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much that might otherwise appear strange. The Author has thought it particularly needful to restrain himself, in treating of certain very important subjects which are fully discussed in treatises expressly devoted to them (such, for example, as the structure of Insects, and the Primary Tissues of Vertebrata), in order that he might give more space to those on which no such sources of information are readily accessible. For the same reason he has omitted all reference to the applications of the Microscope to Pathological inquiry; a subject which would interest only one division of his readers, and on which it would have been impossible for him to compress, within a sufficiently narrow compass, a really useful summary of what such readers can readily learn elsewhere. So again, the application of the Microscope to the detection of Adulterations in Food, &c., is a topic of such a purely special character, and must be so entirely based on detailed descriptions of the substances in question, that he has thought it better to leave this also untouched.
It has been the Author's object throughout, to guide the possessor of a Microscope to the intelligent study of any department of Natural History, that his individual tastes may lead him to follow out, and his particular circumstances may give him facilities for pursuing. And he has particularly aimed to show, under each head, how small is the amount of reliable knowledge already acquired, compared with that which remains to be attained by the zealous and persevering student. Being satisfied that there is a large quantity of valuable Microscope-power at present running to waste in this country,-being applied in such desultory observations as are of no service whatever to science, and of very little to the mind of the observer, he will consider the labor he has bestowed upon the production of this Manual as well repaid, if it should tend to direct this power to more systematic labors, in those fertile fields which only await the cultivator to bear abundant fruit.
In all that concerns the working of the Microscope, the Author has mainly drawn upon his own experience, which dates back almost to the time when Achromatic Object-glasses were first constructed in this country. He would be ungrateful, however, if he were not to acknowledge that he has derived many valuable hints from the Practical Treatises of Mr. Quekett and Dr. Beale, and from the Micrographic Dictionary of Messrs. Griffith and Henfrey. And among the works by which he has been
specially aided in treating of the Applications of the instrument, he would especially name Mr. Quekett's valuable Lectures on Histology (Vegetable and Animal), Mr. Ralfs's beautiful Monograph on the British Desmidieæ, Prof. W. Smith's on the Diatomaceae (which will, when complete, be quite worthy to take rank with the preceding), and the Micrographic Dictionary.
All the Illustrations have been drawn by Mr. W. Bagg, and have been engraved under his superintendence; and the Author ventures to affirm, that for fidelity as well as for beauty of execution, they will bear comparison with any Microscopic delineations yet executed on wood. A large proportion of the subjects are original; the sources of all that are not so, are specified in the list (p. xvii).
The Author feels that some apology is due for the long delay which has attended the appearance of this work. When it was first announced as forthcoming, his full intention was to apply himself immediately to its production; but the unexpected demand for new editions of his two large Treatises on Physiology, required that the whole of his disposable time and attention should be given up during two years to carrying these through the press. When he at last found himself free to apply himself to the "Microscope," he fully expected that the forward state of his preparations would enable him to complete it by October, 1855. But in this expectation he has been disappointed by the occurrence of two severe attacks of indisposition, which compelled him for a time to suspend all mental exertion, and have rendered it necessary for him carefully to abstain from overtasking himself; so that he feels assured that those who have kindly waited for the appearance of this volume, will not, when acquainted with these circumstances, blame him for a delay, the causes of which have lain so completely beyond his control.
UNIVERSITY HALL, LONDON,
Feb. 9, 1856.