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  till he has completed the twenty-first year of his age, and actually served with his regiment, as a commissioned officer, three years abroad, or four years at home. Applications for admission must be made to the governor, through the commanding-officer of the regiment to which the candidate belongs, and the governor transmits the application to the commander-in-chief for his Majesty’s approbation. Such examination as may be deemed requisite, is required previous to admission. Each student of this department pays into the funds of the college thirty guineas annually, and after a certain period he is obliged to keep a horse, for the purpose of receiving such instruction as is given in the field. There are public examinations half-yearly, conducted on the same principle as the half-yearly examinations of the Junior Department. Such officers as have gone through the regular course of studies, and have passed this examination with credit, receive certificates that they are duly qualified for staff-appointments, signed by the board who examined them, and sealed with the seal of the college.

Officers or students of the first department, non-commissioned officers, and other military persons belonging to the college, as well as the gentlemen cadets of the junior department, are subject to the articles of war, for which purpose, the latter are placed on the establishment of the army, and receive 2s. 6d. per day. This money contributes towards the expence of their education. The gentlemen cadets wear military uniforms.

The general staff of the college consists of the governor, the lieutenant-governor, the inspector-general of instruction, and the chaplain, who, besides performing divine service, teaches the evidences and principles of Christianity. The rest of the staff are exclusively occupied with the finances of the college.

In 1801, five hundred acres of land were purchased at Sandhurst near Bagshot; and on this space large and commodious buildings have been erected, into which the Junior Department has been recently removed from Great Marlow; the Senior Department remaining at Farnham, which is no great distance from Sandhurst.

The reader will find an account of some establishiments for the education of those destined for the service of the East India Company, under the word, in this Supplement.(.)  ACHROMATIC GLASSES. The theory and construction of achromatic glasses have been already treated at some length, and with considerable ability, under the article Telescope, in the Encyclopædia. A subject of such importance, however, seems to require a distinct and prominent place. We purpose, therefore, to review the whole again; and while we separate the exposition of principles from the complicated calculations that depend on them, we shall endeavour to spread more interest over the discussion, by tracing the successive steps in the progress of optical discovery.

The invention of the telescope, by which the powers of vision are extended to the utmost boundaries of space, forms an epoch in the history of science. The human intellect had at last emerged from the long night of error, and begun to shine with unclouded lustre. The age of erudition, which arose on the revival of letters, had been succeeded by the age of science and philosophy. The study of the ancient classics had infused some portion of taste and vigour: But men did not long remain passive admirers; they began to feel their native strength, and hastened to exert it. A new impulsion was given to the whole frame of society; the bolder spirits, bursting from the trammels of authority, ventured to question inveterate opinions, and to explore, with a fearless yet discerning eye, the wide fields of human knowledge. Copernicus had partly restored the true system of the world; Stevinus had extended the principles of mechanics; the fine genius of Galileo had detected and applied the laws of motion; the bold excursive imagination of Kepler had, by the aid of immense labour, nearly completed his discovery of the great laws which control the revolutions of the heavenly bodies; and our countryman, Napier, had just rendered himself immortal by the sublime discovery of logarithms. At this eventful period, amidst the fermentation of talents, the refracting telescope was produced by an obscure glass-grinder in Holland,—a country then fresh from the struggle against foreign oppression, and become the busy seat of commerce and of the useful arts. Yet the very name of that meritorious person, and the details connected with his invention, are involved in much obscurity. On a question of such peculiar interest, we shall afterwards endeavour to throw some light, by comparing together such incidental notices as have been transmitted by contemporary writers. In the meantime, we may rest assured, that the construction of the telescope was not, as certain authors would insinuate, the mere offspring of chance, but was, like other scientific discoveries, the fruit of close and patient observation of facts, directed with skill, and incited by an ardent curiosity. A new, and perhaps incidental appearance, which would pass unheeded by the ordinary spectator, arrests the glance of genius, and sets all the powers of fancy to work. But the inventor of the telescope, we are informed, was acquainted besides with the elements of geometry, which enabled him to prosecute his views, and to combine the results with unerring success. No sooner was this fine discovery—admirable for the very simplicity of its principle—whispered abroad, than it fixed the attention of the chief mathematicians over Europe. Kepler, with his usual fertility of mind, produced a treatise on Dioptrics, in which he investigated at large the distinct effects of the combinations of different lenses. Galileo, from some very obscure hints, not only divined the composition of the telescope, but actually constructed one, with a concave eye-glass, which still bears his name. This telescope is shorter, but gives less light than another one proposed by Kepler, and called the astronomical telescope, which inverts the objects, and consists likewise of only two lenses, that next the eye being convex. With such an imperfect instrument—the same, indeed, though of rather higher magnifying power, with our modern opera-glass—did the Tuscan artist, as our great poet quaintly styles the philosopher, venture to explore 