Hooke's Three Tries

October - November 1677

Robert Hooke, of whom no painted portrait survived, was a man of many interests and talents, not the least of which was drawing. He had paid some attention to the microscope when he published his groundbreaking and best-selling Micrographia in 1665. Its drawings, some of which were oversized foldouts, made it a best seller.

October 15 Royal Society requests Hooke to make a microscope powerful enough to replicate AvL's observations.
November 1 Hooke, using thinner pipes, fails to demonstrate "minute animals".
November 8 Hooke, using even thinner pipes, fails again to reveal "Mr. Leewenhoeck's animals".
November 15 Hooke finally succeeds in showing "great numbers of exceedingly small animals swimming to and fro. ... so that there was no longer any doubt of Mr. LEEWENHOECK'S discovery."

Other events then occupied his time. He helped Christopher Wren, another Royal Society charter member, rebuild London after the Great Fire of 1666. As Curator of Experiments for the Royal Society, he turned his mind to a wide array of scientific claims in what we now call physics, chemistry, and biology. For years, he devised experiments to replicate these claims at the Society's weekly meetings.

In the fall of 1677, Hooke turned his mind back to microscopy. The members asked him to do what they had, the previous spring, asked Nehemiah Grew (left) to do: show the members of the Society the vast number of little animals that Leeuwenhoek was claiming to see. Grew had not succeeded, so now it was Hooke's turn.

First try: "no discovery made"

At the meeting of November 1, 1677 (emphasis added):

There were produced a great many exceedingly small and thin pipes of glass of various sizes, some ten times as big as the hair of a man's head; others ten times less. These were made in order to try a conjecture of Mr. HOOKE, propounded to the Society, that the discoveries, affirmed to be made by Mr. LEEWENHOECK, were made by help of viewing with a good microscope such small pipes containing the liquor or water, in which those multitudes of exceedingly small insects or animals wriggling among each other are discovered;

for that he alledged, that the said pipes being filled with liquors became themselves as it were magnifying glasses, augmenting such bodies, as swim in the said liquor, on those parts of the said pipes, which are farthest from the eye-glass;

for the pipes themselves being looked on by the help of a very good microscope, are made very large and conspicuous; and they again augmenting the opposite parts by the refraction on their cylindrical surfaces double the effect of a single microscope, as was very evident.

But notwithstanding this there was no discovery made in the liquor, that was made use of, which was only common pump-water, of any such minute animals.


According to Birch's History, Hooke's replication of Leeuwenhoek's observations was witnessed by nine named members and "various others". The two most historically prominent, Christopher Wren and Nehemiah Grew, are mentioned elsewhere on this web. In addition:

Thomas Henshaw
Founder Fellow of the Society

Sir John Hoskins, Bart
fellow 1674
president 1682-1683
also spelled Hoskyns

Abraham Hill
Founder Fellow 1663
secretary 1673-1675
treasurer 1679-1700

John Mapletoft
clergyman and physician
Fellow 1676
member of council 1677, 1679, 1690, and 1692

Jonas Moore
mathematician, surveyor, Ordnance Officer and patron of astronomy
Fellow 1674

William Croone
Founder Fellow 1663
nominated Leeuwenhoek for election as Fellow in 1680
also spelled Croune

John Aubrey
antiquary and writer
Founder Fellow 1663

Using a single-lens microscope of the type he had described in Micrographia in 1665, the same design that Leeuwenhoek used, and using the glass pipe to effectively double the magnification, this lens apparently did not have the resolution nor did the room provide the visibility. "There was no discovery made."

It was therefore ordered, that against the next meeting pepper-water should be provided, and some better microscope than that made use of, that the truth of Mr. LEEWENHOECK'S assertions might, if possible, be experimentally examined.

Second try: "nothing could be seen"

A week later, at the meeting of November 8, 1677, Hooke had a new, improved experiment:

The first thing exhibited was the experiment charged on Mr. HOOKE at the last meeting, of examining pepper-water with better microscopes and thinner and small pipes. The fabric of the microscope for holding such pipes was new and more convenient and expeditious for such examinations than the usual forms, consisting wholly of pieces, which slid any ways very easily, and would stand fixed and steady in any posture, and admit light to the object every way:

by the comparing of which various ways of inlightening the object one might the more easily and certainly discern the true shape and constitution of any body.

The lens, the positioning, the lighting, it was all improved.

But notwithstanding the pepper-mixture was very strong, being made of rainwater and whole black pepper steeped in it for two or three days; and notwithstanding the microscope was much better than that shown at the last meeting; yet nothing of Mr. Leeuwenhoek's animals could be seen.

As it turned out, Hooke was getting interested in microscopy again.

Mr. HOOKE suggested same farther improvement of that instrument by making use of the convexity of the surface of the liquor itself (put upon the plates of Muscovy glass) for augmenting the body within the liquor; as also for augmenting the body beyond it.

