Comer's navigation simplified; A manual of instruction in navigation as practised at sea. Adapted to the wants of the sailor. Containing all the tables, explanations, and illustrations necessary for the easy understanding and use of the practical branches - Softcover
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1868 Excerpt: ... sun ever can; also it can, and always will, be north a part of each lunar month, and the other part south. It must be seen which it is, when taken from the Almanac. The moon being much nearer the earth than the sun, the effect of parallax is very much greater, which makes a larger correction for the altitude. The sun is 95,000,000 miles distant, and its parallax is only a few seconds at most; and in observations taken at sea for latitude, to the nearest minute only, it may be wholly neglected, as was done in the cases just given. But the moon is on an average of only about 239,000 miles distant from it; although its distance varies considerably, and its parallax varies with its distance, it being 61J' nearly, when the moon is nearest, and less than 54' when it is farthest off. Ih Table VIII., page 22, we have given the correction for semidiameter, dip, parallax, and refraction, to be added to the apparent altitude of the moon if the lower limb is observed; and at page 23, the correction to be applied to the apparent altitude of the moon if the upper limb is observed. In the construction of this table, 4' have been allowed for dip; thus if the height of the eye above the water is considerably more or less than 17 feet, or if an artificial horizon is used, allowance must be made for this as described in the Explanation of the Tables. CASK II. To find the correction from the table, we must first obtain the moon's horizontal parallax for the time we took the observation. The moon's horizontal parallax is given in the American Nautical Almanac for noon and midnight; and the difference for one hour, which is given in the next column, needs only be multiplied by the number of hours past noon or midnight at Greenwich, and applied by addition when increasing, or su...
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