By Sir John Frederick William Herschel
Astronomer and thinker Sir John Herschel (1792-1871), the son of William and the nephew of Caroline, released his 1833 Treatise on Astronomy within the 'Cabinet Cyclopaedia' sequence of which the 1st quantity have been his drastically profitable initial Discourse at the examine of ordinary Philosophy. he's considered as the founding father of the philosophy of technology, and made contributions in lots of fields together with arithmetic, the newly found strategy of images, and the botany of southern Africa, which he studied whereas making astronomical observations of the southern hemisphere, and the place he was once visited via Darwin and Fitzroy at the Beagle voyage. It was once although because the normal successor to his father's astronomical experiences that he's most sensible remembered, and this e-book, that's written for the lay individual, locations robust emphasis at the value of exact statement and on keeping off preconceptions or hypotheses now not in line with such commentary.
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Extra resources for A Treatise on Astronomy
It is the angular breadth of this redundant zone — the angle Y MQ, "by which the visible horizon appeai-s de* See this instrument described in Chap. II, CHAP. I. EFFECT OF THE E A R T H ' S CURVATURE. 19 pressed below the direction of a spirit-level—that is called the dip of the horizon. It is a correction of constant use in nautical astronomy. ) From the foregoing explanations it appears, 1st, That the general figure of the earth (so far as it can be gathered from this kind of observation) is that of a sphere or globe.
Tion, which seems to revolve with a uniform motion, as if it formed one coherent mass; or as if it were attached to the internal surface of a vast hollow sphere, having the earth, or rather the spectator, in its centre, and turning round an axis inclined to his horizon, so as to pass through that fixed point or pole already mentioned. ( 6 l . ) Lastly, he will notice, if he have patience to outwatch a long winter's night, commencing at the earliest moment when the stars appear, and continuing till morning twilight, that those stars which he observed setting in the west have again risen in the east, while those which were rising when he first began to notice them have completed their course, and are now set; and that thus the hemisphere, or a great part of it, which was then above, is now beneath him, and its place supplied by that which was at first under his feet, which he will thus discover to be no less copiously furnished with stars than the other, and bespangled with groups no less permanent and distinctly recognizable.
17 M Q q, the point of contact N will mark out on the surface the circle N O P Q . The area of this circle is the portion of the earth's surface visible to a spectator at Mj and the angle N M Q included between the two extreme visual rays is the measure of its apparent angular diameter. Leaving, at present, out of consideration the effect of refraction in the air below M, of which more hereafter, and which always tends, in some degree, to increase that angle, or render it more obtuse, this is the angle measured by the dip sector.