Page:Popular Science Monthly Volume 10.djvu/759

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7,549,101. Add these digits, 7+5+4+9+1+0+1=27, and 2+7=9.

But we have extended already this article to a greater length than we intended, simply wishing to give the origin and history of the decimal notation as far as it can be traced, and will close by stating that this notation is every way adapted to the practical operations of business, as well as the most abstruse mathematical investigations. In whatever light it is viewed, the decimal notation must be regarded as one of the most striking monuments of human ingenuity, and its beneficial influence on the progress of science and the arts, on commerce and civilization, must win for its unknown author the everlasting admiration and gratitude of mankind.



AMONG the active and successful scientific workers of England, at the present time, the gentleman whose portrait we give this month is one of the foremost. Though only in the meridian of his manhood, he has made two discoveries—those of the metal thallium and of the radiometer which will immortalize his name; while his minor labors in the field of science, both in the laboratory and in the editorial office, are in an unusual degree important and valuable.

William Crookes was born in London, in 1832. His scientific career commenced in 1848, when he entered the Royal College of Chemistry as a pupil of the distinguished chemist Dr. Hoffmann, now of the University of Berlin. He had gained the Ashburton scholarship at the age of seventeen. After two years of study, Dr. Hoffmann appointed him, first, his junior, and then his senior assistant, which post he held until 1854, when he went to Oxford to superintend the meteorological department of the Radcliffe Observatory. In 1855 he was appointed Teacher of Chemistry at the Science College, Chester. In 1859 he founded the Chemical News, and in 1864 he became editor of the Quarterly Journal of Science.

Mr. Crookes's researches were begun while at the Royal College of Chemistry, his first paper, "On the Seleno-Cyanides," being published in the Quarterly Journal of the Chemical Society, in 1851. Since then he has been almost uninterruptedly engaged in private research on subjects connected with chemistry and physics.

In 1861 Mr. Crookes discovered, by means of spectral observations and chemical reactions, the metal thallium; and in June, 1862, and February, 1873, he laid before the Royal Society an account of