One of the episodes in the history of flight involves two aeronef designs that trace their inspiration to an experiment that may or may not have contributed a bit to the development of the ideal gas laws by Boyle and Hooke, which themselves led to the development of the first steam engine. In effect, the little episode , fruitless in the history of the development of flight, shows links with other episodes in the history of science and technology.
The designs in question concern first a 1709 airship proposal by a portuguese scientist named de Gusmao whose designs for aero lift involved the exploitation of lighter than air volumes that would carry the ship up. He was renouned for making a model balloon fly up to the roof. His airship design involved an apparatus or grid to to heat the air underneath a canopy that covered the airship, a conceptual predecessor of the hot air balloons. He was encouraged in his design efforts by another lighter-than-air idea, 37 years older at his time, and unfortunately impractical , by a Fransisco di Terzi, who imagined an airship relying for its buoyance on thin copper vacuum spheres .
Terzi's idea of the vacuum spheres , and the calculation of the relative weights of the air-less copper spheres and their equivalent in air, was in fact, despite the oversight quite brilliant and sensical. Yet it derives from another vacuum sphere , one that was developed twenty years earlier.
That sphere, as it turns out, was a much more famous sphere, that in fact was not a sphere but consisted of two hemispheres named after the town where they were conceived , Magdeburg.
The two hemispheres of copper , about a foot in diameter, were made in 1650 and demonstrated repeatedly at royal courts through the following dozen years by the german scientist and public servant, Otto von Guericke who set out to demonstrate the power of the pressure of gazes like the air and fluids like the atmosphere. In so doing, he wanted to disprove a long held notion , originating with Aristotle, on the reason why solids were held together so tightly , what made substance, utterly divisible into dust particles, be able to hold itself.
Artistotle's proposition stipulated that nature abhors a vacuum, and in the same way , earth is attracted downward and fire is attracted upward, there was a natural disposition to fill in in gaps in space causing matter to condensed in its solid forms. This interpretation of his thus came to be known , by Guericke's time as "horror vacui".
Guericke seemed to believe that it was rather the pressure of the air , a force of our atmosphere that held solids together. An erroneous notion that can be more than forgiven for the ingenuity with which he set out to prove it.
The hemispheres were to be brought and held firmly together after covering their rims with a layer of grease or naphta oil. They were then to be emptied of their air content by means of an air pump von Guericke had developed specifically for the experiment. Once devoid of air, the hemispheres became so tightly held together that no amount of available force could do the work of displacing them apart. To demonstrate this fact each hemisphere was tied to a team of horses , both facing opposite directions. Both teams would then be made to pull the hemispheres in opposite directions, but no matter how hard the horses pulled the hemispheres held tightly. the enormous force of atmosphere pressure on the vacuum inside the sphere held its hemispheres together.
In setting up this experiment Guericke demonstrates some fine details.
- The experiment was a success and was even popular , making it part of popular knowledge not just insular recondite science.
- The experiment's apparatus was the world's first artificially (human) made vacuum enclosure. This particular activity, creating a vacuum , is very important to the advancement of modern chemistry, and later electronics.
- The design of the air pump to create the vacuum went on to contribute to Robert Hooke and Robert Boyle's work and consequently to the prolegomena of modern chemistry and thermodynamics that they both have laid down. Other chemistry researchers followed Boyle and Hooke's example and made use of Guericke's pumps to enable to examine chemical propertie and reactions in a vacuum, greatly aiding the advancement of chemical science. Vacuum flasks and tubes later carried electrical research through the invention of incandescent and fluorescent light , the radiotelegraph and the radio , and the vacuum tubes of the television and the computer.
The graph below happens to capture some of the threads of this short historical episode,
but moreover it looks like a useful tool for rendering (and variously compressing, analyzing visualizing and summmarizing text such as those from which the information in this note was gathered.
The texts used were largely en.wikipedia articles, plus the illustr. ...
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