such as by firing gunpowder or gun-cotton; and, lastly, by a heated object throwing off heat. Taking the last first, it is impossible that the immense heat of the sun can result from his being an incandescent body. Every one knows how rapidly a red hot body cools at the surface. Look at a mass of iron taken from the furnace at a white heat, and in a short time its surface becomes black. The sun by radiation must long since have lost his heat. Can we fancy the heat of the sun to come from combustion? The ordinary process demands that it should be fed by air. We know the exact limits of the atmosphere of the sun, and even if it consisted of pure oxygen, it could not long uphold that enormous combustion. Suppose the sun made of gun-cotton, he would not have lasted 1,000 years. With the progress of physical science a new and startling theory has been promulgated, by which a key seems to be furnished to the mystery. Amongst the scientific men who have paid attention to this subject, I must mention a citizen of Manchester, a man of whom Manchester has reason to be proud, and who is one of our best and most accurate physical inquirers-Mr. Joule-who has led the way in this inquiry, and is worthy to rank with another of your illustrious sons-Dalton. By these inquiries we have been led nearer and nearer to what promises to be an intelligible and definite theory of heat. The science of heat is rapidly attaining a position quite as clear and satisfactory as the dynamical doctrine of gravitation itself.

One fact with regard to heat has long been understood, viz., its controvertibility into "mechanical effect." A certain quantity of heat will produce a certain amount of mechanical effect and no more, and it must produce that quantity in one form or another. A pound of coals burned will produce a definite mechanical effect, and you cannot make it produce more. Many improvers of the steam engine thought they could, and took out patents that certainly never

paid their expenses, by which they were going to make 1lb. of coals do what 10lbs. would not effect. This was well known for a long time; but the reverse of the proposition was not known-that a certain amount of mechanical effect, if destroyed, will reproduce itself in a definite amount of heat. You only seem to destroy it, for it instantly converts itself into its original form, viz., heat; and it produces exactly that quantity of heat which if consumed again would reproduce it. When a man rubs his hands to make them warm, the heat is evolved by the mechanical force he puts out. Look at the workman boring a hole in a piece of iron; there is a great deal of friction and a corresponding amount of heat; the axles of railway carriages are sometimes set on fire by friction. You cannot destroy mechanical effect; the effect that results is less than the power employed, but it passes off in friction, or heat. Not only mechanical effect, but all the other forces of the universe when impeded, evolve themselves into heat. You cannot destroy the slightest portion of a physical force; you may impede it, and it goes off in the form of heat. May we imagine the immense heat of the sun to arise from the expenditure of mechanical effect upon his surface, in other words, from the effect of bodies striking it? At first sight, the cause seems so inadequate that it may provoke a smile; but when dealing with phenomena so far beyond the range of ordinary experience, we must not give way to first impressions. I have said that meteoroids are abundant in the universe, and proceed with great velocity. Often they come within range of our earth, and sometimes strike it. I refer to what we call the "falling stars." They enter the earth's atmosphere at velocities varying from four to forty miles in a second, and consequently heat is evolved. If moving at a high velocity the stone becomes incandescent, and you see it as a bright body; if moving more swiftly the stone splits up like a rocket, from the tremendous heat evolved. Some

