PEEFACE TO THE SEVENTH EDITION xi 



desirable that even this end should be sought intelligently. The social 

 influence of the Microscope as an instrument employed for recreation 

 and pleasure will be greater in proportion as a knowledge of the 

 general principles on which the instrument is constructed are known, 

 and as the principles of visual interpretation are understood. The 

 interests of these have been specially considered in the following- 

 pages ; but such an employment of the Microscope, if intelligently 

 pursued, often leads to more or less of steady endeavour on the part 

 of amateurs to understand the instrument and use it to a purpose 

 in some special work, however modest. This is the reason of the 

 great increase of ' Clubs ' and Societies of various kinds, not only in 

 London and in the provinces, but throughout America; and these 

 are doing most valuable work. Their value consists not merely in the 

 constant accumulation of new details concerning minute vegetable 

 and animal life, and the minute details of larger forms, but in the 

 constant improvement of the quality of the entire Microscope on its 

 optical and mechanical sides. It is largely to Amateur Microscopy 

 that the desire and motive for the great improvements in object-glasses 

 and eye-pieces for the last twenty years are due. The men who have 

 compared the qualities of respective lenses, and have had specific ideas 

 as to how these could become possessed of still higher qualities, have 

 been comparatively rarely those who have employed the Microscope 

 for professional and educational purposes. They have the rather 

 simply used employed in the execution of their professional work 

 the best with which the practical optician could supply them. 

 It has been by amateur microscopists that the opticians have been 

 incited to the production of new and improved objectives. But it 

 is the men who work in our biological and medical schools that 

 ultimately reap the immense advantage not only of greatly im- 

 proved, but in the end of greatly cheapened, object-glasses. It is 

 on this account to the advantage of all that the amateur micro- 

 scopist should have within his reach a handbook dealing with the 

 principles of his instrument and his subject. 



To the medical student, and even to the histologist and patho- 

 logist, a treatise which deals specifically with the Microscope, its 

 principles, and their application in practice, cannot fail, one may 

 venture to hope, to be of service. 



This book is a practical attempt the result of large experience 

 and study to meet this want in its latest form ; and I sincerely 

 desire that it may prove useful to many. 



W. H. DALLINGER. 



LONDON : 1891. 



