FAHRENHEIT, GABRIEL DANIEL, well known for the modifications which he introduced in the construction of the thermometer and barometer, was born at Dantzic about the end of the seventeenth century. After engaging for some time in commerce, his inclination for natural philosophy induced him to relinquish business; and having travelled through Germany and England to enlarge his knowledge, he settled in Holland, where the most celebrated men in this branch of science—s'Gravesande and others—were his teachers and friends. In 1720 he first conceived the idea of substituting mercury for spirits of wine in the construction of thermometers—an improvement which greatly enhanced the accuracy of the instrument. He took as the limit of greatest cold that which he had observed at Dantzic during the winter of 1709, and which he could always produce artificially by a mixture of equal quantities of snow and sal-ammoniac. The space between the point to which the mercury fell at this temperature and that to which it rose in boiling water, he divided into 212 parts; and this distinguishes his thermometric scale from that of Réaumur.
During his residence in Holland, Fahrenheit employed himself in constructing a machine for draining the parts of the country exposed to inundations; for which he obtained a patent; but its full development was interrupted by the death of the inventor, which took place in 1740. The changes which s'Gravesande introduced (whom he had requested to complete the machine for the benefit of his heirs), rendered it so useless in the first trial that no further attempt was made to complete it. (See THERMOMETER, and METEOROLOGY.)