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The observations which he made upon it, and the speculations which they suggested, formed the subject of three lectures, the beginning of the first of which only has reached our times. From the absence of parallax, he proved that the common hypothesis of its being a meteor was erroneous, and that, like the fixed stars, it was situated far beyond the bounds of our own system.
Sir William Herschel began his observations of double stars in the hope of discovering an annual parallax of the stars. In this he was following a suggestion of Galileo's. The presumption is that, if there be no physical connection between the stars of a pair, the largest is the nearest, and has the greatest parallax.
A second campaign in stellar parallax was undertaken by Gill and Elkin in 1887. But this time the two observers were in opposite hemispheres. Both used heliometers. Dr. Elkin had charge of the fine instrument then recently erected in Yale College Observatory; Sir David Gill employed one of seven inches, just constructed under his directions, in first-rate style, by the Repsolds of Hamburg. Dr.
A sermon by a lay-preacher may be worth listening I replied, calmly. It gives the parallax of thought and feeling as they appear to the observers from two very different points of view. If you wish to get the distance of a heavenly body, you know that you must take two observations from remote points of the earth's orbit, in midsummer and midwinter, for instance.
There is a terrible parallax between the period before thirty and that after threescore and ten, as two men of those ages look, one with naked eyes, one through his spectacles, at the man of fifty and thereabout. Magendie, I doubt not you have all heard of. I attended but one of his lectures.
Astr. Cél., found by Argelander to have a proper motion of 4·734", and by Winnecke a parallax of O·511". Month. [Footnote 79: Mém. Prés.
In the course of his investigation of sidereal parallax, though without finding it, Herschel made an important discovery; that of the proper motion of our system. To show distinctly the direction of the motion of the solar system, not only was a displacement of the sidereal perspective required, but profound mathematical knowledge, and a peculiar tact.
He remarked that the error of this determination did not amount to one twentieth of the whole, whence it followed that the true value of the parallax could not exceed 8".2. Laplace, by an analogous process, determined the parallax to be 8".45. Encke, by a profound discussion of the observations of the transits of Venus in 1761 and 1769, found the value of the same element to be 8".5776.
An object-glass for which he had furnished the material to Cauchoix, procured him, in 1823, a royal invitation to settle in Paris; but he was no longer equal to the change, and died at the scene of his labours, February 13 following. Bequeathed by South to Trinity College, Dublin, it was employed at the Dunsink Observatory by Brünnow and Ball in their investigations of stellar parallax.
But we know for certain that the distance of none of these visible stars, without a measurable parallax, is less than four million times the distance of our sun from the earth. It would be useless to express this in figures as it would be altogether incomprehensible. What then can be said of the telescopic stars, not to speak at all of those beyond the power of instruments to determine.
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