Part 10 (2/2)
In this way, acting upon suggestions which had been thrown out previously to his own time by LAMBERT, MAYER, and BRADLEY, HERSCHEL deether with all its systeh space in an unknown and majestic orbit of its own The centre round which this ned We can only know the point in the heavens towards which our course is directed--”the apex of solar ned by MASKELYNE to the brighter stars, HERSCHEL was able to define the position of the solar apex with an astonishi+ng degree of accuracy His calculations have been several tie of modern analytical methods, and of the hundred-foldessential has been added to his results of 1805, which were based upon such scanty data; and his paper of 1782 contains the announcement of the discovery itself
His second paper on the _Direction_ and _Velocity_ of the solar systeiven of histhe heart of a matter, and it may be the one in which his philosophical powers appear in their highest exercise For sustained reflection and high philosophic thought it is to be ranked with the researches of NEWTON in the _Principia_
_Researches on the Construction of the Heavens_
HERSCHEL'S papers on the Construction of the Heavens, as he named it, extended over his whole scientific life By this he speciallyto which the stars, the clusters, the nebulae, are spread through the regions of space, the causes that have led to this distribution, and the laws to which it is subjected
No single astronoht which it may throw on the scheht As an instance: his discovery of the variable star _[alpha] Herculis_, which has a period of sixty days, was valuable in itself as adding one ht is now brighter, now fainter, in a regular and periodic order
But the chief value of the discovery was that noe had an instance of a periodic star which went through all its phases in sixty days, and connected, as it were, the stars of short periods (three to seven days) with those of very long ones (three hundred to five hundred days), which two groups had, until then, been the only ones known In the same way all his researches on the parallaxes of stars were not alone for the discovery of the distance of any one or two single stars, but to gain a unit of celestial ht be sounded
Astronomy in HERSCHEL'S day considered the bodies of the solar syste a cubical space
The ideas of near and far, of up and doere preserved, in regard to them, by common astronoht of, as they appear in fact to exist, lying on the surface of a hollow sphere The immediate followers of BRADLEY used these fixed stars as points of reference by which the motions within the solar systeathered those iues of their positions which are so indispensable to the science MIChell and HERSCHEL alone, in England, occupied their thoughts with the nature and construction of the heavens--the one in his study, the other through observation[34] They were concerned with all three of the dimensions of space
In his memoir of 1784, HERSCHEL says:
”Hitherto the sidereal heavens have, not inadequately for the purpose designed, been represented by the concave surface of a sphere, in the centre of which the eye of an observer ht be supposed to be placed
”It is true the various ested to us, and would have better suited, the idea of an expanded firmament of three di to enter still farther illustrate and enforce the necessity of considering the heavens in this point of view In future, therefore, we shall look upon those regions into which we e telescopes, as a naturalist regards a rich extent of ground or chain ofstrata variously inclined and directed, as well as consisting of very different lobe or map, therefore, will but ill delineate the interior parts of the heavens”
HERSCHEL'S method of study was founded on a _ It consisted in pointing a powerful telescope toward various parts of the heavens, and ascertaining by actual count how thick the stars were in each region His twenty-foot reflector was provided with such an eye-piece that, in looking into it, he saw a portion of the heavens about 15' in diameter A circle of this size on the celestial sphere has about one quarter the apparent surface of the sun, or of the full reater or less number of stars were visible These were counted, and the direction in which the telescope pointed was noted Gauges of this kind were made in all parts of the sky, and the results were tabulated in the order of right ascension
The following is an extract froe nuht ascension and north polar distance:
---------------------------------------------------------- | N P D || | N P D
R A | 78 to 80 || R A | 92 to 94
| No of Stars || | No of Stars
------------|-----------------||-----------|-------------- H M | || H M | 11 6 | 31 || 15 10 | 94 12 31 | 34 || 15 22 | 106 12 44 | 46 || 15 47 | 106 12 49 | 39 || 16 8 | 121 13 5 | 38 || 16 25 | 136 14 30 | 36 || 16 37 | 186 ----------------------------------------------------------
In this s or of distribution obtains in the two regions Such differences are still more marked, if we compare the extreme cases found by HERSCHEL, as R A = 19h 41m, N P D = 74 33', number of stars per field = 588; and R A = 16h 10m, N P D = 113 4', number of stars = 11
The nureat For example, in the Milky Way, near _Orion_, six fields of view proave 110, 60, 70, 90, 70, and 74 stars each, or a mean of 79 stars per field
The ave 60 stars So that as HERSCHEL'S sweeps were two degrees wide in declination, in one hour (15) there would pass through the field of his telescope 40,000 or reat as 116,000 stars in a quarter of an hour
When HERSCHEL first applied his telescope to the Milky Way, he believed that it completely resolved the whole whitish appearance into small stars This conclusion he subsequently reat stratum called the Milky Way is that in which the sun is placed, though perhaps not in the very centre of its thickness
”We gather this from the appearance of the Galaxy, which seems to encompass the whole heavens, as it certainly must do if the sun is within it For, suppose a nued between two parallel planes, indefinitely extended every way, but at a given considerable distance fro this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratureat circle, which will appear lucid on account of the accumulation of the stars, while the rest of the heavens, at the sides, will only seem to be scattered over with constellations,to the distance of the planes, or number of stars contained in the thickness or sides of the stratum
”If the eye were placed soreat distance, the appearance of the stars within it would assume the form of one of the smaller circles of the sphere, which would beto the distance of the eye; and, if this distance were exceedingly increased, the whole stratuether into a lucid spot of any shape, according to the length, breadth, and height of the stratum
”Suppose that a smaller stratum should branch out from the former in a certain direction, and that it also is contained between two parallel planes, so that the eye is contained within the great stratum somewhere before the separation, and not far from the place where the strata are still united Then this second stratuht circle like the for froain at a distance less than a se surfaces are not parallel planes, but irregularly curved surfaces, analogous appearances must result”
The Milky Way, as we see it, presents the aspect which has been just accounted for, in its general appearance of a girdle around the heavens and in its bifurcation at a certain point, and HERSCHEL'S explanation of this appearance, as just given, has never been seriously questioned One doubtful point reh space? or are they near its bounding planes, or clustered in any ithin this space so as to produce the same result to the eye as if uniformly distributed?
HERSCHEL assuh the space in question He only exa of stars surrounding the sun, and he pronounced against such an arrange in the size or brilliancy of the sun to cause us to suppose it to be the centre of such a gigantic system No reason, except its ied for such a supposition Every star will have its own appearance of a Galaxy or Milky Way, which will vary according to the situation of the star