monstrated by De la Hire in the crypt of the Paris observatory.
Christian Wolf, of Halle, and Olof Römer, of Copenhagen, both in 1709, are also named as the first to use mercury as a heat measuring liquid, but in spite of these many claimants the fact remains that Fahrenheit, in 1714, was incontestably the first to construct mercury thermometers having reliable scales. But this anticipates.
The need of a standard scale, easily made and based on constant phenomena that can be reproduced at will, was felt by all who used thermometers, and an important practical proposal to secure this desideratum was made in 1694 by Carlo Renaldini, a former member of the Accademia del Cimento. and professor of mathematics in Padua. At that date, and in the eightieth year of his age, he published a work on natural philosophy, in which he suggested taking the melting-point of ice and the boiling-point of water for two fixed points of thermometer scales, and dividing the space between them into twelve equal parts. This truly admirable proposition was not appreciated by his contemporaries who did not wholly believe in the constancy of these temperatures, and it was