GLASGOW SOCIETY OF FIELD NATUKALISTS. 119 



imperfect instruments that Leuwenhoek, Swammerdam, and others, 

 examined the minute forms of nature, and afterwards described 

 them so correctly that we cannot help wondering how it was pos- 

 sible for them to do so. Robert Eoohe published in 1667 his 

 Micrographia, a wonderful production for those times, which was, 

 however, soon eclipsed by the researches of Leuwenhoek, which 

 were first published in the transactions of the Philosophical Society 

 in 1673, as well as by those of Greio and Malpighi, the former of 

 whom laid the foundation for our knowledge of the vegetable 

 tissues, and the latter of the tissues of the animal body. Small 

 glass globules, by the application of which to the simple microscope, 

 instead of convex lenses, an enormous magnification was obtained, 

 were first used by Dr. Hooke and Hartsoeker. Stephen Gray dis- 

 covered in 1696 that drops of water, containing animalcules, if 

 hung to the end of a wire and held close to the eye, showed these 

 animalcules enormously magnified. Whilst many observers of 

 those times added discovery to discovery, little improvement was 

 efiected in the simple microscope until the celebrated Dr. Nathaniel 

 Lieherkuhn of Berlin, about the year 1740, brought out his im- 

 proved instrument, which consists of a short tube of about 1 inch 

 diameter, in one end of which is a bi-convex lens for collecting the 

 rays and throwing them on a concave silver speculum near to the 

 other end, the latter having a round aperture in the centre. The 

 rays are reflected by this siDeculum to its focus, about one-half inch 

 distance, in which is placed the opaque object glued to a little disc 

 adjustable by a wire in the side of the instrument. The object 

 brilliantly lit up is viewed by a small lens of half-inch focus through 

 the circular opening of the speculum. This instrument, which 

 was only adapted for viewing opaque objects, was held by a handle. 

 Leuwenhoek's microscopes were nearly all single lenses fitted in a 

 tube having a slide holder. He had hundreds of such microscopes, 

 one each for one or two objects. 



The first three compound microscopes worthy of notice are 

 those of Dr. Hooke, Eustachio Divini, and Philip Bonnani. Dr. 

 Hooke describes his instrument in the Micrographia, in 1667, as 

 being 3 inches diameter, 7 inches long, and having four draws. 

 It had three glasses, a small object-glass, a middle glass, and a 

 deep eye-piece. Divini's microscope was described, in 1668, as 

 having an object-glass, a middle glass, and two eye-glasses, which 

 were plano-convex, touching each other in the centre of their 



