There's a permanent display in London Science Museum of King George III's collection of scientific instruments in 18th century. Consider Boyle-Hooke Vacuum pump made in 1659.
It is very hard and takes enormous effort to pump air out of the glass container. They sometimes used horses to pump air out. So, the question is: Why is it so hard to create a vacuum by pumping air out of the glass container? Where does the opposing force the prevents air from being removed come from?
Pictures of a Klein bottle, a pegasus computer and Babbage's Difference Engine here.
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In the previous post on this topic, I discussed the various types of noisy vacuum pumps, both clean and dirty varieties.
A great many physics experiments need to be conducted at low pressures, in order to avoid sample contamination, thermal effects, or dissipative forces produced by interaction with air.
I spent most of Saturday in the lab, swapping out a turbopump that was starting to die. How could I tell? Well, for one thing, it made an awful noise, even more than usual for a noisy pump.
Hat-tip to a reader for bringing this to my attention.
Should a breast-feeing woman be allowed extra long breaks during her nine-hour medical licensing exam?
> Q: Where does the opposing force the prevents air from being removed come from?
A: The very large, and quite heavy column of air above our heads -- 15lbs/sq.inch or so. We live at the bottom of an ocean of air.
The force the horses push against is the weight of the atmosphere itself. In effect, they are lifting a column of air the height of our atmosphere.