Ch. XII] HISTORY OF LENSES AND MICROSCOPES 425 



lenses and the optical instruments which they make possible. But 

 what immeasurably greater insight into the real world has come with 

 these " optic glasses"! What revelations as to the cause of disease, 

 of the structure of the universe in its smallest details by the micro- 

 scope, and in its larger ranges by the telescope; and greatest of all 

 for the common man, has come the power, by means of spectacles, to 

 make good use of the years that hygiene has added to the average 

 human life. 



That nature made lenses during every rain-storm and every heavy 

 dew and in the tears of every gum and balsam tree, we know now; 

 and for the almost infinite years which man has been upon the earth, 

 the learned and the ignorant were equally unmindful of the marvel 

 before their very eyes; as unmindful as are the vast majority of men 

 and women at the present day. 



All who have made a study of the question are unanimous in the 

 opinion that optical instruments, other than mirrors, were unknown 

 to the ancient world; and that lenses were wholly unknown. Some, 

 however, find in the disc of quartz in the British Museum and known 

 as the Assyrian " lens," and dating from about 700 B.C., evidence 

 that lenses were made before the Christian era. How one who actually 

 sees this disc of quartz can think of it as a lens is inconceivable to me. 

 Mayall, who had an opportunity to study it, decides wholly against 

 the lens theory. In his work on the history of the microscope, p. 5, 

 he gives a face and an edge view of it. 



In the first and second centuries of the Christian era there was an 

 abundance of knowledge of mathematics and of optics to make possi- 

 ble the invention of the simple microscope and of appreciating it as 

 such. In works of literature there are hints that men were on the 

 track. For example, Seneca, in his Questiones Naturales (L. 1, q. 6), 

 says that " Letters however small and dim are comparatively large 

 and distinct when seen through a glass globe filled with water." and 

 that apples in a vase of water are far more beautiful. He is trying to 

 account for the size of the rainbow and sums it all up by saying that. 

 "anything, in fact, that is seen through moisture appears far larger 

 than in reality it is." To Seneca the magnification was the effect of 

 the water and not the effect of the refraction at curve! 1 surfaces, 



