on a new Hydrostatic Balance, 109 
of the first. The larger pea will then indicate the units of weight, 
and the smaller the tenths or hundredths. The same object 
might also be obtained by suspending the pea to the middle of a 
Vernier-scale. 
The instrument, and its necessary appendages, are arranged in 
a small box, so as to be very convenient, and very portable, 
Your Committee, after a due consideration and an actual trial 
of this apparatus, are of opinion, that, for facility and rapidity 
of operation, it has the advantage over every other that has hi- 
therto been proposed for the same purpose; and they therefore 
cheerfully recommend it to the attention of the Academy. 
They propose that it should be named Lukens’s Hydrostatic 
Balance. 
All which is respectfully submitted. 
Wixturam Maciure. 
R. M. Patrerson. 
Isaac LEa. 
XXIV. Description of a Hydrostatic Balance, by which the 
Specific Gravities of Minerals may be ascertained without 
Calculation, By Bens. H, Coates, M.D. Reud June 16, 
1818*, 
Tae present instrument (see Plate II. fig. 2,) has arisen from 
one lately presented to the Academy, in which the common steel- 
yard is employed for this purpose. 
The object of the alteration is, without rendering the instru- 
ment more complicated, or more troublesome in its application, 
to save the labour and inconvenience of calculation. By neans 
of it, the specific gravity of a mineral may be ascertained in a few 
moments, and without pen and ink, or any other assistance than 
a cup of water. With the-aid of the neatness and convenience 
of the instrument on which it is grafted, it is hoped to be a prac- 
tical saving of time and labour to the mineralogist. 
The lever resembles that of a common steelyard, and is con- 
trived to balance exactly, by making the shorter end wider, and 
with an enlargement at the extremity. The upper edge of each 
limb is rectilinear, and free from notches, for the sake of accu- 
racy in adjusting the weights. 
The shorter end is undivided; but on the longer i is inscribed 
a scale, of which every division, reckoning from the extremity of 
the lever, is marked with a number, which is the quotient of the 
length of the whole scale, divided by the distance of the division 
from the end. Thus, at half the length is marked the number 2, 
* From the Journal of the Academy of Natural Scicnces of Philadelphia, 
Vol. 1. Part I. 
at 
