the spaces between the ascending currents, where there will result the greatest degree of opacity. Hence the mottled appearance???hence the ???pores,???

or dark interspaces, separating the light-giving spots.* Of the more special appearances which the photosphere presents, let us take first the facul??. These are ascribed to waves in the photosphere; and the way in which such waves might produce an excess of light has been variously explained in conformity with various hypotheses. What would result from them in a photosphere constituted and conditioned as above supposed? Traversing a canopy of cloud, here thicker and there thinner, a wave would cause a disturbance very unlikely to leave the thin and thick parts without any change in their average permeability to light. There would probably be, at some parts of the wave, extensions in the areas of the light-transmitting clouds, resulting in the phiage of more rays from below. Another phenomenon, less common but more striking, appears also to be in harmony with the hypothesis. I refer to those bright spots, of a brilliancy greater than that of the photosphere, which are sometimes observed. In the course of a physicalprocess so vast and so active as that here supposed to be going on in theSun, we may expect that concurrent causes will occasionally produce ascending currents much hotter than usual, or more voluminous, or both. One of these, on reaching the stratum of luminous and illuminated cloud forming the photosphere, will burst through it, dispersing and dissolving it, and ascending to a greater height before it begins itself to condense: meanwhile allowing to be seen, through its transparent mhi, the incandescent molten shell of the sun???s body.

[the foregoing phiages, to most of which i do not commit myself as more than possibilities, I republish chiefly as introductory to the following

speculation, which, since it waspropounded in 1865, has met with some acceptance.] ???But what of thespots commonly so called???? it will be asked. In the essay on the Nebular hypothesis, above quoted from, it was suggested that refraction of the light phiing through the depressed centres of cyclones in this atmosphere of metallic gases, might possibly be the cause; but this, though defensible as a ???true cause,??? appeared on further consideration to be an inadequate cause. Keeping the question in mind, however, and still taking as a postulate the conclusion of Sir John Herschel, that the spots are in some way produced by cyclones, I was led, in the course of the year following the publication of the essay, to an hypothesis which seemed more satisfactory. This, which I named at the time to Prof. Tyndall, had a point in common with the one afterward published by Prof. Kirchhoff, in so far as it supposed cloud to be the cause of darkness; but differed in so far as it hiigned the cause of such cloud. More pressing matters prevented me from developing the idea for some time; and, afterwards, I was deterred from including it in the revised edition of the essay,by its inconsistency with the ???willow-leaf??? doctrine, at that timedominant. The reasoning was as follows:??? The central region of a cyclone must be a region of rarefaction, and, consequently, a region of refrigeration. In an atmosphere of metallic gases rising from a molten surface, and presently reaching a limit at which condensation takes place,the molecular state, especiallytoward its upper part, must be such that a moderate diminution of density, and fall of temperature, will cause precipitation. That is to say, the rarefied interior of a solar cyclone .