There are likewise several chalybeat springs in the neighbourhood of Carlsbad; one at half a mile, and the other at two leagues distance from the town. Both of them seem to resemble the water of the Pohun spring at Spa; but are not near so strong. They do not use them medicinally on the spot; but they are brought to Carlsbad, and sold, in order to be drank with their wine. I am, My Lord, With the greatest respect, Your Lordship’s Most obedient humble Servant, Jeremiah Milles. Grosvenor-street, Jan. 19th, 1757. V. _An Essay towards ascertaining the specific Gravity of living Men. By Mr._ John Robertson, _F.R.S._ [Read Jan. 27, 1757.] SOME time last autumn I had occasion to draw up a few examples on the use of a table of the specific gravities and weights of some bodies. Among other things, that occurred then to me, I thought it might be useful to know the specific gravity of men. In order to make some experiments on this subject, I got a cistern made, of 78 inches in length, 30 inches wide, and 30 inches deep: it was constructed as near a parallelopiped as the workman could, to prevent tedious operations in computing the horizontal sections of the cistern by the surface of the water. I then endeavoured to find ten persons, such as I proposed to make the experiments withal; namely, two of six feet high, two of five feet ten inches, two of five feet eight inches, two of five feet six inches, and two of five feet four inches. One of each height I proposed should be a fat man, and the other a lean one; but I could not succeed in procuring such men; and, after waiting till near the middle of October, I was obliged to put up with such, as would submit themselves to the experiment at that season of the year. They were all labouring men, belonging to the ordinary of Portsmouth yard, and, except one or two of them, who were middling sized men, were for the most part very thin and slim made persons. I had also provided a sliding measure to take their heights, and scales to weigh them in. Every thing being prepared, each man stript himself in an adjoining room, and put on a pair of trowsers for decency’s sake: his height was first taken, then his weight, and then he immersed (fortified with a large dram of brandy). A ruler, graduated to inches, and decimal parts of an inch, was fixed to one end of the cistern, and the height of the water noted before a man went in, and to what height it rose when he ducked himself under its surface; and of these several observations is the following table composed.