582 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to mention emeralds (?) four cubits long and three wide, and others 

 larger still mentioned, although, doubtfully, by Pliny and Theophrastus. 



We must, however, note that the ancients confounded many different 

 stones under the name of emeralds, and who knows how often they may 

 have also given the name of emeralds to glass tinted a beautiful green, 

 as the sacred basin in green glass in the possession of the Genoese was 

 believed to be and is still reputed by many an emerald. The Genoese 

 obtained it in 1102 frona Cesarea, where it passed for the cup of 

 Christ's Last Supper. 



The ancients therefore had no lenses either convex or concave, or at 

 least no document is extant to show that they had any or knew how to 

 use them. 



With the decadence of the Roman power the arts and sciences fell 

 also, and when the seat of the Empire passed from Eome to Constanti- 

 nople, night fell on the intellectual world, and the nations tossed in a 

 long and fearful sleep, during which only torments and prodigies were 

 invented. 



The beginning of the middle ages was really the age of darkness, 

 but after the year 1000 minds having reopened to hope and intellects 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,' dedi- 

 cated and presented by him to Clement IV., (26) 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 sufficiently enlarged, how- 

 ever small tliey are." As long as no documents anterior to him are 

 discovered, Roger Bacon may be considered the first inventor of con- 

 vergent lenses, and therefore of the simple Microscope, however small 

 the enlargement by his lenses may have been. 



As, however, that man of rare genius, the initiator of experimental 

 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 destruction, 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 life-time), had therefore the glory 

 of inventing spectacles, and it was a monk of Pisa, Alexander Spina, who 

 suddenly charitably divulged the secret of their construction and use. 



Perhaps Salvino degli Armati and Spina really discovered more than 

 Roger Bacon haJ discovered ; that is, they found out the use of converg- 

 ing 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 invention the capability of 

 varying the focal lengths of the lenses according 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 



