Page:Hector Macpherson - Herschel (1919).djvu/25

Rh April, 1777, he commenced to make sketches in pen and ink of the markings on the surface of Mars, and in the following year of those on Jupiter. His attention was not confined to the members of the Solar System, and in 1777 he commenced a series of observations on the variable star, Omicron—or Mira—Ceti. As early as 1778 he had conceived the idea of attempting to determine by measures of close doubles the annual parallax or apparent displacement of a star in the sky due to the earth's change of position as it moves in its orbit. From this parallax, the distance of a star is determined. Before Herschel's time, astronomers had made many attempts to measure stellar parallax, but owing to the great distance of even the nearest stars and the consequent smallness of the displacement, and also because of the comparative imperfection of astronomical instruments, all these efforts had failed. Herschel was particularly interested in the problem, and made several attempts to solve it, but was unsuccessful. It was not until 1838 that the first determinations of stellar parallax were made. Herschel's attempts were not altogether in vain, however, for while tackling the problem, he was led to the study of double stars, which resulted, after many years, in one of his greatest discoveries. At the same time he executed his first review of the heavens with his 7-foot Newtonian reflector. The review only extended to the first four magnitudes: it was in itself a mere beginning, but it was the starting-point of his work on stellar distribution.

Herschel soon became known to the cultured public of Bath, not only as a prominent musician, but also as an amateur astronomer of considerable eminence. His introduction to literary and scientific circles in the town was a somewhat unconventional one. In his diary, under the date December, 1779, there occurs the following entry: "About the latter end of this month, I happened to be engaged on a series of observations on