Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 27, 2025
Moreover, it is doubtful whether Eratosthenes made allowance, as he should have done, for the semi-diameter of the sun in measuring the angle of the shadow. But these are mere details, scarcely worthy of mention from our present stand-point. What perhaps is deserving of more attention is the fact that this epoch-making measurement of Eratosthenes may not have been the first one to be made.
Let the same things be supposed as before; that is to say, let CO, perpendicular to CR, represent a portion of a wave the continuation of which in the crystal is IK, so that the piece C will be continued on along the straight line CI, while O comes to K. Now if one takes a second period of time equal to the first, the piece K of the wave IK will, in this second period, have advanced along the straight line KB, equal and parallel to CI, because every piece of the wave CO, on arriving at the surface CK, ought to go on in the crystal the same as the piece C; and in this same time there will be formed in the air from the point I a partial spherical wave having a semi-diameter IA equal to KO, since KO has been traversed in an equal time.
And having regard to some other observations and phenomena of which I shall speak afterwards, I put N at 156,962 parts, of which the semi-diameter CG is found to contain 98,779, making this ratio 8 to 5-1/29.
From this it is to be noted that the proportion of the refraction for this section of the crystal is that of the line N to the semi-diameter CQ; by which one will easily find the refractions of all incident rays, in the same way as we have shown previously for the case of the section through FE; and the demonstration will be the same.
The question of the sun's distance arises naturally from the consideration of his temperature, since the intensity of the radiations emitted as compared with those received and measured, depends upon it. But the knowledge of that distance has a value quite apart from its connection with solar physics. The semi-diameter of the earth's orbit is our standard measure for the universe.
One might also determine the point C, and all the others, in this curve which serves for the refraction, by dividing DA at G in such a way that DG is 2/3 of DA, and describing from the centre B any arc CX which cuts BD at N, and another from the centre A with its semi-diameter AF equal to 3/2 of GX; or rather, having described, as before, the arc CX, it is only necessary to make DF equal to 3/2 of DX, and from-the centre A to strike the arc FC; for these two constructions, as may be easily known, come back to the first one which was shown before.
And now a surprise, the first I had encountered, awaited me. I registered the gravity as shown by the barycrite; and, extinguishing the electric lamp, measured repeatedly the semi-diameter of the Earth and of the halo around her upon the discometer, the inner edge of the latter affording the measurement of the black disc, which of itself, of course, cast no reflection.
It was on the N.N.W. side of the hill, so that I was sheltered from the heat every day, till it came to a W. and by S. sun, or thereabouts, which in those countries is near the setting. Before I set up my tent, I drew a half-circle before the hollow place, which took in about ten yards in its semi-diameter from the rock, and twenty yards in its diameter from its beginning and ending.
It was on the N.N.W. side of the hill, so that I was sheltered from the heat every day, till it came to a W. and by S. sun, or thereabouts, which in those countries is near the setting. Before I set up my tent, I drew a half-circle before the hollow place, which took in about ten yards in its semi-diameter from the rock, and twenty yards in its diameter, from its beginning and ending.
In measuring the error he perceived that the diameter of the sun's image was considerably short of twice the semi-diameter, a proof of the uncertainty of celestial observations made during these intense frosts. The results of this and another similar observation are given in the footnote.* The observed meridian altitude of sun upper limb was 2 degrees 52 minutes 51 seconds.
Word Of The Day
Others Looking