Page:Biographies of Scientific Men.djvu/69

Rh

Among Cavendish's other investigations may be mentioned his work on the thermometer and temperatures; he proved that heat was a mode of motion, thereby refuting the material theory. The origin of the "fur" in a tea-kettle was first noted by Cavendish, and the fact that hard waters could be rendered soft by the addition of lime was demonstrated by him. He also proved, by quantitative experiments, that fixed air (carbon dioxide) was heavier than common air, and performed other work on gases. He invented the eudiometer; but his two crowning discoveries were the determination of the composition of water, and the weight of the earth.

Although Cavendish retained the terminology of the phlogistic doctrine, he practically admitted the essential point of the nouvelle chimie of Lavoisier, namely, that calces are compounds of metals and dephlogisticated air (oxygen). He was elected an F.R.S. in 1764, and in 1801 one of the eight foreign associates of the French Académie des Sciences.

Of posthumous honours, the seventh Duke of Devonshire, himself a distinguished mathematician, erected and