It has been inferred from measuring the barometrical pressure at different elevations, that the earth’s atmosphere extends to the height of 40 miles, beyond which limit we are left to conjectures, founded on the supposed divisibility of matter; which, if infinite, indicates an infinity of atmosphere. If, however, it consist of ultimate indivisible particles, then expansion of the medium composed of them must cease at that point where the force of gravity downwards, upon a single particle, is equal to the resistance arising from the repulsive force of the medium. If we adopt the latter hypothesis, no part of our atmosphere could ever leave the earth; if the former, every planetary body must possess its respective share, provided we rest our reasoning upon the known properties of matter. The author, therefore, thought it deserving of consideration, whether, in any instance, any deficiency of atmosphere could be proved, and whether, from such source, any conclusive argument could be drawn in favour of ultimate atoms of matter in general; for since the chemical law of definite proportions applies to all forms of matter, if it can be proved that any one body consists of particles no longer divisible, we then can scarcely doubt that all others are similarly constituted. In respect to the non-existence of an atmosphere round the moon, Dr. Wollaston observes, that the quantity of such matter retainable by a body of the moon’s magnitude, could not give rise to any phenomena observable by our instruments; that we should therefore look for information in an opposite direction, and examine that body which has the greatest power; if we there find no appearance of an atmosphere, we may infer that our own is peculiar to the earth. In respect to the sun, for instance, if we calculate at what apparent distance from his body his force is equal to that of gravity at the surface of the earth, it is there that his power would be sufficient to accumulate, from an infinitely divisible medium filling all space, an atmosphere fully equal in density to our own, and therefore producing a refraction of more than 1° in the passage of rays obliquely through it. Dr. Wollaston then proceeds to show, from a detail of observations of the passage of Venus near the sun in superior conjunction, which took place in May last, that no such retardation in the motion of that planet could be perceived in her progress toward the sun, as would occur from increasing refraction, and that the phenomenon does not offer the least evidence of the existence of a solar atmosphere.
VII. An Improvement of the Method of correcting the Observed Distance of the Moon from the Sun or a Fixed Star
