388 



Art. Xn'. Misctl/nneuus Intellige/ice. 

 I. Mechanical SclE^'CE. 



]■ N'ew hydrostatkal Balance, by Benj. H. Coates, M.D. — 

 This instrument is described in the Journal of the Philadelphian 

 Academy of Natural Sciences. It is an improvement on an 

 instrument before presented to the Academy, and the object in 

 view in making the alteration was to save the labour and 

 inconvenience of calculation. By means of it the specific 

 gravity of a mineral may be ascertained in a few moments, 

 and without pen or ink, or any other assistance than a cup of 

 water. 



The lever resembles that of a common steel-yard, and is 

 contrived to balance exactly, by making the shorter end 

 Avider, and with an enlargement at the extremity, (see fig. 2, 

 plate III.) The upper edge of each limb is rectilinear, and 

 free from notches, for the sake of accuracy in adjusting the 

 weights. 



The shorter end is undivided, but on the larger 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, at one third 3, at one-fourth 4, ^c. Also, at two- 

 thirds, the length is marked one and a half, at two-fifths two 

 and a half, ^c, and so of all the fractions sufficiently minutely. 

 These numbers extend as high as the specific gravity of 

 platinum. The pivot of the instrument represents unity, and a 

 notch is made at the farther end. 



In using this instrument, any convenient weight is suspended 

 by a hook from the notch at the end of the scale. The body 

 under examination is to be suspended to the other end by a 

 horse-hair, and moved along until an equilibrium is produced. 

 It is then, without altering its situation on the beam, to be 

 inamersed in water, and balanced a second time bv slidino- 



