Antonie van Leeuwenhoek

Antonie van Leeuwenhoek (October 24, 1632 to August 26, 1723) was a Dutch cloth merchant and city official in Delft who ground his own single-lens microscopes and described what he saw through them in letters to the Royal Society of London. His name appears in the sources as Antony, Antoni and Antonie. He had no university training and wrote in Dutch, the only language he knew.^[1] His letters report bacteria, single-celled animals he called animalcules, and the spermatozoa of mammals, and Clifford Dobell titled his 1932 biography of him a study of "the father of protozoology and bacteriology".^[2] The Royal Society elected him a Fellow in 1680.^[2]

He kept his methods secret, would not sell his microscopes while he lived, and left more than 500 instruments and lenses at his death. Ten microscopes with a credible claim to be his are known today.^[3] Almost everything else he made is gone, including the cabinet of 26 silver-mounted lenses that he bequeathed to the Royal Society.^[2]

Leeuwenhoek was born in Delft and baptized on November 4, 1632. His father, a basket-maker, was buried in January 1638, and in 1648 he was apprenticed to a draper in Amsterdam. By about 1654 he had a drapery and haberdashery of his own in Delft, and on July 29 of that year he married Barbara de Meij. Their daughter Maria, born in 1656, outlived him. Barbara died in 1666, and on January 25, 1671 he married Cornelia Swalmius.^[2]

Municipal posts came to him alongside the shop. He was appointed chamberlain to the sheriffs of Delft on March 26, 1660, surveyor on February 4, 1669, and wine-gauger of the city on August 15, 1679.^[2] On September 30, 1676, about nine months after the painter Johannes Vermeer was buried in Delft, he was appointed curator of the estate of Vermeer's widow, Catharina Bolnes. In February 1677 he recovered 26 paintings to help pay her creditors, and in March he organized an auction of the remaining pictures. The widow's mother went to law to stop him selling one of them, The Art of Painting.^[4]

On April 28, 1673 the Delft physician Reinier de Graaf wrote to Henry Oldenburg, the secretary of the Royal Society, about a man in his town who had devised microscopes that "far surpass" those of the Italian maker Eustachio Divini and others. England and the Dutch Republic were at war, and de Graaf opened by saying that learning had not been banished from the country "by the clash of arms". With the letter came a first specimen of Leeuwenhoek's observations on mould, on the sting, mouthparts and eye of the bee, and on the louse. Oldenburg printed them in Philosophical Transactions that May with a remark Dobell calls somewhat sardonic: that the observer would no doubt go on sending more, "the better to evince the goodness of these his Glasses".^[2][5]

Leeuwenhoek went on writing for half a century. A modern census counts 285 letters with scientific observations, of which 189 went to the Royal Society or its officers to be published. A little over half were illustrated, with more than 1,200 figures in all, and he published 165 of the letters himself in Dutch and in Latin translation. The Royal Society's journal printed extracts from them in 117 articles.^[1] A translation of his letter of October 9, 1676 on "little animals" in rain, well, sea and snow water, and in water in which pepper had lain, appeared on March 25, 1677.^[6]

The Society doubted the animals. Robert Hooke, who had published Micrographia in 1665, was asked to look for himself with better microscopes. At the meeting of November 15, 1677 (Old Style) he showed pepper-water in which he had found "exceedingly small animals swimming to and fro", and the Fellows who saw them "verily believed" them to be animals, "and that there could be no fallacy in the appearance".^[2][a]

In a letter of September 17, 1683 to the Royal Society's secretary he described scraping the white matter from between his teeth, mixing it with rain-water, and seeing "with great wonder" that it held "many very little living animalcules, very prettily a-moving". The largest kind, he wrote, shot through the water "like a pike does through the water". In the same letter he recalled that several women visitors had been so disgusted by the little eels in vinegar that they vowed never to use vinegar again, and asked what they would say if told that there are more animals living in the scum on the teeth in a man's mouth than there are men in a whole kingdom.^[2] Dobell dates his discovery of protozoa to 1674 and of bacteria to 1676.^[2]

The spermatozoa had a co-discoverer. In 1677 Johan Ham, a medical student from Arnhem who had studied at Leiden, brought him a specimen to examine under his lens. They found spermatozoa, and Leeuwenhoek reported them to the Royal Society in a letter to Lord Brouncker dated November 1677.^[7] Dobell calls Ham the co-discoverer.^[2] Nicolaas Hartsoeker, who had visited Leeuwenhoek with his father, went to Paris and tried to claim the discovery as his own, and Dobell says he did not succeed.^[2] The French Académie des Sciences named Leeuwenhoek a correspondent on March 4, 1699.^[2]

Leeuwenhoek's microscope had a single lens, a glass bead a millimetre or two across, held between two brass or silver plates, with the specimen on a needle that threaded rods moved for coarse and fine focus. The high curvature of so small a lens gives a very short focal length, and the instrument had to be held extremely close to the eye. The Whipple Museum in Cambridge gives his magnifications as 20 to 275 times and notes that the microscopes were hard to use, as contemporaries remarked.^[8] Examples shown by the Lens on Leeuwenhoek project range from 68 to 266 times.^[9]

He did not explain how he made his lenses. A German jurist, Zacharias Conrad von Uffenbach, visited him with his brother on December 4, 1710 and found his cabinet to contain at least a dozen lacquered boxes holding some 150 cases, each with two microscopes. Leeuwenhoek told them he would sell none in his lifetime. He said the lenses were all ground in the same grinding-cup and showed contempt for blown glass; when pressed, he added that after ten years' thought he had learned to blow a serviceable lens that was not round, which Uffenbach's brother took for "a Dutch joke". He also scratched his own arm with a penknife, collected the scrapings on a glass tube and showed the visitors what he took to be scales. Uffenbach thought they were scurf.^[2]

In a letter of 1701 he described the cabinet that he intended for the Royal Society: a small black lacquered case with five drawers holding 13 tin cases, each with two lenses, "every one of them ground by myself", mounted in silver, "almost all of them in silver that I extracted from the ore". It was sent by his daughter Maria on October 4, 1723, after his death. The Society kept it for a century and then lost it, and sent Maria in return a silver bowl bearing its arms.^[2] At his death he left more than 500 simple microscopes, eel viewers and lenses, and only ten microscopes with a credible claim to be his survive.^[3] The rest were sold on May 29, 1747, two years after Maria's death.^[2][10]

In 1716 the professors of a college at Louvain sent him a silver medal with his bust on it. In his reply of June 12 he wrote that his work had been done "chiefly from a craving after knowledge, which I notice resides in me more than in most other men".^[2] He was buried in the Old Church in Delft on August 31, 1723, "with 16 pall-bearers and with coaches and tollings of the bell".^[2]

In 1827 Robert Brown made the observations that gave Brownian motion its name with a simple microscope and a single lens of about one thirty-second of an inch focal length, as Leeuwenhoek had used.^[11] The twenty volumes of Alle de Brieven, the complete collected letters, can be downloaded free from the Lens on Leeuwenhoek website.^[1]

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