Demonstrating How Sound Can’t Travel Through a Vacuum – Christmas Lectures with Charles Taylor

Demonstrating How Sound Can’t Travel Through a Vacuum – Christmas Lectures with Charles Taylor


Now I’m going to do a lot of different kinds
of experiments and one of them is typified by this piece
of apparatus here. This is what one might call an old faithful. The experiment that I’m going to do with this was first done in 1705. So it’s a very old
one. It was done by a man called Francis Hawksby who quite a lot of people think was the first, and one of the great, lecture demonstrators. And he did the experiment before the Royal
Society. We have a clockwork mechanism that we’ll ring
the bell, but we’ve pumped out all the air from this
bell jar and so when I start it running, you won’t
be able to hear it. You can see the hammer hitting the bell. It’s got a life of its own, this plunger, I’ve got to hold onto it. But you can see it striking the bell but because there’s no air inside, you can’t
hear it. Now I’m going to let the air in. And as we let the air in… Now I think you can hear the bell. Quite clearly. And that’s a very nice experiment to demonstrate how air is needed for the transmission of
sound. Now this experiment was done a good deal later in the middle of the 19th century by John
Tyndall who in fact followed Michael Faraday as director
of this institution. And here we have a picture in Faraday’s book of this apparatus. I think you can see, although the bell jar
may be different, the actual clockwork is very much the same as the clockwork that we have in the bell
jar there. And I think the fact that the hammer, this
hammer here, is so similar to the hammer on that clockwork, more or less proves that that is the original.

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