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While engaged in these avocations, as well as in professional practice, 

 which about the year 1813 began to be considerable, Dr. Roget was not 

 unmindful of his early passion for the exact sciences. Of Mathematics 

 and Natural Philosophy he made a practical study ; and in the year 1814 

 he contrived a sliding-rule so graduated as to be a measure of the powers 

 of numbers, in the same manner as the scale of Gunter, then in common 

 use, was a measure of their ratios. It is a logo-logarithmic rule, the 

 slide of which is the common logarithmic scale, while the fixed line is 

 graduated upon the logarithms of logarithms. The consequence is that 

 powers are read as easily as products are on the common rule, and the 

 arrangement is such that high powers of quantities little exceeding unity, 

 so much wanted in compound interest, statistics, &c, are read off on 

 a single setting. His paper thereon, which also describes other ingenious 

 forms of the instrument, was communicated by Dr. Wollaston to the 

 Royal Society, and read on the 17th of November, 1814. It appears in 

 the Philosophical Transactions for 1815, p. 9. It was through this 

 communication that he gained admission to the Society. He was elected 

 Fellow on the 16th of March, and admitted on the Oth of April, 1815. 

 The date of this epoch in his life is noteworthy in relation to the im- 

 portance which he attached to his deliverance in 1803 from the clutches 

 of Bonaparte. The year in which his paper was read was that of his young 

 friend Edgeworth's release. The manner in which the interval had been 

 employed affords a measure of the loss which he and others would have 

 incurred had he been destined to the like exile. 



The next decade in Dr. Roget's life was a period of active industry, passed 

 in the society of many of the most distinguished men of his time. Besides 

 his occupations above specified, he employed his pen in the production of 

 various published writings. In 1815 he contributed a paper to the Medico- 

 Chirurgical Transactions, vol. vii. p. 290, "On a Change in the Colour of 

 the Skin produced by the internal use of Nitrate of Silver." At various 

 periods between 1815 and 1822 he wrote the following treatises and articles 

 in the Supplement to the sixth edition of the 1 Encyclopaedia Britannica;' 

 viz. Ant, Apiary, Barthez, Beddoes, Bee, Btchat, Brocklesby, 

 Broussonet, Camper, Cranioscopy, Currie, Deaf and Dumb, Ka- 

 leidoscope, and Physiology. In 1818 he wrote a letter " On the Kalei- 

 doscope" to the Editors of the 1 Annals of Philosophy,' w hich was published 

 in vol. xi. p. 375. That year was saddened by the melancholy death of his 

 uncle, Sir Samuel Romilly. In July 1820 he was appointed Physician to the 

 Spanish Embassy, which office he retained for many years. In the same year 

 he wrote a letter to Mr. Travers on a voluntary action of the Iris, which was 

 published by Mr. Travers in his work * On the Diseases of the Eye;' and 

 an Appendix to Larkin's 1 Introduction to Solid Geometry and to the Study 

 of Crystallography,' in which Dr. Roget demonstrates the ratios subsisting 

 between the volumes of solids composing the artificial series, together with 

 the various inclinations of their faces. In 1821 he wrote "Observations on 



