56 THE EARLIEST STEPS IN THE INVENTION OF 



(5) John Peckham (died 1292), Archbishop of Canterbury, was 

 the author of a work on optics entitled Persyectiva communis. His 

 views were very similar to, and, perhaps, taken from. Bacon. He 

 is important only as having drawn wide attention to optical prin- 

 ciples. His work exists in a number of manuscripts, and has often 

 been printed. The first edition is dated from Milan, 1482. 



(6) The names of Salvino d'Amarto degli Amarti of Florence 

 and Alessandro de Spina of Pisa (both circa 1300) have become 

 associated with the special application of lenses for use as spectacles. 

 Lenses, as we have seen, were known to Roger Bacon, who suggested 

 also their use in aiding vision. D'Amarto and Spina applied the 

 principle thus suggested. From about 1300 onward convex lenses 

 for use as spectacles were well known, 



. The question of the invention of spectacles has been frequently 

 discussed. One of the latest writers who has traversed this field 

 is V. Rocchi, Appunti di storia critica del microscopio, in the 

 Eevisfs di Storia critica delle Scietize Mediche e Xatiirali, January, 

 1913. 



(7) Leonardo da Vinci (1452-1519) had sounder ideas than any 

 of his predecessors on the structure of the eye, on binocular vision, 

 on refraction and diffraction. He developed a practical camiera 

 ohsciua, and gives a hint of a '' glass to see the moon enlarged." 

 His work, though original and valuable, remained inaccessible for 

 nearly four centuries, and had no influence on his contemporaries. 



Leonardo left his scientific remains in a state of confusion, and 

 they have suffered much by time and misuse. It is impossible to 

 give a bibliography here, but his optical results are summarised by 

 E. Solmi, Leonardo da Vinci e il tnetodo sperimentale nelle ricerche 

 fisiche, in the Atti e niemorie della R. Accademia Virgiliaiio di 

 Mantova, Mantua, 1905, and by O. Werner, Zur Physik Leonardo 

 da Vincis, Berlin, 1911. 



(8) Girolamo Fracastoro (1478?-1553) was a suggestive writer 

 who devoted considerable space to a rather confused account of 

 refraction. In the course of this discussion he has the following 

 passage: — " (Not only the character but) also the position of the 

 medium affects the appearance of the objects seen, as may be observed 

 with spectacle lenses {in specillis ocularihus). For if the lens be 

 placed midway between eye and object, it appears much larger 

 than if the lens is made to approach the object or the eye. {//omo- 

 centrlca II, 8). . . . Glasses {xpecUla ocularia) may be arranged 

 of such density that if anyone looks through them at the moon or 

 at any star they appear near and hardly higher than the steeples. 

 {Ilomocentrica, III, 23)." It is possible that he was here con- 

 templating a bilenticular apparatus. The TI oworentrica in which 

 these passages occur was first printed at Venice in 1538. The 

 scientific value of this work is discussed by the present writer in an 

 article in the Arnuds of Mfdicfd Ilixtori/, Vol. I, p. 1, New York, 

 1917. 



