1680, one hundred and twelve millions of miles beyond the nucleus of that body?

126. If matter is projected from the sun to the remote regions of the solar system, and is arrested there, will the matter at rest be upheld because of the impact upon it of the matter in motion? but as the matter collected at the outskirts of the solar system increases in density, and, therefore, diminishes in magnitude, the impact upon it of the matter projected from the sun will be always the less, and, therefore, the matter in process of condensation will, because of this, approach nearer and nearer to the sun?

127. If matter is projected from the sun to the remote regions of the solar system, and impinges upon the planetary bodies, the planets are, therefore, acted upon by two forces-by gravity, which impels. them in a direction towards the sun, and by the matter projected from that body, which impels them in an opposite direction. Are these two forces, at the mean distance of a planet from the sun, in a state of equilibrium?

128. If so, the mass and diameter of a planet being given, to find the position of that planet in the solar system.

It is possible that the masses of all the planetary

bodies may not yet be accurately determined, as it would appear that Encke's comet has recently led to a determination of a smaller mass for the planet Mercury.

129. Has the ocean of the planet Venus evaporated consequent upon its proximity to the sun? and because of this, is the apparent disc of that planet enlarged?

130. If the density of the planet Venus could be determined apart from the atmosphere which surrounds it, would it be found that the density of the solid mass of Venus is greater than that of the Earth?

131. If the densities of the planets could be respectively determined apart from the water and atmosphere which surround them, would it be found that the density of the solid mass of a planet is always the greater according to the proximity of that planet to the sun?

132. In place of a nebula, according to the nebular hypothesis, giving birth to a star, is it so, that every star gives birth to a nebula or cluster of stars?

133. Are the unresolved nebulæ or clusters of stars, Figs. 18, 19, 20, the products of the visible stars with which each is associated?

134. Is the reticulated unresolved nebula, Fig. 21, the product of the visible stars with which it is associated?

135. Sir John Herschel has noticed, in the London Philosophical Transactions for 1833, "that he has

often seen, when the sky is quite clear, all the large stars above the seventh magnitude surrounded with photospheres of 2' or 3′ or more in diameter, precisely resembling that about the finer specimens of nebulous stars." Do these photospheres consist of luminous points or stars, though yet unresolvable by our best telescopes, each photosphere being a portion of that firmament of stars to which, as we suppose, each star or system of stars is destined to give birth?

136. If the planets cease not to increase in density, will they at length become incandescent?

137. Do self-luminous stars within determinate distances repel each other? but beyond those distances, have they a tendency to gravitate toward

each other?

And is it because of these antagonist

forces, that stars are found associated together in clusters, and not concentrated into one self-luminous or incandescent mass?

138. In the remote past, has our sun given birth to numerous planetary bodies, which have become self-luminous, and which are now observable as nebulous matter in the distant regions of the solar system?

139. What is the zodiacal light? Is it analogous to those photospheres which have been observed by Sir John Herschel as surrounding the larger stars of our firmament; but which, though yet unresolvable by our best telescopes, is a portion of that firmament of stars to which the sun, as we suppose, is destined to give birth?

From late observations upon the zodiacal light, it would seem that the light is only upon one side of the sun, and if seen from a distant point of view in space, would it, with the sun, present somewhat the appearance of the nebulæ, Fig. 22?

140. Shall the Earth, if burned up, and the planets in their turn, become each the parent of a planetary system; and thus there shall be the creation of suns, and worlds, and systems in never-ending succession?