my telescope; and the smallest aperture in the diaphragm-plate has a diameter of 15". Consequently, there is a central space of at least two-thirds of the diameter in which the definition is perfect, even in the smallest aperture of the eye-piece. Yet, for the purpose now referred to, I rarely use a field of much less than one minute in diameter; and any object not exceeding 45", when placed in the centre of the field and kept there by the driving-clock, is recognized with certainty under different powers, and seen with the utmost possible distinctness.

1. One of the objects I had principally in view was, to ascer

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Monthly Notices of the Royal Astronomical Society, May 13, 1864.

tain whether in any part of the photosphere any objects could be found which could reasonably be compared to "willow-leaves" (as called by Mr. Nasmyth) in their form.-It may be well to state here that I have always found it difficult to devise any appropriate appellation for the small bright irregularities of the surface, which would avoid an assumption of their character, or ascribe to them a regularity of form they do not possess. In my first paper I expressed my strong objection to any name of this kind, as calculated to convey an erroneous impression. The term willow-leaves seemed utterly inapplicable to anything I had ever succeeded in discovering. A far less objectionable term, as it appears to me, is that of rice-grains applied by Mr. Stone to those objects with which all careful Sun-observers must be acquainted, as there is no difficulty in seeing them in a moderately favorable state of the air, and which have been familiar to myself for many years;-so much so, indeed, that when they were not discernible I invariably abstained from any further scrutiny of the solar surface as being useless. Yet even this appellation conveys the idea of uniformity of shape and size which these objects do not possess, and is, I think, on that ground, objectionable. But I have been led by it to apply the term granulations, or granules, which assumes nothing either as to exact form or precise character; and I venture to hope that the term will be generally adopted.

To proceed then with the results of my recent observations. Various portions of the surface were diligently examined with powers from 131 to 407. The bright little granulations were easily seen in all parts not very near the edge of the disk. Their forms and sizes were carefully noted, and found to be so various as to defy every attempt to describe them by any one appellation or comparison. But, as I have observed in a former communication, the rarest of all forms was the long and narrow; and in no instance did I succeed in finding one which could with propriety be compared to a willow-leaf. Occasionally, some that were nearly in contact differed so greatly in size that one was four or five times as large as the other; and while, in a remarkably bright mass, one somewhat resembled a blunt and illshaped arrow-head, another, very much smaller and within 5" of it, was an irregular trapezium with rounded corners. The more quiet and perfect the views I obtained of them, the more convincing did the evidence appear that they were not individual and separate bodies of a peculiar nature, but only different conditions as to brightness or elevation of the larger masses forming the mottled surface; just as the brighter portions of that surface, and the faculæ also, are different conditions of the general photosphere, In these researches I met with nothing which had the slightest resemblance to the interlacing which Mr. Nas

myth has so clearly described and so distinctly depicted in his communication to the Manchester Literary and Philosophical Society; of which letter I was not aware when I penned my former paper on this subject. Mr. Nasmyth having subsequently favored me with a copy, I was so struck with the clearness and decision of his assertions that I began to think I must have overlooked the peculiar appearances of the objects which he has depicted in his diagram as being "the exact form of these remarkable structural details," which he describes as "forming the entire luminous surface of the Sun," and, therefore, to leave nothing untried, I collected all the information I could as to the means employed by him and by other observers who had seen something of the same kind, in the hope that some change in my apparatus or mode of using it might at length render me successful. Now, however, it appears that Mr. Nasmyth has withdrawn his former statements as to the exact and uniform figure of the objects he claimed to have discovered on the entire surface; and that, in fact, all that might have been regarded as a discovery resolves itself into an appearance perfectly well known many years before. The darker or shaded lines between the granules I distinctly observed in many places to be pretty thickly covered with dark dots, like stippling with a soft lead-pencil; and these are what have been called "pores" by Sir John Herschel, and "punctulations" by his father. Some of these were almost black, and looked like excessively small spots just breaking out. But none of them were seen to enlarge or materially alter their form, though at times so sharply defined with powers 276 and 407 that it was obvious they were in general not quite round.

It appears to me quite incomprehensible that, under such definition, any bright objects of peculiar form should have escaped detection when specially looked for; and I was certainly struck with the extreme rarity of a long and narrow shape among the hundreds of granules which I examined in those four days' observations. If therefore there are any willow-leafshaped objects to be seen, they must be quite distinct from these granulations, and can form no regular or usual ingredients in the composition of the solar surface.

