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CROOKES.

thallium. His first paper on this subject was read before the Boyal Society Dec. 11, 1873, and between that time and 1880 Mr. Orookes sent to the Society eight other communications on collateral sub- jects, which are all published in the "Philosophical Transactions." One important result of these in- vestigations is the Radiometer. In 1875 Mr. Crookes received from the Koyal Society the award of a Boyal Medal for chemical and physical researches. In 1876 he was elected a Vice-President of the Chemical Society, and the next year a mem- ber of the Council of the Royal Society. In 1877 he described the Otheoscope, — a greatly modified Radiometer, susceptible of an al- most endless variety of forms. In 1878 he gave before the Royal Society a " Bakerian Lecture," con- taxuing another long series of ex- periments and observations on " Re- pulsion resulting from Radiation." In 1879 the Royal Society published in its ** Philosophical Trtmsactions " records of Mr. Crookes's experi- ments on "Molecular Physics in High Vacua." In the same year appeared a further paper on "Repulsion resulting from Ra- diation ; " and he was again ap- pointed Bakerian Lecturer to the Royal Society, his subject the " Il- lumination of Lines of Molecular Pressure, and the Trajectory of Molecules." In 1879, in the form of a lecture delivered before the British Association for the Advance- ment of Science, under the title of "Radiant Matter," he compressed his researches on the electric dis- charge in high vacua. In this lec- ture, fully illustrated by experi- ments, he showed that gases when very highly rarified lose most of the ordmary properties of matter, and pass into a fourth or ultra- gaseous condition. In 1880 the French Academic des Sciences be- stowed on Mr. Crookes an extra- ordinary prize of 3000 francs and a Gold Medal, in recognition of his

discoveries in Molectdar Physics and Radiant Matter. In 1881 Mr. Crookes acted as a Juror at the In- ternational Exhibition of Elec- tricity in Paris. In this official position he was not entitled to a medal, but in the official report, his fellow jurors, after discussing the merits of four systems of incandes- cent lamps, declared — "None of them would have succeeded had it not been for these extreme vacua which Mr. Crookes has taught us to manage." It is stated 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. Mr. Crookes is the author of " Se- lect Methods in Chemical Analysis," — a second edition (1883) is in course of preparation ; of the "Manufacture of Beet-root Sugar in England ;" of a " Handbook of Dyeing and Calico-Printing ;" and of a Manual of "Dyeing and Tissue-Printing" (1882),— one of the " Technological Handbooks prepared for the examinations of the City and Guilds of London In- stitute. He is also joint author of the English adaptation of Kerl's "Treatise on Metallurgy." He has edited the last three editions of Mitchell's " Manual of Practical Assaying," and has translated into English and edited Reimann's "Aniline and its Derivatives," Wagner's " Chemical Technology," Auerbach's "Anthracen and its Derivatives," and Ville's "Artifi- cial Manures," a second edition of which appeared in 1882. Mr. Crookes is an authority on sanitary questions, especially the disposal of town-sewage, and his views have been laid before the public in two pamphlets, "A Solution of the Sewage Question " and " The Pro- fitable Disposal of Sewage." In conjunction with Drs. Odling and Tidy, Mr. Crookes is now investi- gating the sanitary condition of the water-supply of London.