times the stones come to the earth entire, but in every case there are marks of great heat. This is the theory of the meteoroids, or falling stars. If you can fancy an enormous number of these always falling upon the earth, the upper part would become warm. As these meteoroids approach the sun, their velocity will necessarily immensely increase. A meteoroid that moves at the rate of about ten miles in a second on reaching the earth, will on approaching the sun move about 400 miles in a second. If the planet Mercury were ever to approach the sun, his velocity would be about 390 miles in a second. Now suppose that planet falling into the sun with such a velocity, what an enormous amount of mechanical effect would be destroyed, and precisely a proportionate amount of heat would be developed; we can tell by exact calculation, that it would be just as much as the sun radiates through space in three years! That enormous amount of heat would instantly flash through the whole of the interstellar space. The question isIs there such a mass of meteoroids round the sun falling in upon his surface? I know a speculation of this sort will look excessively strange at first, but to show you that it is not a fancy of my own, or of a few individuals, I may mention that it was one of the reasons for the despatch of an expedition at the instance of the British Association the other year, headed by Professor P. Smith, to the Peak of Teneriffe, to ascertain the existence of solar refraction, and to find if there was any accumulation of this matter in the neighbourhood of the sun, which could not be ascertained in our misty atmosphere. The existence of solar refraction is distinctly established; every star near the sun appears to be put out of its place, and the more so the nearer it is to the sun. It seems likely then that there is a vast mass of meteoroids falling regularly into the sun, and if so they must produce a corresponding amount of heat. They will not fall into the sun probably as solids, but the same

effects will be produced. What we call the spots on the sun, seem to be produced by the falling in of great quantities of this meteor dust. Much of what I am saying is conjectural, but if we wait with patience, in time there will be proof one way or the other; if the theory be true, there will be a perceptible increase of the size and heat of the sun in 150 years. There are myriads of suns besides our own, and proofs of change abound. There are multitudes of stars that have apparently changed their magnitude, and very often their colour, without changing their position; sometimes a star has been seen to blaze out suddenly, and afterwards to disappear. It is a fact that the whole of our system is necessarily approaching the sun, and in the course of time the whole of it, planets and all, will fall into his mass. The speculation therefore draws an additional illustration from this truth; it is not an exceptional case, ruling the meteoroids alone, but part of the general laws of our system. We fancy, at first sight, that our system is intended for everlasting duration, but we discover that it is only fitted for a long existence. We cannot attribute absolute stability to anything.

The lecturer expressed his belief that the zodiacal light is caused by a nebulous ring round the earth. This singular formation of rings was not an isolated phenomena. There were similar appendages round the planet Saturn. The existence of this curious peculiarity was first discovered by Galileo, but the truth regarding this phenomena we owe to Huyghens (1655). In 1665, an English astronomer named William Ball, who was possessed of a telescope of 38 feet focal length, made further discoveries respecting the structure of the ring. In 1789, Sir William Herschel began his superb series of observations. Laplace, as a dynamical or physical astronomer, not an observer, in the same year published some remarkable conjectures respecting the nature of the rings, reasoning from the laws of attraction, &c. About the same time

that he calculated these things, Sir William Herschel discovered them as matters of fact. The result of further discovery is, that we must give up the conception of the ring being solid. In 1850, a new ring was discovered. What are these rings? The lecturer gave his reasons for believing that they were masses, more or less dense, of asteroids that are known to exist in many parts of the solar system. The inner ring is getting nearer to the planet Saturn, and it is calculated that it will touch in about 150 years, when some curious phenomena may be expected.

IMPORTANCE OF OCCUPATION.-Not unfrequently have I heard women, who were surrounded by all the advantages that outward wealth can give, say, with sad and timid self-reproach, "I ought to be happy. It is my own fault that I am not. But, I know how it is, I cannot. get up an interest in anything." When I remind them that Richter said, "I have fire-proof perennial enjoyments, called employments," few have faith in such a cure for the inanity of life. But the only certain way to attain habitual content and cheerfulness, is by the active use of our faculties and feelings. Mrs. Somerville finds too much excitement and pleasure in her astronomical investigations, to need the poor stimulus of extravagant expenditure or gossipping about her neighbours. Yet the astronomer discharges all womanly duties with beautiful propriety. She takes nothing from her family.

She

merely gives to science those hours which many women in the same station waste in idleness and dissipation. What can be more charming than the example of Mrs. Huber, devoting herself to the study of natural history, to assist her blind husband in his observations? Or Mrs. Blake, making graceful drawings in her husband's studio, working off the impressions of his plates, and colouring them beautifully with her own hand?-Mrs. Child.