. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. THE MICROSCOPE. 41 Instruments to perfection, and during the manufacture of the object-glasses, he effected a most important improvement in their construction, which he thus describes:*—"Having applied Mr. Lister's principles with a degree of success never anticipated, so perfect were the corrections given to the achromatic object-glass, so completely were the errors of sphericity and dispersion balanced or dest
. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. THE MICROSCOPE. 41 Instruments to perfection, and during the manufacture of the object-glasses, he effected a most important improvement in their construction, which he thus describes:*—"Having applied Mr. Lister's principles with a degree of success never anticipated, so perfect were the corrections given to the achromatic object-glass, so completely were the errors of sphericity and dispersion balanced or destroyed, that the cir- cumstance of covering the object with a plate of the thinnest glass or talc disturbed the corrections, if they had been adapted to an uncovered object, and rendered an object-glass which was perfect under one condition sensibly defective under the ; This defect, if that be called a defect which arose out of an improvement, he (Mr. Ross) first detected, and immediately suggested the means of correcting, and in 1837 communicated his discovery to the Society of Arts, in a paper published in the fifty-first volume of their Transactions, to which paper the author would refer those of his readers who would wish to enter more fully into the subject; the desired object being effected by separating the anterior lens in the combination from the other two; and figure 22, which is a section of an achromatic object- glass, will explain how the principles established by Mr. Ross were put into practice. A represents a tube, in the end of which the anterior lens is set; this shdes on the cylinder, B, containing the remainder of the combination; the tube, A, holding the lens nearest the object, may then be moved upon the cylinder, B, for the purpose of varying the distance, according to the thickness of the glass covering the object, by turning the » Op. at. p. Fig. Please note that these images are extracted from scanned page images that may have bee
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