Societies and Academies

Abstract

LONDON

Royal Astronomical Society, December 14, 1877.—Dr. Huggins, F.R.S., in the chair.—A paper by Dr. Wolf, of Zurich, set forth that the sun-spot period varies from seven to sixteen years, eleven years being the average.—A paper by Mr. C. V. Boys described a new astronomical clock. Mr. Christie and Lord Lindsay criticised it.—A photograph of the sun was presented by M. Janssen. It is one of those taken daily at Meudon, measuring one foot in diameter. Dr. De la Rue said it was the finest example of celestial photography he had ever seen. It was not taken with an equatorial, but an instrument after the fashion of the Kew photoheliograph with a 51/2-inch object-glass. The picture was not taken at the principal focus, but in that of a secondary magnifier, corrected independently of visual focus. He pointed out the tornadoes visible on the photograph, and spoke of the importance of a physical observatory to register the changes which occur on a tremendous scale every hour, sum-spots being phenomena of comparatively small importance. Capt. Abney spoke in corroboration, and said that M. Janssen at first thought these photographed tornadoes had an atmospheric origin. Mr. Christie said that similar phenomena had been found on the Greenwich photographs, and they had nothing to do with the collodion.—Mr. Glaisher read a paper on the law of force tending to any point whatever in the plane of motion in order that the orbit may always be a conic.—Mr. Lynn gave a description of Mr. Howlett's drawing of the solar spot of October 31 to November 3, being about 15″ diameter.—Lord Lindsay concluded the description of his spectroscope for nebulæ referred to last month.—Mr. Christie made some remarks and criticised it, and the meeting then adjourned.