The theories propounded about this time for the improvement of lenses and the various combinations for amateurs were not of lasting value. Nevertheless, they were not wholly made in vain, as during the last twenty years they have indirectly borne good fruit, inasmuch as by working in another direction Professor Abbe was led to the discovery of new and better kinds of glass, by which the secondary spectrum has been so nearly eliminated, and the optical parts of the microscope so materially improved. In pursuing this subject I would not have it supposed that Continental opticians were either idle or supine. On the contrary, Oberhäuser, Fraunhofer, Chevalier, Nachet, Hartnach, and others took an active part in the work. The compound microscope made for anatomists by the first-named optician about 1825 has not been entirely superseded. He was the first to make a rotating stage, to apply mechanism to focussing, and to introduce the system of direct push or pull of the condenser tube within the sub-stage socket. Nachet made other improvements on the Oberhäuser microscope by applying under the stage a tail-piece having a dove-tailed groove in which a slide carrying the sub-stage was moved by a stud-pin. More recently the lever movement was superseded by American opticians, who made other changes. Hartnach ultimately very much improved Oberhäuser’s model, and this remains with us. The English modern compound microscope, together with the achromatic objective, we owe to a mind teeming with scientific inventions, Joseph Jackson Lister, F.R.S., who in 1826 supplied Mr. Tully, a well-known London optician of that period, with original drawings for the important improvements in its mechanical details and accessory apparatus which followed so soon afterwards.