438 PHILOSOPHICAL TRANSACTIONS. [aNNO IOQI, 



proportion of weight to water, the specific gravity of bodies may thence be 

 more exactly determined j counterfeits distinguished from genuine, and the 

 mixture of mineral particles in stone discovered. Archimedes first observed 

 that a body heavier than water, weighs less in water than in the air, by the 

 weight of as much water as is equal to it in bulk. The difference then of the 

 weights in air and water, gives the weight of so much water, and dividing the 

 greater number by the less, the quotient compared to unity, will be the propor- 

 tion of the weights of the solid body and water. 



The author having shown in what manner all solid bodies heavier than water 

 may be compared to one another, and not only their specific gravity, but their 

 qualities very often detected: he next considers, 1. How bodies lighter than 

 water may be examined in it, viz. by adding lead to wax or fir-wood, and sub- 

 ducting for the h^vy body so added. 2. How fluids, as mercury, or chemical 

 oils of cloves, &c. or bodies dissoluble in water, as sublimate, alum, vitriol, or 

 fragments of any brittle body, viz. by a small glass bucket or phial stopped, 

 which may receive these bodies, adding so much water as will fill the spatiola 

 of the fragments, up to the brim of the glass ; for which allowance must be 

 made in the computation of the weight, both in the air and water. 



Having examined bodies by water and oils, the author proceeds to examine 

 the weight of liquors, by weighing solids in them. For if a heavy body in 

 water lose so much of its weight as the quantity of fluid weighs that is of an 

 equal bulk with the body, the proportion of the weight of all fluids will be 

 easily obtained. Of waters, rain water seems the lightest, and scarcely 1000th 

 part difference discovered in any of them. This is particularly applied to the 

 famed water of the Ganges, though travellers assert an extraordinary lightness 

 in it. 



In the last place the bulk of solid bodies may be found out by this method. 

 For since a cubical inch of water weighs 256 gr. and as much of oil of turpen- 

 tine 221 gr. if a body of any magnitude, and irregular shape, lose so much 

 or more times that weight in water or oil, it is of a magnitude equal to one or 

 more cubical inches. 



On the Time and Place of Julius Ccesars Descent upon Britain. By Mr. 



E. Halley. N° IQS, p. 495. 

 The authors that mention this expedition with any circumstances, are Caesar 

 in his Commentaries, lib, 4, and Dion Cassius, in lib. 3g ; Livy's account being 

 lost, in whose 105th book might possibly have been found the story more 

 at large. It is certain that this expedition of Caesar's, was in the year of the 

 consulate of Pompey and Crassus, which was in the year of Rome 699, or the 



