ABSTRACT
As has been previously pointed out, microscopical research had a period of brilliant success in the seventeenth century, the age of Malpighi and Leeuwenhoek. Afterwards, however, this method made no further advance for more than a hundred years; the eighteenth century certainly produced some microscopists of importance, such as, for instance, Lieberkühn, but on the whole little was achieved during this period with the aid of magnifying apparatus. The reason for this was that the aforesaid scientists of the seventeenth century and their contemporaries did all that could be done with the instruments at their disposal; microscopes were and remained imperfect, and improvements were a long time in coming. The most serious difficulty lay in the chromatic aberration of the lenses; a colourless object seen under the microscope would shimmer with all the colours of the rainbow, a fact which naturally gave rise to countless misinterpretations of the objects investigated. To procure achromatic glass, free from this fault, was a task that occupied many scientists at that time; Newton himself declared the problem to be insoluble. Eventually a Swede, Samuel Klingenstierna (1698-1765), professor of physics at Upsala, succeeded in working out how the achromatic glass should be made, and under his instructions an English mechanician, Dollond, constructed the first achromatic lenses. It was some time, however, before the invention could be utilized for microscopical purposes. Among those who in the beginning of the nineteenth century constructed microscopes with achromatic lenses may be mentioned the Frenchman Chevalier and the Italian Amici; the latter's microscopes in particular were very fine, and there soon arose in every country microscope-makers who produced gradually perfected instruments. The year 1817 is named as that in which Amici demonstrated his first achromatic lens-system and during the thirties the biological institutions, at least the more important ones, were able to obtain specimens of these improved microscopes. It was at the beginning of that decade also that microscopical biology first showed any notable advance, and after that the great discoveries in this field followed one another in rapid succession.
