The animals, either wholly new, or new to Britain, described in the following communication, were taken during a yachting cruise, with our indefatigable friend Mr Macandrew, among the Hebrides, in the month of August 1850. During this voyage, which lasted three weeks, a series of observations were conducted by means of the dredge and the towing-net. Not a single new form of testaceous mollusk was procured; our exertions were amply rewarded, however, by the discovery of several remarkable Ascidians and Radiata, some of them so curious in themselves, and so important in their zoological bearings, that we have thought it desirable to lay an account of their characters and anatomy before the Royal Society of Edinburgh.

In the first part of this paper, I have endeavoured to prove, that the red prominences seen during total solar eclipses, exist in the sun; and I now propose to state some views which have occurred to me as to the nature of those remarkable objects, and their possible connexion with other solar phenomena. It is not, however, without great misgivings that I venture on this subject; for we know so little of the sun, that any hypothesis regarding the constitution of his atmosphere, can amount only to a conjecture, possessing more or less probability according to the variety of the appearances it serves to explain, and the exactness with which theory and observation correspond in each case: and I am well aware that views which may seem probable to myself may not appear equally so to others, whose greater experience in observing the sun constitutes them better judges of such questions.

81. A body which is either emitting heat, or altering its dimensions against resisting forces, is doing work upon matter external to it. The mechanical effect of this work, in one case, is the excitation of thermal motions, and in the other, the overcoming of resistances. The body must itself be altering in its circumstances, so as to contain a less store of work within it, by an amount precisely equal to the aggregate value of the mechanical effects produced: and conversely, the aggregate value of the mechanical effects produced, must depend solely on the initial and final states of the body, and is therefore the same, whatever be the intermediate states through which the body passes, provided the initial and final states be the same.

In several communications made to this Society and to the British Association, I have announced the results of a series of observations on the distribution of Fluorine throughout the mineral, vegetable, and animal kingdoms. To myself, the least satisfactory part of these investigations has been the inquiry into the presence of fluorine in plants, for I have been more frequently foiled than successful in my attempts to detect it in them. Others have not, apparently, been more successful. Daubeny was as unable as Sprengel at an earlier period had been, to obtain evidence that the element under notice is present in vegetable structures; and Will of Giessen, the discoverer of fluorine in plants, speaks only of “traces” of it having been detected in barley. Later observers have not spoken more confidently concerning its abundance in vegetables; and in the many analyses of the ashes of plants which have recently been published, it seldom, if ever, finds a place.

When preparing to make a night journey over one of the plains of South Africa, in the month of June 1843, a friend called my attention to the peculiar appearance of the sky in the west, as offering a very decided proof, “agreeably with theory,” that there was no “Solar atmosphere” to be seen at that season of the year.

On looking in the direction mentioned, the last portion of the twilight was just visible, and forming a peculiarly level line above the place where the sun had set, for an extent in azimuth, of perhaps 40°, and at a height of about 5°. All the gorgeous colours which had attended the setting of the sun had long since vanished, and there only remained sufficient light within the flattened arc described, to make the space included between it and the horizon appear light blue, while all the rest of the sky had attained a deeper colour, nay was almost black, and thickly spangled with small as well as large stars.

Eclipses are still, as they have ever been, very important phenomena for the astronomical observer; partly on account of the crucial test which they afford for the examination of the truth of the theory and calculation of the motions, real and apparent, of the Sun and Moon, partly also for the special opportunities which they furnish of inquiring into some of the arcana of the physical characteristics of those bodies.

For the former purpose, a partial eclipse will serve almost as well as a total one; while the continued improvement of the observation of meridian passages is now raising these daily measures fully to the importance of the other occasional phenomena, as a test of the theory. But for inquiry into the physics of the Sun, a perfectly total eclipse of that body is necessary; revelations may then happily be procured, which no observation of any other phenomena at any other time, can hope to afford any suspicion of.