. Darwin and modern science; essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of the Origin of species. Darwin, Charles, 1809-1882; Science; Evolution. The light-curve of a variable star 557 3 and 4, and then again perhaps it may return to between 2 and 3, and so forth. With practice he learns to evaluate the brightness down to small fractions of a magnitude, even a hundredth part of a magnitude is not quite negligible. For example, in observing the star RR Centauri five stars were in general used for comparison by Dr Ro
. Darwin and modern science; essays in commemoration of the centenary of the birth of Charles Darwin and of the fiftieth anniversary of the publication of the Origin of species. Darwin, Charles, 1809-1882; Science; Evolution. The light-curve of a variable star 557 3 and 4, and then again perhaps it may return to between 2 and 3, and so forth. With practice he learns to evaluate the brightness down to small fractions of a magnitude, even a hundredth part of a magnitude is not quite negligible. For example, in observing the star RR Centauri five stars were in general used for comparison by Dr Roberts, and in course of three months he secured thereby 300 complete observations. When the period of the cycle had been ascertained exactly, these 300 values were reduced to mean values which appertained to certain mean places in the cycle, and a mean light-curve was obtained in this way. Examples of light curves will be found in Figs. 5 and 7 below. Jan. 1, 1900 Scale of hours Mag 12 13 14 15 16. Fig. 5. Light curve of ER Centauri. I shall now follow out the results of the observation of RR Centauri not only because it affords the easiest way of explaining these investigations, but also because it is one of the stars which furnishes the most striking results in connection with the object of this essay \ This star has a mean magnitude of about 7\, and it is therefore invisible to the naked eye. Its period of variability is 14^ 32^ 108-76, the last refinement of precision being of course only attained in the final stages of reduction. Twenty-nine mean values of the magnitude were determined, and they were nearly equally spaced over the whole cycle of changes. The black dots in Fig. 5 exhibit the mean values determined by Dr Roberts. The last three dots on the extreme right are merely the same as the first three on the extreme left, and are repeated to show how the next cycle would begin. The 1 See Monthly Notices Vol. 63, 1903, p. Please note that these images are
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