into a single real motion of the Solar System, as far as that will answer the known facts, and only to attribute to the proper motion of each particular star the deviations from the general law the stars seem to follow in those movements."
Herschel treated the problem in the simplest manner. Dealing with the proper motions of seven bright stars—Sirius, Castor, Procyon, Pollux, Regulus, Arcturus, and Altair—he separated their real from their apparent motions by simple geometrical methods, and reached the conclusion that the Solar System was moving towards a point in the constellation Hercules, the "apex" of the solar motion being marked by the star Lambda Herculis. "We may," he said, "in a general way estimate that the solar motion can certainly not be less than that which the Earth has in her annual orbit." In 1805, Herschel again attacked the problem, making use of Maskelyne's table of the proper motions of thirty-six stars. His result was in the main confirmatory of his earlier conclusions, the "apex" being again located in the constellation Hercules.
Herschel's brilliant discovery was regarded with considerable incredulity by several of his contemporaries and successors. They seemed to feel that the data on which he worked were too slender for a trustworthy result to be deduced. Bessel, the greatest practical astronomer of the next generation, maintained that there was no evidence in favour of a motion towards a point in Hercules; and even Sir John Herschel rejected his father's conclusions. In 1837, Argelander attacked the question from a study of the motion of 390 stars. The result of his investigation was to confirm abundantly Herschel's conclusions. Since Argelander's time, determination after determination has been made, by many illustrious mathematicians of each generation. Every refinement has been exhausted, "only," in the striking words of Ball, "to confirm the truth of that
