440 HISTORY OF LENSES AND MICROSCOPES [Cn. XII 



bringing out the images. You can draw on the paper with a pencil all the perspective, 

 and the shading and coloring according to nature." 



705b. Johannes Kepler. In Reliquiae Wottonianae, edited by Izaak 

 Walton, London, 1672 pp. 298-300. In a letter to his kinsman, Francis Bacon: 

 "I have your Lordship's letters dated the 2oth of October (1620). I lay a night 

 at Lintz . . . there I found Kepler, a man famous in the sciences, as your Lord- 

 ship knows, to whom I purpose to convey from hence one of your books [Novum 

 Organum], that he may see we have some of our own that can honor our king as 

 well as he has done with his Harmonica. 



In this man's study I was much taken with a draught of a landskip on a piece 

 of paper, me thought masterly done; whereof enquiring of the author, he bewrayed 

 with a smile, it was himself; adding he had done it, non tanquam pictor, sed tan- 

 quam mathematicus [not as an artist but as a mathematician]. This set me on 

 fire: At last he told me how. He hath a little black tent (of which stuff it is not 

 much importing) which he can suddenly set up where he will in a field; and it is 

 convertible (like a windmill) to all quarters at pleasure, capable of not much more 

 than one man, as I conceive, and perhaps at no great ease; exactly close and dark, 

 save at one hole, about an inch and a half in diameter, to which he applies a long 

 perspective trunk [Dutch Telescope] with the convex glass fitted to the said hole 

 and the concave taken out at the other end, which extendeth to about the middle 

 of this erected tent; through which the visible radiations of all the objects without 

 are intromitted, falling upon a paper which is accommodated to receive them; and 

 so he traceth them with his pen in their natural appearance, turning his little tent 

 around by degrees till he hath designed the whole aspect of the field. This I have 

 described to your Lordship because I think there might be good use made of it 

 for chorography; for otherwise to make landskips by it were illiberal, though 

 surely no painter could do them so precisely." 



706c. Henry Baker. The Microscope Made Easy, 1742. On page 25 occurs 

 this: "Such too as have no skill in drawing may, by this contrivance, [projection 

 microscope], easily sketch out the exact figure of an object they have a mind to 

 preserve a picture of; since they need only fasten a paper upon a screen and trace 

 it out thereon either with a pen or pencil as it appears before them." 



705d. Dark -field microscopy. The ancient opticians appreciated as keenly 

 as we at the present day, that the principle of contrast was of the highest import- 

 ance in rendering objects visible; but before this could be applied to the micro- 

 scope, the instrument itself must be invented (1590-1611); and then must follow 

 the perfecting of all the optical parts and the invention of a reflecting condenser 

 (1850-1856), and the working out of the immersion principle to its culmination in 

 the homogeneous immersion objectives of Tolles (1871-1874). For artificial light 

 the arc lamp of Davy (1800) and the Mazda lamps of our own time were needed, 

 and finally the Daylight Glass to protect the eyes and clarify the image. 



In glancing backward over the long road which has been traversed in arriving at 

 the present stage with optical instruments, there are two causes for astonishment: 

 First, that mankind was so late in discovering the laws of refraction, and then their 

 application for the production of lenses and their combination into optical instru- 

 ments; and secondly, the almost fabulous progress that has taken place since the 

 first possibilities of lenses were discovered some six hundred and fifty years ago, 

 and especially during the last three hundred and fifty years since the combination 

 of lenses to make the compound microscope and the telescope was found out. 



