Part 10 (1/2)

In the introduction to his paper on the _Nature and Construction of the Sun and Fixed Stars_ (1795), HERSCHEL recounts as known of the nature of the sun at that time NEWTON had shown that it was the centre of the system; GALILEO and his successors had determined its rotation, the place of its equator, its real diaravity on its surface He says:

”I should not wonder if, considering all this, ere induced to think that nothing reard to the internal construction of the sun” ”The spots have been supposed to be solid bodies, the s on an ocean of fluid s” ”The sun itself has been called a globe of fire, though, perhaps, metaphorically” ”It is time now to profit by the observations we are in possession of

I have availedastronomers, but have been induced thereto by my own actual observation of the solar phenomena”

HERSCHEL then refers to the theories advanced by his friend, Prof

WILSON, of Glasgow, in 1774 WILSON maintained that the spots were depressions below the sun's atmosphere, vast hollows as it were, at the bases of which the true surface of the sun could be seen

The essence of his theory was the existence of two different kinds of matter in the sun: one solid and non-luaseous and incandescent--the atmosphere Vacant places in the atmosphere, however caused, would show the black surface of the solid iven of the _faculae_, bright streaks, which appear on the sun's surface from time to time; but his theory accounted for the existence of the black _nuclei_ of the spots, and for the existence of the _penumbrae_ about these The penumbra of a spot was formed by the thinner parts of the atmosphere about the vacancy which surrounded the nucleus

This theory of WILSON'S was adopted by HERSCHEL as a basis for his own, and he brought numerous observations to confirave to it

According to HERSCHEL, the sun consisted of three essentially different parts First, there was a solid nucleus, non-lu inhabited Second, above this was an atmosphere proper; and, lastly, outside of this was a layer in which floated the clouds, or bodies which gave to the solar surface its intense brilliancy:

”According to my theory, a dark spot in the sun is a place in its atmosphere which happens to be free from luminous decompositions”

above it

The two at thickness about a spot, will account for all the shades of darkness seen in the penu currents froions, and ive rise to faculae, which HERSCHEL shows to be elevated above the general surface

It will not be necessary to give a further account of this theory The data in the possession of the modern theorist is a thousand-fold that to be derived from HERSCHEL'S observations, and, while the subject of the internal construction of the sun is to-day unsettled, we know that many important, even fundamental, portions of his theory are untenable

A rereat part in such theories:

”That the eht must waste the sun, is not a difficulty that can be opposed to our hypothesis Many of the operations of Nature are carried on in her great laboratory which we cannot comprehend Perhaps the many telescopic comets ht”

Arguments in favor of the habitability of both sun and moon are contained in this paper; but they rest more on a metaphysical than a scientific basis, and are to-day justly forgotten

_Researches on the Motion of the Sun and of the Solar Systeard to some of his discoveries of double stars:

”These may serve another very in to nitude have been observed or suspected to have a proper motion; hence we may surmise that our sun, with all its planets and comets, may also have a motion towards some particular point of the heavensIf this surmise should have any foundation, it will show itself in a series of soe, due to the motion of the whole solar system”

In 1783 he published his paper _On the Proper Motion of the Solar System_, which contained the proofs of his surmises of a year before

That certain of the stars had in fact a _proper_ hteenth century After all allowances had been made for the effects of precession and other displacements of a star's position which were produced by motions of the earth, it was found that there were still s differences which must be due to the motion of the star itself--its proper motion

The quantity of this motion was not well known for any star when HERSCHEL'S researches began Before they were concluded, however, MASKELYNE had deduced the proper motions of thirty-six stars--the fundamental stars, so called--which included in their nuhtest stars

It is _a priori_ evident that stars, in general, must have proper ravitation That any fixed star should be entirely at rest would require that the attractions on all sides of it should be exactly balanced Any change in the position of this star would break up this balance, and thus, in general, it follows that stars must be in motion, since all of them cannot occupy such a critical position as has to be assumed If but one fixed star is in motion, this affects all the rest, and we cannot doubt but that every star, our sun included, is in reat If the sun alone had a motion, and the other stars were at rest, the consequence of this would be that all the fixed stars would appear to be retreating _en masse_ fro Those nearest us would move more rapidly, those more distant less so And in the sa would see each other

If the stars, instead of being quite at rest, as just supposed, had motions proper to themselves, then we should have a double complexity

They would still appear to an observer in the solar system to have motions, and part of these motions would be truly proper to the stars, and part would be due to the advance of the sun itself in space

Observations can show us only the _resultant_ of these twoto separate this resultant into its two components

At first the question is to determine whether the results of observation indicate any solar motion at all If there is none, the properall possible lines If the sun does truly reement in the resultantwhich it moves, while those at the sides, so to speak, will show comparatively less syste in the rear of a railway train and watching the rails over which it has just passed As we recede from any point, the rails at that point seeether

If ere passing through a forest, we should see the trunks of the trees froether, while those on the sides of us would rerow further and further apart

These phenomena, which occur in a case where we are sensible of our own motion, serve to shoe may deduce a motion, otherwise unknown, from the appearances which are presented by the stars in space