Chap. 2.] Fahrenheit's Hydrometer. 423 



fhould be marked upon it, to prevent its being for- 

 gotten. The inftrument is then plunged into diftilled 

 water ; and by putting weights into the bafon p E, it 

 is made to fink as far as the grain of fmalt (a). The 

 weights which were made ufe of to produce this im- 

 merfion, added to the weight of the hydrometer, gives 

 exactly the weight of the volume of water meafured 

 by the inftrument. By repeating the fame operation 

 upon any other fluid, the weight of the volume of that 

 fluid meafured by the hydrometer, may be known with 

 equal exactnefs. Hence it follows, that the quantity 

 of thefe two volumes are equal, becaufe they are mea- 

 fured by the fame inftrument: the difference of their 

 weight then will give the difference of their fpecific 

 gravity, or the relation between their denfities. To 

 determine this relation exactly, the following propor- 

 tion muft be obferved : The fpecific gravity of the 

 proved liquor, is to that ofdiftilled water as the weight 

 of a volume of that fluid meafured by the hydrometer, 

 is to the weight of the volume of water alfo meafured by 

 it. If the fpecific gravity of the one is known exactly, the 

 fpecific gravity of the other' may be determined by it, 

 and alfo that of all other fluids which are proved in the 

 fame manner. 



The whole of what has been advanced in this chap- 

 ter, and in that of the firft book upon fpecific gravity, 

 may be briefly fummed up in the following propofi- 

 . lions; Firft, when two bodies are equal in their magni- 

 tude, bulk, or volume, their fpecific gravities arc to 

 each other as their denfities. So that one body has 

 twice the fpecific gravity of another, when it has twice 

 the denfity of that other body comprized in the fame 

 fpace or magnitude. 



Secondly, when two bodies lofe an equal weight in 



the fame fluid, they have the fame magnitude or folid 



E e 4 contents, 



