10,000,000,000, the light of Sirius. 91,000,000,000, the light of a star of magnitude 1. 9,100,000,000,000, the light of one of magnitude 6. The square roots of these numbers show the number of times we should increase the actual distance of the sun in order that it might shine as a star of the corresponding magnitude. These numbers and the corresponding parallax are as follows: Sirius; Distance = 100,000: Parallax = 2″.06 Mag. 1 ” 302,000: ” 0″.68 ” 2 ” 479,000: ” 0″.43 ” 3 ” 759,000: ” 0″.27 ” 4 ” 1,202,000: ” 0″.17 ” 5 ” 1,906,000: ” 0″.11 ” 6 ” 3,020,000: ” 0″.07 These parallaxes are those that the sun would have if placed at such a distance as to shine with the brightness indicated in the first column. They are generally larger than those of stars of the corresponding magnitudes, from which we conclude that the sun is smaller than the brighter of the stars. PREVENTIVE INOCULATION. (II.) BY DR. W. M. HAFFKINE, DIRECTOR-IN-CHIEF, GOVERNMENT PLAGUE RESEARCH LABORATORY, BOMBAY. In a previous paper I reviewed briefly the history of preventive inoculation and described the results of my attempts to secure a ‘virus fixé’ in the case of cholera. It will be remembered that the two vaccines finally obtained protected guinea pigs successfully against all possible forms of cholera infection. It was now necessary to ascertain whether the same protection could be given to man which was observed in animals. For this purpose it was essential to first of all prove the perfect harmlessness of the operation. This was established by very careful observations of medical men and scientists who were inoculated in Europe soon after the results of the above investigations were published. The inoculation causes a rise of temperature and general discomfort, which lasts one or two days, and some pain at the seat of the injection, which disappears in a few days. The fever and discomfort induced are, on the whole, shorter in duration, though often more intense, than those caused by vaccination against smallpox. The effect disappears within a few days and the individual returns to his usual condition of health.