LEEUWENHOEK, or LEUWENHOEK, ANTHONY VAN. one of the earliest microscopic observers, was b. at Delft, in Holland. in 1632, and d. in the same town in 1723. The com pound microscope, as it existed in his time, was very imperfect, and subject to many errors. which induced Leeuwenhoek to employ only simple microscopes, that is to say, very small lenses of short focal lengths, which were fixed between two plates of metal that had been pierced with a very narrow opening. He bequeathed to the royal society of London (where they are carefully preserved) a collection of these microscopes. It was in the Philosophical Transactions of this society, to which he contributed 112 papers, that most of his observations were originally published.
Amongst the most important of his investigations may be mentioned a memoir com municated to the royal society in 1690, in which he discovered, and clearly demon strated, the continuity of the arteries and veins through intervening capillaries. and
thus afforded ocular demonstration of the truth of Harvey's views regarding the circula tion; lie also examined the structure of the crystalline lens and of the brain. He is, perhaps, most generally known as the discoverer of the rotifers, and as being the first to recognize the property which these animals possess of alternately dying and being resuscitated, according as they are dried or provided with the water necessary for the maintenance of their vitality.
His writings were collected and published in Dutch at Leyden and Delft in seven 4to vols., the publication extending from 1686 to 1732. A Latin translation, under time title of Opera Omnia sea Areana "'Nature, was published at Leyden in 1792; and an English translation was published by Mr. Samuel Hoole, in two 4to vols., in 1798-1800.