Thomson served as professor of natural philosophy (1846-99) at the University of Glasgow. One of his first projects was to calculate the age of the Earth, based on the rate of cooling of the planet--assuming it had once been a piece of the Sun. (His result--20 to 400 million years--was far short of the current estimate of 4.5 billion years.) Greatly interested in the improvement of physical instrumentation, he designed and implemented many new devices, including the mirror-galvanometer that was used in the first successful sustained telegraph transmissions in transatlantic submarine cable. Thomson's participation in the telegraph cable project formed the basis of a large personal fortune.