were others, fortunately, who did not despair of the
possibilities of the refracting microscope, and their efforts
were destined before long to be crowned with a degree of success
not even dreamed of by any preceding generation.

The man to whom chief credit is due for directing those final
steps that made the compound microscope a practical implement
instead of a scientific toy was the English amateur optician
Joseph Jackson Lister. Combining mathematical knowledge with
mechanical ingenuity, and having the practical aid of the
celebrated optician Tulley, he devised formulae for the
combination of lenses of crown glass with others of flint glass,
so adjusted that the refractive errors of one were corrected or
compensated by the other, with the result of producing lenses of
hitherto unequalled powers of definition; lenses capable of
showing an image highly magnified, yet relatively free from those
distortions and fringes of color that had heretofore been so
disastrous to true interpretation of magnified structures.

Lister had begun his studies of the lens in 1824, but it was not
until 1830 that he contributed to the Royal Society the famous
paper detailing his theories and experiments. Soon after this
various continental opticians who had long been working along
similar lines took the matter up, and their expositions, in
particular that of Amici, introduced the improved compound
microscope to the attention of microscopists everywhere. And it
required but the most casual trial to convince the experienced
observers that a new implement of scientific research had been
placed in their hands which carried them a long step nearer the
observation of the intimate physical processes which lie at the