In the latest Age of Invention newsletter, Anton Howes relates how a mistaken belief still led to a significant improvement in health:

The west view of Newgate Prison, circa 1810, by George Shepherd (1784-1862).
Wikimedia Commons.

One of the most worrying diseases of the mid-eighteenth century was typhus. We now know that it is spread by lice or fleas, but at the time, like so many other diseases, it was thought to be caused by noxious air — “malaria”, for example, literally means “bad air”. This was not a silly theory. It was based on empirical observation, which perhaps explains why the belief in such noxious miasmas persisted for so long — well into the late nineteenth century, if not the early twentieth, before finally being ousted by germ theory. Our ancestors were not stupid, no matter how strange their beliefs might appear in hindsight. (Also take alchemy, or the belief that some animals spontaneously generated.)

The Central Tower of the Palace of Westminster is actually a disguised ventilator.
Photo by Cary Bass via Wikimedia Commons.

Typhus fit the miasma theory especially well because it frequently appeared in confined spaces, like ships’ holds, prisons, mines, workhouses, and hospitals. The disease was thus often called “gaol fever”, or “hospital fever”. And there was the fact that at least one of the solutions designed to combat miasmas, the ventilator, actually seemed to work. This ventilator was not the kind that is in such high demand right now, used to help feed oxygen into patients’ lungs, but instead a machine used to get the air flowing in and out of confined spaces — like a 1740s air-conditioning unit.

At first glance, removing the stale air from a space shouldn’t do anything against typhus. But mortality declined drastically in the prisons and ships to which the ventilator was introduced. It halved the number of deaths per year in Newgate prison, where the bellows-like machinery was powered by a windmill, and the inmates of the Savoy prison fared even better. On ships, too, mortality declined among mariners, passengers, soldiers, and especially among the group that suffered most from long voyages across the eighteenth-century Atlantic: slaves.

But it’s not clear exactly why. After all, the ventilator did not kill the typhus-ridden lice or fleas. I have a few theories as to what must have been going on. Perhaps, by improving the supply of oxygen to confined spaces, people’s bodies were simply better served to deal with all manner of diseases. Surgeons aboard slave ships sometimes noted that, without proper ventilation, many slaves would simply die in the night of suffocation. Or perhaps the ventilator’s effectiveness had something to do with its drying effect. The machine was used to prevent grain stores from becoming humid, thus staving off damp-loving weevils. The ventilators might thus have staved off typhus through a similar means: although I’m not so certain about body lice, humid conditions are preferred by fleas. Regardless of the real reasons, the ventilators worked, and even when they did not reduce mortality, they made confined spaces more bearable for those who had to endure them. Ship captains reported that they did not even have to force their sailors to pump the ventilator’s bellows, because they liked the cool air so much. Ventilators were soon installed in the House of Commons, and in many of London’s theatres.

From the Wikipedia entry on architectural ventilation:

The development of forced ventilation was spurred by the common belief in the late 18th and early 19th century in the miasma theory of disease, where stagnant ‘airs’ were thought to spread illness. An early method of ventilation was the use of a ventilating fire near an air vent which would forcibly cause the air in the building to circulate. English engineer John Theophilus Desaguliers provided an early example of this, when he installed ventilating fires in the air tubes on the roof of the House of Commons. Starting with the Covent Garden Theatre, gas burning chandeliers on the ceiling were often specially designed to perform a ventilating role.

Mechanical systems
A more sophisticated system involving the use of mechanical equipment to circulate the air was developed in the mid 19th century. A basic system of bellows was put in place to ventilate Newgate Prison and outlying buildings, by the engineer Stephen Hales in the mid-1700s. The problem with these early devices was that they required constant human labour to operate. David Boswell Reid was called to testify before a Parliamentary committee on proposed architectural designs for the new House of Commons, after the old one burned down in a fire in 1834. In January 1840 Reid was appointed by the committee for the House of Lords dealing with the construction of the replacement for the Houses of Parliament. The post was in the capacity of ventilation engineer, in effect; and with its creation there began a long series of quarrels between Reid and Charles Barry, the architect.

Reid advocated the installation of a very advanced ventilation system in the new House. His design had air being drawn into an underground chamber, where it would undergo either heating or cooling. It would then ascend into the chamber through thousands of small holes drilled into the floor, and would be extracted through the ceiling by a special ventilation fire within a great stack.

Reid’s reputation was made by his work in Westminster.