Visited by James, Duke of York, and "several high personages"

May 1, 1679

On October 13th 1679, Leeuwenhoek wrote to Hooke (AB 51):

His Highness the Duke of York honoured me a few days before his departure from this country by a visit, accompanied by several high personages. He wished to see my simple observations and so I showed His Highness among other things, the little animals in the male sperm of a dog through an ordinary microscope. His Highness admitted that he not only saw that they lived, but that he even could clearly distinguish their tails.

James was in the Republic for only a couple of weeks in the fall of 1679. His biographer E. C. Turner wrote (1948, p. 168):

On September 24 [James] was on his way back to Brussels to rejoin the Dutchess and to make arrangements for his departure to Scotland. He made the same time as he had taken on the homeward journey, and he was in Brussels on the 27th, and he took so short a time over his preparations there that he was at The Hague with Mary Beatrice five or six days later. There he found ships to convey his retinue and belongings to Scotland, and he embarked, after bidding farewell to his daughter and son-in-law for the last time. ... They eventually arrived in London on October 14.

In a letter to his son Christiaan on May 4, 1679, (Oeuvres complètes, letter 2167) Constantijn Huygens indicated that the Duke visited Leeuwenhoek not long before that date, seeming to contradict Turner.

The dutchess, Maria Beatrice Anna Margherita Isabella d'Este (1658-1718), the daughter of Alfonso IV, Duke of Modena, was James’ second wife.

They went to The Hague before leaving because it was the home of Mary Stuart, James' oldest surviving child. Her husband, William of Orange, was Stadhouder of the Dutch Republic. They succeeded him on the throne in 1688.

Before that, in 1687, Leeuwenhoek dedicated Anatomia seu interiora rerum, a collection of his letters in Latin, to James, then James II, King of England.