One thing I did which I enjoyed which... which was the theory of using the earth as a detector of gravitational waves. That's another kind of astronomy, gravitational wave astronomy, so that was an original contribution which I'm rather proud of. I published a paper on seismology in The Astrophysical Journal which I think is a unique achievement. It's an interesting question: If you have a gravitational wave coming in from a distance, some astronomical source, with a very precise frequency, something like just a rotating dumbbell or something far away, a binary neutron star or something of that kind... can you see the earth resonating with seismographs? And the answer is, you can, but of course the coupling between the gravitational wave and earth is very, very small, and I worked it out. It was an interesting piece of theory, and you... you have the coupling between the gravitational wave and the earth going with the cube of the ratio of the sound velocity to the light velocity. Since the ratio is 10^-5, the coupling's strength is about 10^-15, so that's why it's such a weak signal. But in principle it could be observed and it's interesting that you could... it has a lot of rather interesting characteristic features: because the earth is rotating the lines, the frequencies, will actually be split into rotational components, and since the gravitational wave is a quadropole, you actually get a quintuplet of frequencies. So it has some amusing sort of quasi-quantum mechanical aspects, but needless to say, nothing of that kind has actually been observed. I think it's worth looking for and maybe one day it will be observed.