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38 solid body, he believed to be protected from the great heat of the elastic fluid of its own atmosphere by dense planetary clouds; it was diversified by mountains and valleys, and was in every way analagous to the Earth and the other planets. "We need not hesitate to admit," he said in 1794, "that the Sun is richly stored with inhabitants." In 1801, after further close study, he claimed that all his former arguments had been confirmed.

Herschel's theory met with general acceptance for many years. It harmonised with the trend of later eighteenth century thought, which—possibly as a result of the reaction from narrow theological views of the Earth's supreme place in nature—shrank from the idea of empty worlds. It was not until the invention of the spectroscope that the theory was universally abandoned. Untenable though it was, it was the first serious attempt to co-ordinate the isolated facts ascertained concerning phenomena of the solar disc.

The fallacious nature of his theory should not blind us to Herschel's great work as an observer of solar phenomena. In his paper of 1794 he noted the existence of "elevated bright places " which, after Hevelius, he named faculae. "I see these faculae extended . . . over about one-sixth part of the Sun. . . . Towards the north and south I see no faculae; there is all over the Sun a great unevenness in the surface, which has the appearance of a mixture of small points of an unequal light; but they are evidently an unevenness or roughness of high and low parts." Very few details of the solar surface escaped his persistent scrutiny. His paper of 1801 described the process of spot-formation with a wonderful accuracy of detail. Curiously enough, Herschel—although he devoted attention to the prevalence or absence of spots—failed to notice the sun-spot period. Probably he would have done so, had his attention to the Sun been more exclusive.

Herschel's solar work was not purely telescopic. His investigations on light and heat occupied a great deal of