+----------------------------------------------------------------------+ | [Illustration: Watch-case (_circa_ 1600).] | +----------------------------------------------------------------------+ Such was the state of clockwork when Galileo, the great astronomer, then a medical student at Pisa, happened to discover, while gazing up at the roof of the cathedral when he should, perhaps, have been devotionally occupied, that the lamps suspended therefrom by chains of equal lengths, swung, and made their vibrations in long or short arcs, in almost the same space of time,--a fact, the truth of which he ascertained by the beats of his pulse. +----------------------------------------------------------------------+ | [Illustration: Table-Watch, _circa_ 1630.] | +----------------------------------------------------------------------+ This isochronal property, as it was called, was described in a treatise which he published at Paris in 1639, entitled 'L'Usage du Cadron ou de l'Horloge physique universelle.' The first application which Galileo made of his discovery was the professional one of testing the rate and variations of the pulse, and it is even denied that he did more than suggest its applicability to clockwork. +----------------------------------------------------------------------+ | [Illustration: Ancient Silver Dial and Gold-cased Watch. One hand.] | +----------------------------------------------------------------------+