Page:Proceedings of the Royal Society of London Vol 1.djvu/201

Rh absorb its luminous particles, in a manner nearly similar to that which Dr. Herschel has supposed to take place with regard to the sun's atmosphere.

4thly. That as the variable star in Sobieski’s Shield is occasionally diminished in appearance to the 6th or 7th magnitude, or even to a smaller magnitude, it appears that these luminous particles are but sparingly dispersed in its atmosphere.

- 5thly. He asks, may we not with much plausibility represent such luminous particles as spots, somewhat circular, and of no great ex- tent.

Gthly. That the principal bright parts are but slight patches, may, he says, be presumed, from the perpetual changes they undergo, and also from such changes being very visible to us. -

7thly. He thinks we may obtain some idea of the relative situation or intervals between these bright parts, by the observations of the increase and decrease of brightness, as thereby the changes and times elapsed are pointed out.

Mr. Pigott says he has tried, practically, the effect of the above suppositions, by placing small white spots on a dark sphere, which sphere being turned round, represented the various changes as nearly as could be expected. Of these changes several views are given, ac- companied with some observations on variable stars in general ; in the course of which the author supposes it probable that many stars have lost their light, and that there are many others which have never shown a glimpse of brightness. He even asks, whether we may not suppose the number of these unenlightened stars equal to that of those endowed with light? If so, he thinks that by being collected together in clusters, as in the Milky Way. they must intercept all more distant rays; and if free from any intervening lights, must ap- pear as dark spaces in the heavens, similar to what has been observed in the southern hemisphere.

Mr. Pigott, at the conclusion of his paper, says he thinks there are strong reasons to believe that the sun’s luminous appearance has been at times considerably diminished; also, that he has little hesitation in conceiving it may, at some future period, be reduced to small patches. -

The mineral. of which an account is here given by Mr. Davy, was found many years ago by Dr. Wavel, in a quarry near Bamstaple. It was then considered as a kind of zeolite; but Mr. Hatchett, who visited the place in the year 1796, describes it as ﬁlling some cavities and veins in a rock of soft argillaceous schistns; and from that cir- cumstance concluded, that it most probably did not belong to the