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138 the motion was of one star round a companion star, or round some far greater and immensely more distant sun.

The conclusion which Herschel arrived at was that the whole solar system was at that time moving towards the constellation Hercules in the northern sky, and that the star "λ Herculis is possibly as well chosen as any we can fix upon in that part of the heavens" for the point we are moving towards. He modified this view in 1804 on receiving more correct measurements from the Astronomer-Royal: "It will be necessary to mention that I have no longer supposed the solar motion to be directed towards λ Herculis. A point at no very great distance from this star has been chosen." As the direction of the tangent to the sun's orbit is constantly changing, this change of direction from age to age is unavoidable. He did not attempt to estimate precisely the rate of motion, but, "in a general way," he considered that it "cannot certainly be less than that which the earth has in her annual orbit." At the same time he expected that future astronomers would assist him in determining the direction of the solar motion; and he added that he had "begun a series of observations upon several zones of double stars," with the view of establishing or overturning his hypothesis. His estimate of the rate of the sun's motion may not be correct. Probably it is only from five to nine miles a second, or less than half what he made it: but science has accepted his view of the point, to which the solar system has, for an hundred years, been advancing. Recently α Lyræ (Vega) has been claimed as the point we are now making for.

In the years that followed his first papers on The