126 THE HISTORY AND DEVELOPMENT OF THE MICROSCOPE 



that after the year 1000, minds having reopened to hope and in- 

 tellects to study, there began to dawn some light of science, so that 

 in 1276 a Franciscan monk, Roger Bacon, of Ilchester, in his ' Opus 

 Majus,' dedicated and presented by him to Clement IV., could show 

 many marvellous things, and amongst these the efficacy of crystal 

 lenses, in order to show things larger, and in this wise he says make 

 of them ' an instrument useful to old men and those whose sight is 

 weakened, who in such a way will be able to see the letters suf- 

 ficiently enlarged, however small they are.' As long as no documents 

 anterior to him are discovered, Roger Bacon may be considered the 

 first inventor of convergent lenses, and therefore of the simple micro- 

 scope, however small the enlargement by his lenses may have been. 

 As, however, that man of rare genius, the initiator of experi- 

 mental physics, had brought on himself the 

 hatred of his contemporaries, they kept him 

 for many years in prison, then shut him up 

 in a convent of his order to the end of his 

 long life of nearly eighty years. His writings 

 had to be hidden, at least those treating on 

 natural science, to save them from destruc- 

 tion, and so the invention of lenses, or the 

 knowledge of their use to enlarge images and 

 to alleviate the infirmities of sight, remained 

 unknown or forgotten in the pages of the 

 famous ' Opus Majus,' which only came to 

 light in 1733 by the care of Samuel Jebb, a 

 learned English doctor. 



A Florentine, by name Salvino degli 

 Armati, at the end of the thirteenth century 

 (? 1280) (in Bacon's lifetime), had therefore 

 the glory of inventing spectacles, and it was 

 a monk of Pisa, Alexander Spina, who sud- 

 denly charitably divulged the secret of their 

 construction and use. 



Perhaps Salvino degli Armati and Spina 

 really discovered more than Roger Bacon had 

 discovered ; that is, they found out the use 

 of converging lenses for long-sighted people, and of diverging lenses 

 for short sight, whilst the English monk had only spoken of the 

 lenses for long sight, and perhaps they added to this first inven- 

 tion the capability of varying the focal lengths of the lenses accord- 

 ing to need, and the other of fixing them on to the visor of a cap to 

 keep them firm in front of the eyes, or to fasten them into two, 

 circles made of metal, or of bone joined by a small elastic bridge 

 over the nose. However it may be, the discovery of spectacles, or, 

 as it may be called, of the simple microscope, may be equally divided 

 betwen Roger Bacon and Salvino degli Armati, leaving especially to 

 the latter the invention of spectacles. 



The earliest known illustration of a simple microscope is given 

 by Descartes in his ' Dioptrique' in 1637 : fig. 91 reproduces it. It 

 is practically identical with one devised by Lieberkiihn a century 



FIG. 91. Descartes' simple 

 microscope with reflector 

 (1687). 



