THE SCIENTIFIC LABORS OF WILLIAM CROOKES. 74 1 



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 ampli- 

 tudes 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 So- 

 ciety. 



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 in- 

 vestigation. 



Mr. Crookes is the author of " Select Methods in Chemical Analy- 

 sis," 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 Rei- 

 mann's " Aniline and its Derivatives," Wagner's " Chemical Tech- 

 nology," 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 Mi- 

 croscope," and " On the Optical Phenomena of Opals." 



