INTRODUCTION,

xxiii

they owed their combustibility, and that combustion was nothingmore than a separation of this principle, gave rise to the phlogis-tic or Stahlian theory, which was afterwards modified by Dr,

rather of lucid decompositions taking' place within that atmosphere. ThePhilosophical Transactions , 1795, p. 72, also contains remarks on thislucid matter. Having rejected the old terms of spots, nuclei, penumbra:,and luculi, he has substituted those of openings, shallows, ridges, nodules,corrugations, indentations, and pores. The openings are places where theluminous solar clouds are removed, which he thinks are produced by awind or gas from the sun’s body. Shallows are depressions below the lu-minous clouds, and are caused by the propelling gas, which produces theopenings. They are tufted like masses of clouds. Ridges are elevations ofthe luminous clouds. The length of one of the longest was found to be75,000 miles. They generally surround the openings. Herschel thinks itprobable, from appearances, that the luminous matter is disturbed at topby the transparent elastic fluid, which issues from the openings. Nodulesare small elevations of the luminous matter. Corrugations are smallerelevations and depressions of the same matter. Indentations are the darkplaces of corrugations. That they are not much depressed, is deducedfrom their visibility near the margin of the sun. They are of the same na-ture as shallows, and of different sizes. Pores are the low places of inden-tations. The doctor is of opinion, that the phenomena before describedcould not appear, if the shining matter were a liquid; because, by the lawsof hydrostatics, the openings, shallows, indentations, and pores would befilled up. Still less could these phenomena exist with the supposition ofelastic fluidity The shining matter, he concludes, must exist in the man-ner of empyreal luminous or phosphoric clouds. The planetary atmosphereof the sun, its great height, its density, as inferred from the power of gra-vitation, which is known to be twenty-seven times stronger at the sun’ssurface than with us, and other subjects are also discussed. He supposesthe gas to pass from the sun itself upwards to the region of the clouds, soas to generate pores, corrugations, &c. He concludes finally, that if thisview of the solar appearances be well founded, there will be no difficultyin ascertaining the actual state of the sun with regard to its energy in giv-ing heat and light.

Inapaperon the “ Construction of the Heavens,” the doctor thinks it pro-bable, that the great stratum called the milky way is that in which the sunis placed, though perhaps not in the centre of its thickness. The celebrat-ed astronomer Lalande supposes the spots before mentioned to be parts ofthe solid body of the sun, but admits not a luminous atmosphere, but a lu-minous ocean. For the observations of Dr. Young, see his Natural Phi­ losophy , and of sir Isaac Neivton, his Principia, &c. Consult also Biot.