Fleas, mould and plant cells: under a 17th century microscope with Robert Hooke
This week we celebrate the 379th birthday of Robert Hooke, a Fellow of the Royal Society and key figure of early modern natural history and natural philosophy, born on 28 July 1635. Many of Hooke's innovations paved the way for a more rigorous scientific analysis of materials, for which we in Collection Care are very grateful. To mark the occasion we are thrilled to host a guest post from Puck Fletcher who has just completed a doctorate on space, spatiality, and epistemology in Hooke, Boyle, Newton, and Milton at the University of Sussex:
Hooke’s most famous work is the Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries thereupon, published in 1665 by the Royal Society. It is a descriptive work detailing sixty observations of specimens at magnification, starting with the point of a needle, ranging through silk, glass drops, hair, and various plants, seeds, and tiny insects, all viewed through a microscope. It closes with observations of the fixed stars and the moon as seen through a telescope.
Two cross sections of cork and a ‘sensible’ plant. In his description of cork, Hooke coined the term ‘cell’ for biological contexts. Image source.
The project was a collaborative one started by Christopher Wren who, in 1661, so impressed Charles II with his drawings of magnified fleas and lice (possibly the ones on which the corresponding Micrographia engravings were based), that the King requested more. Wren persuaded Hooke to undertake the bulk of this work and over the next few years, Hooke amassed his collection of observations, regularly bringing new drawings to the meetings of the Royal Society for approval by the other members.
Among the drawings and observations in Micrographia is this famous and extraordinarily detailed large-scale illustration of a flea. BL Shelfmark: 435.e.19, XXXIV. Image copyright The British Library Board. Read more.
The impressive folio volume contains thirty-eight highly detailed engravings, which turned the book into an instant bestseller and secured its reputation as the most beautiful and lavish work of early European microscopy. The sense of magnified scale is staggering. A head or body louse, for example, is just a few millimetres long, but the engraved image is 52 cm long, roughly two hundred times actual size, a level of exaggeration that is emphasized by the fact that, large as the volume is, the reader must still unfold the oversized plate to view it.
Engraved image of a head or body louse, roughly two hundred times actual size. Image source.
For his readers, Hooke’s illustrations brought a whole new world into view. Hooke captures this excitement in his preface, describing how, by means of instruments like the microscope, ‘the Earth it self, which lyes so neer us, under our feet, shews quite a new thing to us, and in every little particle of its matter; we now behold almost as great a variety of Creatures, as we were able before to reckon up in the whole Universe it self.’ Pepys was famously so enamoured of the book that the day after he brought home his copy, he stayed up until two in the morning reading it, describing Micrographia in his diary as, ‘the most ingenious book that I ever read in my life’.
When looking at the large-scale, clear engravings in Micrographia, it is easy to imagine that this was the view Hooke had in his lens and that his task was simply that of looking and then recording what he saw. However, the practice was much more difficult and required considerable skill and experience – when Pepys looked through his microscope, he was disappointed to find that at first he couldn’t see anything at all! The lens making technology of the time meant that impediments to clear vision such as chromatic aberration or artefacts in the glass were not uncommon, and the view through a microscope was often blurred, distorted, and dark. It was difficult to make out true colours or to tell whether a shadow was a depression or protuberance, and the field of vision was quite small.1
Part of Hooke’s contribution in Micrographia was his skill as an instrument maker and technician. Although, as he reports, he had difficulties in seeing through his microscope, Hooke made his own adaptations to the commercially manufactured instrument, in particular devising an improved light source, which he called his ‘scotoscope’.
The microscope, featuring an improved light source. Image source.
Hooke also worked diligently and looked very carefully, making multiple observations from multiple angles, of multiple specimens, created with various preparation techniques, to gather enough visual information to be able to produce a single image of what the whole object looked like, as near as he could make out. For Hooke, the act of looking through the microscope and recording what he saw was an interpretive one.
Hooke’s observations have been praised by modern scientists for their accuracy, and Howard Gest even credits him with the first accurate description and depiction of a microorganism, the microfungus Mucor, described by Hooke as ‘blue mould’.2
The microfungus Mucor (‘blue mould’). Image source.
In his preface to Micrographia, Hooke heralds ‘artificial Instruments’ such as the microscope and telescope, and the methods of the new science based on observation and the careful and rational scrutiny of results, as at least partial correctives for the failings of fallen man and his limited sensory faculties. He also looks forward to the technology of the future, which he believes will enable man to see even more clearly.
‘’Tis not unlikely, but that there may be yet invented several other helps for the eye, at much exceeding those already found, as those do the bare eye, such as by which we may perhaps be able to discover living Creatures in the Moon, or other Planets, the figures of the compounding Particles of matter, and the particular Schematisms and Textures of Bodies.’
1Brian Ford’s wonderful book, Images of Science: A History of Scientific Illustration (The British Library, 1992), pp. 182–83, contains a photograph of the partial and distorted view through the sort of lens used by Hooke.
2Gest, Howard, ‘The Remarkable Vision of Robert Hooke (1635–1703): First Observer of the Microbial World, Perspectives in Biology and Medicine, 48.2 (2005), 266–72 (p. 267).