Henry Cavendish: the man and the measurement

Cavendish's experiment to find the mean density of the earth was his last published experiment and the one which, ultimately, has proved the most significant. In a career spanning many scientific topics, this is the one which has gone down in history as 'The Cavendish Experiment'. Henry Cavendish was the grandson of the Second Duke of Devonshire and son of Lord Charles Cavendish. Reclusiveness ran in the family, and Henry Cavendish retired into a private world of science. It is entirely consistent with his personal characteristics that he removed the measurement of the density of the earth from the realm of field investigations to the privacy of his own laboratory, extrapolating his results theoretically to the wider world.

Cavendish's concern with the mean density of the earth began with criticisms of astronomical investigations which ignored the attraction of mountains: his main interest in the experiment was in the potential precision of the method and his paper reads rather like a dissertation on errors. He was an indicator of the emerging science of precision measurements that gained momentum during the following century. It is noticeable that Cavendish made no attempt to use his experiment to determine the gravitational constant. Indeed, this is a question that would have been difficult to ask within the science of the time. However, it is due as much to the subsequent importance of this fundamental force as to the precision of his work that Cavendish's experiment has outlived the problem of the density of the earth.