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167619.  Thu Apr 19, 2007 4:40 am Reply with quote

Flash wrote:
Perhaps, but my point is that it is also fairly easy to be funny about.

True enough. I'm a scientist, not a comedian :)

Molly Cule wrote:
Cavendish worked this out at home, using a machine he made himself out of weights, pendulums and wires. At the heart of the machine were two 350-pound lead balls.

"The idea was to measure the gravitational deflection of the smaller spheres by the larger ones, which would allow the first measurement of the elusive force known as the gravitational constant

Oh god! I've done that one as well. Very hard to do, and fantastically sensitive equipment. Not really ideal conditions to try doing it in a crowded physics lab with heavy footed undergrads stomping past every few minutes.

I imagine Cavendish was able to generate more favourable conditions.

167641.  Thu Apr 19, 2007 5:32 am Reply with quote

I have a picture of the apparatus he used which shows him standing outside a sealed room looking through a spyglass built into the wall.

The science involved is just complex enough to be impossible for us to convey meaningfully without Stephen being interrupted. If we use the question at all, it's probably best viewed as a way of getting to the subject of the eccentricity of Cavendish himself.

167642.  Thu Apr 19, 2007 5:36 am Reply with quote

What, the experiment to measure the gravitational deflection of two small balls suspended on a thread by two larger balls placed nearby? Is that really complex?

167650.  Thu Apr 19, 2007 5:44 am Reply with quote

OK, here's what would happen:

Stephen: So what this man Cavendish wanted to do, this was in 1798, was to measure the density of the Earth as a whole. So he made this apparatus with two big lead balls and two little ones at either end of two arms and ...

Alan: He had balls on his arms?

167669.  Thu Apr 19, 2007 6:00 am Reply with quote

Ah, I see. I was forgetting the Alan Effect :)

Although is there not some comedy mileage about explaining how Cavendish managed to measure the mass of the Earth by using his impressively large balls?

167673.  Thu Apr 19, 2007 6:02 am Reply with quote

Makes me laugh.

Molly Cule
167684.  Thu Apr 19, 2007 6:08 am Reply with quote

Can I see the photo? Do you have it on a computer?

167692.  Thu Apr 19, 2007 6:15 am Reply with quote

Here's a nice description with some diagrams (but no photos).

167700.  Thu Apr 19, 2007 6:19 am Reply with quote

Is this it?

167707.  Thu Apr 19, 2007 6:26 am Reply with quote

That's the one. I'm not saying that we shouldn't run this, just that it will not in practice be possible for Stephen to give a coherent explanation of the science involved without being interrupted. However, he might well be able to run Dr Bob's impressive balls joke and then segue into the stuff about Cavendish's transvestism etc. And of course we'd give him a note about suspending plumblines on either side of a mountain, etc, so that he at least has the science to hand.

167713.  Thu Apr 19, 2007 6:42 am Reply with quote

How about this:

To find out just how strongly masses attract each other, Cavendish suspended a rod with small spheres at either end close to another rod with two huge spheres at either end. Over time, he measured how much the small spheres were swinging towards the larger ones, and, knowing the masses involved, calculated gravity's 'power'.

We could easily show a diagram of the setup, and who cares if there are 'ball' gags. Maybe Stephen could start of with a formal 'huge balls gag embargo'...

167714.  Thu Apr 19, 2007 6:43 am Reply with quote

Where did the image above come from please?

167716.  Thu Apr 19, 2007 6:45 am Reply with quote

Sorry lizzie, I found it when repeatedly hitting the random article button on wikipedia.

Here is a link.

167718.  Thu Apr 19, 2007 6:48 am Reply with quote

The image properties show it to be from Wikipedia ( The Wiki lists it as Public Domain on the grounds that Cavendish died so long ago, which is nonsense, of course.

The book I saw it in is the Children's Encyclopedia, published some time in the 1920s. It gives no credit for the picture, so perhaps it was originally drawn for that publication?

167742.  Thu Apr 19, 2007 7:15 am Reply with quote

I'll investigate. Despite it being out of copywrite, of course that doesn't mean it doesn't have to be cleared. I'll look into it - thanks for the link!


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