Previously to ordering these globes, I exposed to a like degree of fire, a square mass of iron, and another of lead of two inches diameter, and found, by reiterated essays, that lead heated and cooled in much less time than iron. I made the same experiment on red copper, and that required more time to heat and cool than lead, and less than iron. So that of these three matters, iron appeared the least accessible to heat, and, at the same time, that which retained it the longest. From which I learn that the law of the progress of heat in bodies was not proportionable to their density, since lead, which is more dense than iron or copper, nevertheless heats and cools in less time than either. As this object appeared important, I was induced to have these globes made, and to be more perfectly satisfied of the progress of heat in a great number of different matters, I always placed the globes at an inch distance from each other, before the same fire, or in the same oven, 2, 3, 4, or 5, together with a globe of tin in the midst of them. In most of my experiments I suffered them to be exposed to the same active fire till the globe of tin began to melt, and at that instant they were all removed, and placed on a table in small cases. I suffered them to cool without moving, often trying whether I could touch them, and the moment they left off burning, and I could hold them in my hands half a second, I marked the time which had passed since I drew them from the fire. I afterwards suffered them to cool to the actual temperature, of which I endeavoured to judge by means of touching other small globes of the same matters that had not been heated. Of all the matters which I put to the trial, there was only sulphur which melted in a less degree of heat than tin, and notwithstanding its disagreeable smell I should have taken it for a term of comparison, but being a brittle matter which diminishes by friction, I preferred tin, although it required nearly double the heat to melt. Having heated together bullets of iron, copper, lead, tin, gres, and Montbard marble, they cooled in the following order: _So as to be held in the hand _To actual temperature._ for half a second._ Min. Min. Tin in 6-1/2 In 16 Lead in 8 In 17 Gres in 9 In 19 Common marble in 10 In 21 Copper in 11-1/2 In 30 Iron in 13 In 38 By a second experiment with a fiercer fire, sufficient to melt the tin bullet, the five others cooled.