Gottfried Leibniz wrote to Hendrik van Bleyswijk about the need for Leeuwenhoek to train students in order to render "even greater services to the human race"
The date is New Style, which was ten days ahead of the Old Style date of 27 April 1697 used by Leibniz in Hanover.
In this letter to Bleyswijk, Leibniz initiates their discussion of whether Leeuwenhoek should take on students. Leibniz saw it as almost a moral imperative, to "render even greater services to the human race to make the interior of nature better known".
He wrote another letter to Bleyswijk on this same topic on 3 January 1698. Bleywijk responded to both letters. Almost two decades later, Leibniz addressed the topic directly with Leeuwenhoek, who explained why he did not think it was worth his while to train students.
Leibniz-Akademie-Ausgabe, Band I, 14
Leibniz's original French:
Voyant que vostre lettre est datée de Delpht, je ne sçaurois m’empecher de dire que vous y avés un homme merveilleux, dont j’eus hier l’honneur de parler chez Mad. l’Electrice, apres Mons. Hop. Il luy est glorieux à Mons. Leewenhoeck d’estre seul et comme unique de son espece. Mais cela n’est pas avantageux pour le public qui auroit besoin de plusieurs observateurs sembla bles à cause de l’etendue de la nature qu’un seul ne sçauroit assés observer quand il auroit les yeux d’Argus.
S’il avoit auprés de luy des jeunes gens capables de l’assister, et de suivre, et même de pousser ses lumieres, il iroit incomparablement plus loin, et rendroit des services encor plus grands aux genre humain pour mieux faire connoistre l’interieur de la nature. Mais il faudroit l’encourager pour cela. Des-Cartes et d’autres qui ont voulu parler de la composition des corps sensibles, n’ont donné que des conjectures, qui le plus souvent se trouvent fausses. Au lieu que M. Leewenhoek nous apprend des choses seures. [On croit que nous devons les lunettes de longue veue à la ville de Middelbourg, et par consequent nous luy sommes redevables en partie de toutes ces merveilles qu’on a decouvert depuis dans le ciel; je trouve que nous ne serons pas moins redevables à vostre ville d’une connoissance plus exacte des choses qui nous touchent de plus prês; et qui pourront servir dans la Medicine et dans les arts, si la Methode de Mons. Leewenhoek est poursuivie.]
Il ne doit plus estre jeune car il y a environ 20 ans, quej’ay vû son cabinet. Ainsi il me semble que le public est interessé à la conservation de sa science, et doit penser à luy donner des heritiers capables de faire valoir d’avantage un jour le fonds qu’il a acquis. C’est à dire il faudroit le faire savoir à avoir des bons éleves. On peut rendre service au public et à la posterité dans les sciences et faire honneur à son pays en differentes manieres. Les uns comme inven teurs, les autres comme observateurs qui sont comme les aides des premiers. Les inventeurs tels que Mons. Hugens ou Mons. Hudde, par la superiorité de leur genie et par la force du raisonnement ont trouvé des secrets où les sens ne sçauroient atteindre; et des excellens observateurs tels que M. Leewenhoek, nous font voir ou sentir par leur diligence et par leur industrie, ce qui avoit échappé aux yeux des autres. Et j’estime plus un tel homme, que le plus excellent peintre, fust ce Raphael luy même, malgré tout l’entestement des Italiens.
Poor Google translation:
Seeing that your letter is dated Delft, I cannot help saying that you have a marvelous man there, of whom I had the honor of speaking yesterday at Mademoiselle the Electress, after Mons. Hop. He is glorious in Mons. Leewenhoeck to be alone and unique of his species. But this is not advantageous for the public who would need several similar observers because of the extent of nature that only one could not observe enough when he had the eyes of Argus.
If he had near him young people capable of assisting him, and of following, and even of pushing his limits, he would go incomparably further, and render even greater services to the human race to make the interior of nature better known. But he should be encouraged for that. Descartes and others who wanted to talk about the composition of sensible bodies have only given conjectures, which most often turn out to be false. Instead, Mr. Leewenhoek teaches us certain things. [It is believed that we owe the long-sightedness glasses to the city of Middelburg, and therefore we are indebted to them in part for all the marvels that have since been discovered in the sky; I find that we will be no less indebted to your city for a more exact knowledge of the things that affect us most closely; and which can be used in medicine and in the arts, if the method of Mons. Leewenhoek is being prosecuted.]
He must not be young anymore because I saw his office about 20 years ago. Thus it seems to me that the public is interested in the preservation of his science, and must think of giving it heirs capable of making better use one day of the funds it has acquired. That is to say it should be known to have good students. One can render service to the public and to posterity in the sciences and do honor to one's country in various ways. Some as inventors, others as observers who are like the helpers of the first. Inventors such as Mons. Huygens or Mons. Hudde, by the superiority of their genius and by the force of reasoning, have found secrets where the senses could not reach; and excellent observers such as Mr. Leewenhoek make us see or feel by their diligence and industry, what had escaped the eyes of others. And I esteem such a man more than the most excellent painter, was this Raphael himself, despite all the stubbornness of the Italians.