Classic kit: McLeod's vacuum gauge
© THE ROYAL SOCIETY
While the heat was mostly focused on biology, physical scientists were not immune to the debate's impact. Among the most prominent was a chemist, Herbert McLeod, who felt it necessary to declare his position and gathered others to join him.
By the time it failed in 1856, McLeod had moved on to the more prestigious Royal College of Chemistry (RCC) in Oxford Street, under August Hofmann (See Chemistry World, January 2010, p68). It must have been an exciting time - the group, wrestling with coal tar, attracted many of the best young chemists. It is an indication of his talent that McLeod quickly became favourite assistant to the famously clumsy Hofmann. Two years later, when Hofmann moved back to Germany, McLeod followed him. But when Hofmann moved again in 1864 - from Bonn to Berlin - McLeod returned to London.
He found a post with Hofmann's successor at the RCC, Edward Frankland. What is not clear is what he actually did. There are no publications to draw on, though his contemporaries report that he had worked on dye synthesis. But organic chemistry was clearly not his thing, and back in London he became interested in the latest developments in the handling of gases. August Töpler (See Chemistry World, January 2011, p68) unveiled his piston pump in 1862. McLeod's contemporary at the RCC, Hermann Sprengel (See Chemistry World, February 2008, p67) invented his much faster mercury dropping pump in 1865. So the study of gases at low pressure could now become an almost mainstream occupation.
The real problem was how to measure the extraordinarily low pressures that these pumps reached. Even with the best cathetometer - a travelling microscope fitted to a scaled track - a standard manometer lacked the precision required.
Compact vacustat McLeod gauges are often preferred in modern labs over electronic equivalents
But McLeod was also a devout Anglican, and in the febrile atmosphere of the early 1860's, he and a group of colleagues wrote a declaration expressing their objection to how 'researches into scientific truth are perverted by some in our own times into occasion for casting doubt upon the truth and authenticity of the Holy Scriptures'. Circulated as a petition in 1864, the declaration gathered a substantial number of adherents - many of them chemists from the Royal College - and created quite a stir. But it was a flash in the pan and the campaign fizzled, and today McLeod is remembered as much for his Catalogue of the scientific papers of the Royal Society as he is for his gauge.
But the argument between science and religion continues, and has become ever more political. Ironically, the religious literalists, particularly those in the US, argue that science itself is a belief system much like a religion. What, one wonders, would McLeod have made of that?
Andrea Sella teaches chemistry at University College London, UK
H McLeod, Philos. Mag., 1874, 48, 110
McLeod's Catalogue of the scientific papers of the Royal Society 1800-1900 can be found online at the related link below
McLeod's Catalogue of the scientific papers of the Royal Society 1800-1900
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