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594 accompanied it, and continued to teach in a manner that secured the approbation of the directors. In 1818 his sphere of educational duty was extended, in consequence of a resolution of the directors of the college, that a half-yearly course of lectures on practical astronomy should be given to the students, and that Mr. Wallace should be the lecturer. As this course also was to be combined with instructions on the manner of making celestial observations, a small observatory was erected for the purpose, and furnished with the necessary instruments. This addition to the routine of a military education, has done much to remove the objections often brought against our bravest officers of the army, on account of their deficiency in the science of their profession.

Another movement was now to occur in the changeful career of Mr. Wallace. In 1819 Professor Play fair died; Mr. (afterwards Sir John) Leslie was appointed to succeed him; and by this transference the chair of mathematics in the university of Edinburgh became vacant, and open to competition. The height of Wallace's ambition was to obtain a Scottish professorship, and accordingly he threw himself into the contest with his whole heart and energy. In the trial of candidates, which was a keen one, he was successful, an.d he brought the maturity of his experience as a teacher, as well as his rich scientific acquirements as a mathematician, to a chair but too often filled with men unpractised in the common ways of life, and whose whole occupation is to muse and dream over a problem. Many of the scientific men of the present day can still remember, with gratitude, the efficiency with which Mr. Wallace discharged the duties of his professorship, and the impulse which his teaching imparted to their studies. He thus continued to labour till 1838, when he was obliged to retire from office in consequence of ill health; and on his retirement, government expressed its sense of the value of his services, both at Sandhurst and Edinburgh, by conferring on him a pension; and the university of Edinburgh, by making him a doctor of laws. Five years of private life succeeded, during which, however, his mind was not idle in his favourite pursuits, as was attested by his productions during this period, while he was unfitted by sickness for the usual intercourse of society. Having reached the age of seventy, five, he died at Edinburgh, on the 28th of April, 1843.

Besides those scientific articles which we have already mentioned, Professor Wallace, in the earlier part of his life, was a contributor to Leybourne's "Mathematical Repository," and the "Gentleman's Mathematical Companion:" he was also author of the principal mathematical articles in the "Edinburgh Encyclopædia," and the fourth edition of the "Encyclopædia Britannica." To these productions the following may be added:—

In 1808, he presented to the Royal Society of Edinburgh an article entitled "New Series for the Quadrature of the Conic Sections, and the Computation of Logarithms."

In 1823, he presented another, entitled, "Investigation of Formulae for finding the Logarithms of Trigonometrical Quantities from one another."

In 1831, he presented another, entitled, "Account of the Invention of the Pantograph, and a Description of the Eidograph." Of this instrument, called the eidograph—from ειδος, a form, and γραφειν, to draw—he was himself the inventor; and, like the pantograph, it is used for the purpose of copying plans or other drawings, on the same or on different scales. Professor Wallace was also the inventor of the chorograph, an instrument for describing on paper any triangle