These vast cavities then in the sun we call spots are not solid things, and not properly to be compared even to masses of slag or scoria swimming on a molten surface. They are rather rents in that bright cloud surface of the sun which we call the photosphere, and through which we look down to lower regions. Their shape may be very rudely likened to a funnel with sides at first slowly sloping (the _penumbra_), and then suddenly going down into the central darkness (the _umbra_). This central darkness has itself gradations of shade, and cloud forms may be seen there obscurely glowing with a reddish tinge far down its depths, but we never see to any solid bottom, and the hypothesis of a habitable sun far within the hot surface, suggested by Sir William Herschel, is now utterly abandoned. We are able now to explain in part that mysterious feature in the sun's rotation before insisted on, for if the sun be not a solid or a liquid, but a mass of glowing vapor, it is evidently possible that one part of it may turn faster than another. _Why_ it so turns, we repeat, no one knows, but the fact that it does is now seen to bear the strongest testimony to the probable gaseous form of the sun throughout its mass--at any rate, to the gaseous or vaporous nature of everything we see. We must not forget, however, that under such enormous temperature and pressure as prevail there the conditions may be--in fact, must be--very different from any familiar to us here, so that when we speak of "clouds," and use like expressions, we are to be understood as implying rather an analogy than an exact resemblance. [Illustration: Fig. 12] We must expect, with the great advances photography has lately made, to know more of this part of our subject (which we may call solar meteorology) at the next spot maximum than ever before, and by that time it may be hoped that some of the wonderful forms described above so imperfectly will have been caught for us by the camera. * For parts 1 and 2 see SCIENTIFIC AMERICAN for July 20 and July 27. * * * * * IN the notice in our issue for July 27 of a new screw cutting lathe made by Messrs. Goodnow & Wightman, the address should have been 176 Washington street instead of 128, and the diameter of the tail spindle, which was given as 5/16, should have been 15/16 inch. * * * * * THE Olympia (Wyoming Territory) _Standard_ announces that a company has been formed there to bring ice from a glacier. The deposit covers a number of acres, is seventy or eighty feet deep, and is supposed to contain a hundred thousand or more tons, some of which may have been there as many years. The ice can be cut and sold at one and one half cents a pound, and by the ship load at five dollars a ton. * * * * * =MECHANICAL PUDDLING IN SWEDEN.=