On Specific Gravity. 125 
resistance to the immersion of the same body in different 
fluids, is, therefore, the same as ascertaining the weights of 
bulks of those fluids, equal to the body, and, of course, to 
each other. And if one of the liquids be water, dividing by i its 
weight, the weight of the others, gives their specific gravities. 
If the stopple be so proportioned, as to lose da one thou- 
sand grains, by immersion in water, division is unnecessary, 
as the weight of the ees will be obtained in grains, which 
are thousandths by the premises. A metallic mass, of the 
same weight as the stopple exactly, may be employed as its 
counterpoise. 
In these experiments, the liquid should be as near 60° of 
Fahrenheit’s Thermometer as possible. 
On the application of the Sliding Rod measurement, in Hy- 
drometry. 
There is, in my opinion, no mode of measuring fluids, 
heretofore contrived, so accurate and convenient, as tha‘ 
which I have employed in my Eudiometers. [ allude to the 
contrivance of a rod, or piston, sliding through a collar of 
leathers into a tube, and expelling from it any contained fluid, 
‘quantities: meacured.b y degrees marked upon the rod ; and 
ascertained, with additional accuracy, by means of a vernier. 
One of the most advantageous applications of the mechan- 
ism alluded to, is, in ascertaining specific gravities, in the 
case either of liquids or solids. To assay liquids which are 
not nar et I have employed two instruments like that re- 
in the following figure, severally graduated to 100 
Gators and furnished with a — by which those degrees 
may be divided into tenths, and each scale made equivalent 
to 1000 parts. 
