tating in one direction, as in the ordinary radiometer, is suspended by a glass fibre, which it twists in opposite directions alternately. The movement is started by rotating the whole apparatus through a small angle, and the observation consists in noting the successive amplitudes of vibration when the instrument is left to itself, a mirror and spot of light being employed for this purpose. The results of these experiments leave no reasonable doubt that the repulsion is due to the internal movement of the molecules of the residual gas.
In 1875 Mr. Crookes received the award of a Royal medal from the Royal Society for his various chemical and physical researches; and in 1876 he was elected a Vice-President of the Chemical Society.
Previous to his researches on "Repulsion," Mr. Crookes began to investigate so-called spiritualism. As far as it extended, his inquiry into the subject convinced him that certain phenomena obtained under test conditions in his own house were due neither to tricks, mechanical arrangements, nor to legerdemain. He inclined to the opinion that the "medium" possessed what Mr. Sergeant Cox calls psychic force, but he had arrived at no definite conclusions as to the cause of the phenomena when he decided to discontinue their investigation.
Mr. Crookes is the author of "Select Methods in Chemical Analysis," of "The Manufacture of Beet-Root Sugar in England," and of a "Handbook of Dyeing and Calico Printing." He is also joint author of the English adaptation of Kerl's "Treatise on Metallurgy." He has edited and enlarged the last two editions of Mitchell's "Manual of Practical Assaying," and translated into English and edited Reimann's "Aniline and its Derivatives," Wagner's "Chemical Technology," and Auerbach's "Anthracen and its Derivatives."
It is claimed that Mr. Crookes was the first to apply photography to the investigation of the solar spectrum, but his earlier researches were so numerous that it is impossible to refer to them all. We may, however, mention his papers "On the Opacity of the Yellow-Soda Flame to Light of its own Color," "On the Measurement of the Luminous Intensity of Light," "On a New Binocular Spectrum Microscope," and "On the Optical Phenomena of Opals."