On the penumbra of the spots then visible I found several long and narrow bright lines, extending like bits of white thread completely across the whole breadth of the penumbra without any break whatever; and, though there were several smaller pieces, not one of them would have suggested to my mind the comparison with a willow-leaf. Perhaps the bright granules of the general surface may sometimes be compressed into a longer form under the influence of the same forces which produce the longer threads or straws on the penumbra; but one of the most striking features of that part, as well as of the general surface, is,

according to my observations, the entire absence of uniformity in the brighter portions with respect both to their size and shape, 2. A second object of my investigations was to determine whether the granulations existed equally in the brightest and in the less luminous portions of the surface, which together form the general and comparatively coarse mottling of the photosphere.

On comparing together in the same field of view several of the more and less luminous masses which produce the coarse mottling of the surface, I came to the conclusion that the granules are generally larger as well as brighter on the brightest parts than on the darker; the difference in brightness of the individual granules in each part being much the same as in the different masses themselves. One fact struck me as very remarkable, that, on each of these larger masses, the individual granules are all very nearly of equal brilliance throughout the mass to which they belong. They are not in general, if ever, mixed together, some much brighter and others far less bright on the same mass. Occasionally I have noticed that some of the brighter masses are decidedly brighter than others of the same class, and that such have extended to a much greater length than usual. The granulations on them are also generally, I think, of uncommon size, and the shaded lines between them of a ligher tint. I strongly suspect that these specimens, if near the Sun's edge, would be seen as faculæ.

3. A third principal object I had in view was, to scrutinize especially the brighter parts immediately surrounding the penumbræ of spots (which in a former paper I have referred to as indicating a heaping up of the photosphere by some eruptive force proceeding from the centre of the spot), with the purpose of ascertaining whether the granulations elsewhere easily visible were to be found there; and also to examine the facula of various forms, sizes, and degrees of brightness, to determine whether any such granulations were visible upon them.

With reference to the reality of this brighter region surrounding all the considerable profound spots, and also some of the smaller ones, I have lately been much gratified by the corroboration of the fact afforded by some solar photographs taken by our President, and obligingly presented to me since the publication of my former paper. While the general mottling of the surface is well brought out in them, they show that this mottling never extends to the margins of the spots; which precisely agrees with my observations. In this locality I have never been able to detect any of the granulations so abundant and so easily seen elsewhere. My recent observations fully confirm the conclusion I have formerly arrived at, namely, that the commotion, of whatever kind it might be, had produced the effect of heaping up the material of the photosphere; and had confounded all

the distinctions elsewhere seen of the large brighter and shaded masses, and also of the granulations on both, and the pencillines, occasionally stippled, by which the individual granules are distinguished.

Precisely the same results attended my examinations of the facula. Nothing resembling granulations could be found on any of them, whether they were the tortuous, thread-like objects seen near the east and west borders, or the shorter lumps of apparently similar composition near the poles. Yet the granulations were discernible in several places nearer to the Sun's edge than the faculæ were situated; so that it could not arise from the obliquity of the view that they were not visible on the fac ulæ themselves. I conclude, therefore, that the same disturbance which produces the elevated ridges confuses the minute features elsewhere seen; and that, though there may be some traces of granulation when the faculæ are viewed almost perpendicularly, yet this is entirely lost when their sides only are seen near the Sun's limb. In this position, however, there are often distinct evidences of irregularity in the elevation of different parts of the ridge; and these may, perhaps, when viewed perpendicularly, produce variations of brightness, like the granules of extraordinary size mentioned above.

Hopefield Observatory, Haddenham, Bucks, May 9, 1864.

ART. XXII.-On Molecular Physics; by Prof. W. A. NORTON. [Continued from p. 78.]

IN considering the changes of state through which the same substance may pass, we have been led to recognize as an important physical principle upon which the mechanical properties manifested in each new condition in a great degree depend, that the physical condition of the individual molecules is liable to permanent variations from the effect of heat; and that these variations consist in expansions of the electric atmospheres which surround the atoms of the molecules. If we take a more extended view, and consider the diverse permanent changes of condition which the same substance may experience, while in the same state of aggregation, we may discern the operation of of a still more comprehensive principle; viz., that the physical state of the atmosphere of a molecule, and therefore the curve which represents its action upon surrounding molecules, is liable to permanent alteration from the action of external forces generally. It is well known that if a mechanical force, of considerable intensity, be applied for a short interval of time to a body, the result will be a permanent change in its form. The experiments of Hodgkinson have indeed established that a certain set may be imparted to bars of cast iron, by a temporary load