Although the microscope is more capable of affording amusement than most philosophical instruments, there are few who have used it for any length of time but have discovered that it is an important aid in scientific research. Even those who have purchased their first instrument to wile away a leisure hour have gradually got interested in its structure, and the nature of the objects investigated, so that, although beginning in play, they have ended in work. No one can know that they have observed, for the first time, a fact new in the history of science, without the rising of the feeling that constitutes the discoverer in science—the seeker after truth. It is thus that many great microscopic observers have arisen among classes who have had no previous scientific education that has prepared the world for the result of their labours. The structure of the instrument, involving as it does the greatest mechanical accuracy with the most interesting problems of optical science, has excited the attention of one set of inquirers, whose labours have resulted in the present perfection of the instrument. On the other hand, the habits of minute observation developed by the daily use of the microscope have produced a number of observers, whose contributions to science are known wherever its progress is regarded with interest. To those who are pursuing the latter path, all works on those departments of science to which the microscope is applied are of interest.