THE MICROSCOPE. lo^ 



lenses, each pair in turn consisting of a double convex glass, and 

 four years later Arnica, of Modena, produced an achromatic com- 

 bination surpassing anything previously constructed in this line; 

 and from that time on the principle of combining two or more 

 lenses so shaped and adjusted as to correct each other's errors was 

 firmly established. * * * * j-q ^^g discoveries of 

 Joseph Jackson Lester and their practical application by working 

 opticians, like Andrews, Ross and Smith, of London, we owe the 

 production of compound objects of wide aperture, flatness of field, 

 and above all of highly perfected definition. * * * * 



Then followed in rapid succession improvement upon improvement; 

 the immersion principle was utilized [Amici-Hartnack]; the aberra- 

 tion produced by the cover-glasses corrected [Ross] ; the angle of 

 aperture increased to 135 degrees, which for a long time was held 

 to be the largest attainable, etc., etc. Meanwhile, there had grown 

 up, in a little village of this state a young man of a scientific and 

 practical turn of mind who had taken for himself and by himself the 

 study of optics and had even in his boyhood made with his own 

 hands a microscope and some telescopes, and later on had done, 

 though without much encouragement or patronage, good work as a 

 microscopist, too. Reading Ross' paper, and not feeling satisfied with 

 his theoretical reasoning, he soon brought forth practical proof of 

 the correctness of his own instincts by manufacturing a dry one-inch 

 and one-twelfth inch objectives of 146° aperture. This young man 

 was Charles A. Spencer, the father of American microscopy, 

 and, I am glad to say, the first honorary member of this 

 society. Soon after, Professor Bailey, of West Point academy, suc- 

 ceeded in resolving with one of young Spencer's microscopes the 

 markings on a diatom which had resisted the best objectives of for- 

 eign make which he had been able to procure. Bailey was of 

 course delighted, and named the little creature Navicula Spencerii. 

 * * * * In the meantime the improvement of the 

 microscopes had been progressing rapidly in other directions also. 

 Thus, the negative eye- piece was adapted from the telescope to our 

 instrument. The " stand " also began to receive much attention, 

 particularly in England, where great pains were taken to make it 

 solid and steady, yet handy and provided with many useful accesso- 

 ries. Indeed, to such an extreme were these efforts carried in some 

 cases that the more costly stands a few years ago, were ponderous 



