86 Prof. Leslie oii the Theory of' Compreasiwi applied to 



tience : the contraction and subsequent dilatation in the stem, 

 from abstracting and restoring the pressure of nine-tenths of an 

 atmosphere, amounts to 3 or 4 inches, and is rendered visible at 

 the distance of several benches in a large class-room, by help of 

 a drop of quicksilver resting on the top of the aqueous column. 



I have likewise had constructed by our ingenious young op- 

 tician Mr John Adie, a large and delicate instrument, suggest- 

 ed by the plan of Oerstedt, and capable of extensive application. 

 It beai's safely a pressure of 12 or 15 atmospheres, and not only 

 measures easily the contraction of different fluids, but serves to 

 indicate the various compressibility of solid substances. From 

 a series of experiments which I have instituted, I may venture 

 to anticipate the detection of some interesting and important 

 facts in the economy of Nature. 



The theory of the compression of bodies, carried to its full 

 extent, might give rise to several bold but striking speculations 

 regarding the internal constitution of our globe. Let the den- 

 sity of any substance, at a depth corresponding to the distance 

 X from the centre in miles, be denoted by J, (that at the surface 

 being assumed the unit), and the radius and the modulus of 

 elasticity expressed by r and m. Since the power of internal 

 gravitation is directly as the distance from the centre, it will 



be elsewhere demonstrated *, that Hyp. Losj. d = —^ 5 or, 



adopting common logarithms,, and inserting the numerical va- 

 lues, 



39562 — ^-2 



For Atmospheric Air, this ^rmula becomes 



3956^ — ^2 



Log. d=z 

 passes : 

 Log. d 



91090 

 For pure Water, it passes into 



39562 — ^* 



2415707 



And for White Marble, the Jbrmula is, 

 J 3956^--£f 



• See Elements of Natural Philosophy, voL ii. 



