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I found I could survey the river as we proceeded by measuring, with a pocket sextant, the angle subtended by the two ends of a twelve feet rod held in the second boat, at the opposite end of each reach, the bearing being observed at the same time. By referring to one of Brewster's tables, the angle formed by the rod of twelve feet, I ascertained thus the length of each reach.
In the meantime, Gascoigne had been measuring an equilateral triangle of twelve paces and marked it out. Mr Tallboys, on his return with the purser's steward, went over the ground, and finding that it was "equal angles subtended by equal sides," declared that it was all right.
The arc subtended in the sky by the moon is a fifteenth part of a sign" of the zodiac; that is to say, since there are twenty-four, signs in the zodiac, one-fifteenth of one twenty-fourth, or in modern terminology, one degree of arc. This is Aristarchus's measurement of the moon to which we have already referred when speaking of the measurements of Archimedes.
"But," objected Butler, "when you have taken all those angles you will have done only part of the work; you will still have to calculate the length of the vertical and horizontal lines subtended by them " "A matter of about half an hour's work!" interjected Harry. "Possibly," agreed Butler.
Wild sweeps of fell and field faded on the sight to those dim and remote hues of distance only visible upon days of exceeding aerial brilliancy. Immediately beneath the eminence subtended ragged expanses of rainbow-colored heath and fern and furze spotted with small fir trees which showed blue against the tones of the moor.
He knew what they were, and his spine crawled at the thought of what would happen if the Huks found out. But the distant objects were at the limit of certain range for detection devices. The planet's instruments could just barely pick them up. They subtended so small a fraction of a thousandth of a second of arc that no information could be had about them.
Great decrease in the earth's apparent diameter, which now subtended from the balloon an angle of very little more than twenty-five degrees. The moon could not be seen at all, being nearly in my zenith. I still continued in the plane of the elipse, but made little progress to the eastward. "April 14th. Extremely rapid decrease in the diameter of the earth.
The parallax of the sun is the angle subtended by the earth's radius at the sun's distance. A. R. Hinks, R.A.S.; Monthly Notices, June, 1909. Ph. The writer considers that it is more likely that these notes refer to a kind of camera obscura, in which a lens throws an inverted image of a landscape on the wall.
The angle was never smaller than 2' 17"; therefore at its maximum it was about one fourteenth of the angle subtended by the diameter of the moon. Herschel did not say, either of what nature the circles and squares of paper were that he used, nor on what background they were projected. It is a lacuna to be regretted, for in those phenomena the intensity of light must be an important feature.
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