. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 172 PRACTICAL TEEATISE ON THE MICROSCOPE. the definition produced by an achromatic compound micro- scope will depend upon the accuracy with which the aberra- tions, both chromatic and spherical, are balanced, together with the general perfection of the workmanship. Now, in WoUaston's doublets and Holland's triplets, there are no means of producing a balance of the aberrations, as they are composed of convex lenses on
. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 172 PRACTICAL TEEATISE ON THE MICROSCOPE. the definition produced by an achromatic compound micro- scope will depend upon the accuracy with which the aberra- tions, both chromatic and spherical, are balanced, together with the general perfection of the workmanship. Now, in WoUaston's doublets and Holland's triplets, there are no means of producing a balance of the aberrations, as they are composed of convex lenses only; therefore the best that can be done, is to make the aberrations a minimum; the remaining positive aberration in these forms, produces its peculiar effect upon objects (particularly the detail of the thin transparent class) which may lead to misapprehension of their true structure; but with the achromatic object-glass, where the aberrations are correctly balanced, the most minute parts of an object are accurately displayed, so that a satisfactory judgment of their character may be formed. It will be seen by fig. 119, that when a certain angular pencil, A O A, pro- ceeds from the object, O, and is incident on the plane side of the first lens, if the combination be removed from the object, as in fig. 120, the extreme rays of the pencil impinge on the. Fig. 119. rig. 120. more marginal parts of the glass, and as the refractions are greater here, the aberrations will be greater also. Now, if two compound object-glasses have their aberrations balanced, one being situated as in fig. 119, and the other as in fig. 120, and the same disturbing power applied to both, that in which the angles of incidence and the aberrations are smaU, will not. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Quekett, John, 1815-1861
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