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.

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):

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 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.