History of Bacteriology :The Rebirth of Microscopy

It was Robert Hooke who first popularised microscopy when he published his seminal work in "Micrographia". He had produced exquisite images of the eye of a fly, of tiny fleas, and of the tiny structures within a cork plant, naming them "cells". However, within five years of its publication, many of its findings were overshadowed by the work of a  mysterious Dutchman.

 The Dutchman in question was a successful garment seller who had developed a keen interest in Microscopy. In his workshop he had quietly begun to develop some of the most advanced microscopes of his era. This man was Anton Leeuwenhoek, and is often credited as the "Father of Microbiology". 

He created the first microscope powerful enough to see the Microbes. He could see organisms too small to be visible to the naked eye, and stunned the world with his intricate drawings of these tiny creatures. He was the first person to discover the existence of single celled organisms, and his regard spread throughout Europe.
 Robert Hooke became a massive fan of Leeuwenhoek, and a supporter of his work. He had but one problem. The entire field of microscopy was "Reduced to a single Votary, which is Mr Leeuwenhoek". Whilst the world was filling with astronomers, mathematicians and naturalists, there was only one person who was looking into the tiny world of single celled organisms.

Why was Anton van Leeuwenhoek the only microscopist left in the world ?   

Hooke believed that it was the lack "of the inquisitive genius of the present age". i.e. no-one was interested in the subject.  But there were somewhat justifiable reasons why people weren't interested in microscopy.

 Leeuwenhoek was intensely defensive of his discoveries, fearing that some other may come along to take the credit. It was an understandable fear. Quite notably Robert Hooke had a long standing dispute with Newton over who discovered gravity first, and believed that Newton had purloined his ideas on the inverse square law and gravitational attraction*.

This is why Leeuwenhoek kept his methods secret, apprenticed no students, and refused to show anyone the microscopes he had used to make his discoveries. Leeuwenhoek's place in history was secured, but his legacy was not. 

When Leeuwenhoek died, he took microbiology with him. Whilst microscopes could be found in some places, they were merely curiosities with no practical function for those wanting to push the boundaries of science. They were incredibly difficult to use, and often produced distorted images, due in part to chromatic aberration. No-one knew how Leeuwenhoek got around these problems, and it would be a long time before anyone would create microscopes of comparable power.

Solving Chromatic Aberration
Lenses work by re-directing light into a focal point by taking advantage of light slowing down when it enters glass. Using shaped glass allows you to bend light, and focus it to magnify an image.

Each part of the wavefront entering the lens is slowed down, but because of the shape of the lens, they are all slowed down for different lengths of time, causing them to be distorted. This means that wavefronts coming out of the convex glass end up focused on one point.

This effect is the basis for telescopes, spectacles and your eye's ability to read the words I've just typed.

Here is the problem. Any optical material can split different wavelengths of light. This is what happens when we pass light through a prism, or when it goes through the raindrops to form a rainbow. The different wavelengths of light are slowed down to different speeds, which is what causes them to separate.
This effect is what causes chromatic aberration. 

Chromatic aberration causes multiple images of different colours to have different focal points. This results in blurry and miscoloured images. Leeuwenhoek's microscopes had sidestepped these problems by being incredibly small, and didn't suffer from chromatic aberrations due to the incredibly small distances involved.

It was an amateur optician named Chester Moores Hall who eventually solved the problem. The answer came to him as a result of his studies of the human eye. He noticed that the human eye itself had a spherical lens, so why wasn't human sight blighted with chromatic aberrations ?

He hypothesised that the jelly like vitreous humour in the eye held the answer. Somehow, the vitreous humour cancelled out the aberrations caused by the lens. He decided to use a similar method to compensate for the chromatic aberrations. He knew that some glasses would separate light in the opposite way to others. So if he used a type of glass that would naturally bend light the opposite way to the lens, he could use it to cancel out the splitting of light caused by chromatic aberration. He decided to use flint glass to form a cover over the lens, and theoretically correct for any aberration.

He had one big problem. He didn't know how to grind his own lenses. He needed to get someone to make his special lenses, but he didn't want any of them to figure out that he had solved chromatic aberration.
To keep his discovery secret, he used different lens-makers to make each part of his new invention separately. One would make the objective lens, and the other would make the corrective cover for it.
But Chester Moores Hall fell victim to an unfortunate coincidence. Neither of these lens makers could make the parts he requested, and both of them decided to subcontract the work onto a man named George Bass. When he constructed both of the primary parts for the lenses, he literally put the pieces together, and figured out what Chester Moores Hall had done.

George Bass mentioned this discovery to another optician, John Dollond, who had also been struggling with the same problem. Dollond immediately patented this discovery, and started selling corrective lenses that accounted for chromatic aberration.

It was his son, Peter Dollond,  who decided to fully enforce those patents. By this time, many other opticians around London were using chromatically corrected lens. Peter Dollond managed to use his fathers patent to try to run them out of business. In the subsequent legal proceedings, Dollond's competitors believed they had an ace in the hole. They called Chester Moores Hall to the stand, who confirmed that he was indeed the true inventor of the achromatic lens, giving them the right to dispute the patent.

The problem was that Chester Moores Hall kept it to himself, which became a major sticking point for the judge. The Judge ruled in favour of Dollond, because Dollond had tried to make a profit from his invention.

 It was a Dutch instrument maker named  Jan van Deijl who had managed apply achromatic lenses to microscopes. But he wanted to get them absolutely right, and spent such a long time perfecting them that the work had to be passed down to his son Harmanus, who would eventually publish that work and set up a company to start selling microscopes.  They suddenly became popular again, and scientists like Giovanni Amici and Joseph Jackson Lister* made further improvements to this design. Microscopy had been successfully rescuscitated.

Soon these instruments were in high demand, with microscope manufacturers popping up across Europe, and then across America.  They became the essential tools for naturalists and physicians, and microscopy became the forefront of important research during this era.

During the next month I will be writing a series of posts on the history of microbiology, focussing mostly on the massive leaps that happened during the 19th century. If I was to point at one reason why microbiology would finally came into its own during this era, I would point you to the microscope. Many of the greatest discoveries of this era simply would not have happened if these instruments had not become fixtures on the desks of reputable scientists around the world, waiting to be used.

References and Further Reading

Cassedy J.H. (1976). The Microscope in American Medical Science, 1840-1860, Isis, 67 (1) 76. DOI: 10.1086/351546

Dobell, Clifford (1932). Antony van Leeuwenhoek and His "Little Animals": being some account of the father of protozoology and bacteriology and his multifarious discoveries in these d

isciplines. New York: Harcourt, Brace and Company. 

Department of the History of Science (Harvard)  Description of Harmanus Van Deijl's compound microscope

Nineteenth-century Scientific Instruments by Gerard L'Estrange Turner

Peter Dollonds answers Jesse Ramsden -http://www.mhs.ox.ac.uk/sphaera/index.htm?issue8/articl5

* The impression I get from what I've read is that Robert Hooke, like many scientists of his era had come up with the rough idea that celestial bodies attract eachother, and that attraction dissipates with distance, but it was Newton who actually went ahead and created a mathematical model with a series of quantifiable laws to explain these phenomena. Hooke had the rough idea of what was going on, Newton had the detailed explanation.

** Not to be confused with his son, Joseph Lister, the pioneer of antisepsis.