76 



INTUODUCTIOX. 



thermometer, it must not be forgotten to put into 

 the water a good thermometer, graduated by Reau- 

 mur's scale, to correct the specific gravity observed, 

 by the annexed table.* 



* Care must be taken 

 during the observation, that 

 no considerable bubbles of 

 air hang to the areometer, 

 and they must be removed, 

 either by taking out the in- 

 strument, or by clearing 

 them away with a hair-pen- 

 cil. 



Supposing now, that, in order to sink the are- 

 ometer to the mark, it has been necessary to add 

 1^ i^ n^ the specific gravity of the water ==1,023.5, 

 if the temperature of the water at the time was + 

 14°, 5 R, we have to add to the value found 

 0,00137, + 0,00017 = 0,00154, by which we have 

 (1,023.5 + 0,00154) = 0,02504; if the temperature 

 had been -1-7" 3 R, we should have had 1,0235 — 

 0,00113=1,02237 for the specific weight of the sea- 

 water of 10° R. This examination of the sea-water 

 to discover the quantity of salt contained in it, may 

 be of advantage to navigation, as it indicates the 

 influence of large rivers, at a great distance from 

 land ; on a voyage to the north, this examination 

 is especially to be made in the vicinity of large 

 masses of ice, to determine whether the water 



