Wrote Letter 41 of 1684-04-14 (AB 80) to Francis Aston about lenses and corneas, the function of eye-lids, the involuntariness of blinking, the optic nerve, and the skin of Moors

April 14, 1684
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Text of the letter in the original Dutch and in English translation from Alle de Brieven / The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren.

The original manuscript, written and signed by Leeuwenhoek, is preserved at the Royal Society (MS. 1900. L 1. 71.).


The original drawings are lost. The nine images appeared on five plates. Below are the two plates with multiple figures. Figs. 7, 8, and 9 are directly below the enlarged Fig. 6 to show the proportion.

Plate from
Arcana Naturae Detecta

Figures 4-5

Figures 6-9

In Humor Cristallinus, the figures are placed in the next close to Leeuwenhoek's discussion of them. In the 1695 first edition of Arcana Naturae Detecta, from which the images on the sidebar came, Figures 3 and 6 were reversed.

The following quotations from the Alle de Brieven / Collected Letters translation of the manuscript note who made the drawings. He drew Figures 1, 2, and 3. Because he must have had tools to help him make the circles and parallel lines, he may have used ink instead of red chalk. An unnamed goet tekenaar (good draftsman) drew Figure 4. Leeuwenhoek drew Figures 5 and 6. He did not say who drew Figure 7, but it was probably Leeuwenhoek.

I further observed that each of these scales consists of fibres lying side by side in very neat arrangement, so that each scale is one fibre thick. In order to show distinctly the fibrous substance of the crystalline body I have indicated it as well as I could by lines drawn in a circle.

Figure 1:

Fig. 1 ABC represents the crystalline body, as large as it appears to our naked eye. B is turned towards the cornea through which the sight or the light passes. This I have magnified that I might more distinctly show the fibres of which each scale consists.

Figure 2:

Fig. 2 KEFGHIL is here drawn as if the preceding fig. 1 with the round part B lay directed toward the eye; and although I have drawn or shown many lines (representing fibres) in the afore-said body.

Figure 3:

And in order to have this more distinctly before our eyes I have drawn the fibres, forming a scale of the crystalline body and seen sideways, by means of lines, as in fig. 3 RTPSWQ; and although it is a flattish round, I have here made it a perfect round, my reason for this being that in this manner one can better show the said fibres of which each scale consists.

Figure 4:

First I roughly drew the fibrous character of each scale with red chalk on paper, and then showed it through a magnifying glass to a good draughtsman and ordered this draughtsman to draw it as accurately as possible. But because, in my opinion, the fibres here represented, are drawn too close together and cannot be well distinguished, I also send you the figures in red chalk, although the draughtsman said that all would be much more distinct when engraved on a plate than in his drawing.

Figure 5:

I have also drawn it as seen from one side, in order to be able to show more distinctly the fibrous substance of each scale.

Figure 6:

Fig. 6 ABCD represents the crystalline body of a cod's eye; and although I have only drawn the curved lines (representing the fibres of which each scale consists) with a pair of compasses, from the centre or point A up to the centre C.