Over the next six months, Hooke would continue his investigations, including letters from and a detailed response to Leeuwenhoek, in Microscopium, the second part of his book Lectures and Collections (title page left), published in 1678. Leeuwenhoek's contribution was titled "Two Letters concerning some late Microscopical Discoveries". Hooke's response was titled "The Author's Discourse and Description of Microscopes, improved for discerning the nature and texture of Bodies".

Third try: "there could be no fallacy"

At the next meeting a week later, Hooke was back for another try. On November 15, 1677:

The first experiment there exhibited was the pepper-water, which had been made with rain-water and a small quantity of common black pepper put whole into it about nine or ten days before. In this Mr. HOOKE had all the week discovered great numbers of exceedingly small animals swimming to and fro.

This time, he let the pepper steep longer and he had successfully seen the little animals before the meeting.

They appeared of the bigness of a mite through a glass, that magnified about an hundred thousand times in bulk; and consequently it was judged, that they were near an hundred thousand times less than a mite. Their shape was to appearance like a very small clear bubble of an oval or egg form; and the biggest end of this egg-like bubble moved foremost.

A hundred thousand was more a sense of an order of magnitude than an actual measurement, but Leeuwenhoek's claims were now credible.

They were observed to have all manner of motions to and fro in the water; and by all, who saw them, they were verily believed to be animals; and that there could be no fallacy in the appearance.

In an interesting choice of words, they were "believed" AND their appearance was "no fallacy". The whole process had led to this moment of replication.

They were seen by Mr. HENSHAW, Sir CHRISTOPHER WREN, Sir JOHN HOSKYNS, Sir JONAS MOORE, Dr. MAPLETOFT, Mr. HILL, Dr. CROUNE, Dr. GREW, Mr. AUBREY, and divers others; so that there was no longer any doubt of Mr. LEEWENHOECK'S discovery.

These men (see details on right) would not take Leeuwenhoek's word for it. They would not take the word of Leeuwenhoek's credible witnesses. They had to see for themselves. Birch concludes by noting what many useful experiments do; they suggest new experiments.

Notice was ordered to be taken of this discovery, and further trial was desired to be made upon rain-water alone; and upon rain-water, in which had been steeped, wheat, barley, and other seeds and grains: as also that blood and several other liquors should be after the same manner examined.

Manipulate the variables. Try rainwater alone; try other infusions. In addition to water, try blood. Over the next six months, Hooke would do all that and more, as he discussed in detail in Microscopium.

Science was new, but it was alive and well and in good hands with Robert Hooke and the philosophers of the Royal Society.



In Microscopium, (pp. 82-84) written shortly after, Hooke described and reflected on his attempts.

Upon the perusal of this Letter, being extremely desirous to examine this matter farther, and to be ascertained by ocular inspection as well as from testimonials. I put in order such remainders as I had of my former Microscopes (having by reason of a weakness in my sight omitted the use of them for many years) and steeped some black pepper in River water, but examining that water about two or three days after, I could not by any means discover any of those little creatures mentioned in the aforesaid Letter: though I had made use of small glass canes drawn hollow for that purpose, and of a Microscope that I was certain would discover things much smaller than such as the aforesaid Mr. Leeuwenhoeck had affirmed these creatures to be; but whether it were that the light was not convenient (the reason of which I shall shew by and by) having looked only against the clear sky, or that they were not yet generated, which I rather suppose, I could not discover any.

I concluded therefore either that my Microscope was not so good as that he made use of, or that the time of the [Page 83] year (which was in November) was not so fit for such generations, or else that there might be somewhat ascribed to the difference of places; as that Holland might be more proper for the production of such little creatures than England.

I omitted therefore farther to look after them, for about five or six days, when finding it a warm day, I examined again the said water; and then much to wonder I discovered vast multitudes of those exceeding small creatures, which Mr. Leeuwenhoeck had described; and upon making use of other lights and glasses, as I shall by and by shew, I not only magnified those I had thus discovered to a very great bigness, but I discovered many other sorts very much smaller than those I first saw, and some of these so exceeding small, that millions of millions might be contained in one drop of water. I was very much surprized at this so wonderful a spectacle, having never seen any living creature comparable to these for smallness: nor could I indeed imagine that nature had afforded instances of so exceedingly minute animal productions. But nature is not to be limited by our narrow appre­hensions; future improvements of glasses may yet further enlighten our understanding, and ocular inspection may demonstrate that which as yet we may think too extravagant either to feign or suppose.

Of this, A later Discovery of Mr. Leeuwenhoeck does seem to give good probabilities; for by a Letter of his since sent (the which is hereunto annexed) it appears he hath discovered a certain sort of Eels in Pepper-water, which are not in breadth above one thousandth part of the breadth of a hair; and not above a hundredth part of the length of a vinegar Eel.