284 



SCIENCE. 



[Vol. II., No. 30. 



to a vertical plane containing the centre of gravity. 

 Taking a second marked spot in the plane thus 

 found, the operation is repeated, with the plane 

 horizontal. This gives a second plane through the 

 centre of gravity. A third operation, with the inter- 

 section of the two planes in the line de, locates the 

 centre of gravity. 



The kinetic theory of the specific heat of 

 solids. 



BV II. T. EDDY OF CINCINNATI, OHIO. 



Tnis pnper was based npon the well-known views 

 of lis autlior respecting the use to be made of the 

 different degrees of freedom of motion among the 

 atoms of solid bodies, in deducing a theory that will 

 explain their diverse powers of conducting heat, and 

 of transmitting or causing the transmission of radi- 

 ant energy. The theoiy is based upon the concep- 

 tion that all bodies are constituted of equal ultimate 

 atoms, whose combination, in different degrees of 

 freedom, in different molecules, gives rise to the char- 

 acteristic diffei'ences of elementary substances. This 

 paper shows that the same hypothesis would cause 

 solids, whicit are kept in equilibrium by radiation, to 

 be also in thermid equilibrium when brought into 

 contact; the eqviilibrium depending upon collisions 

 of the molecules. 



A kinetic theory of melting and boiling. 



BY H. T. EDDY OF CINCINNATI, OHIO. 



In a solid in which the molecules are evidently 

 held at nearly fi.xed mean distances by cohesive and 

 elastic forces, there are two kinds of partially con- 

 strained freedom of motion possible for each mole- 

 cule as a whole: first, a motion of its centre in a 

 small orbit of more or less irregular shape abotit a 

 mean position; and, second, a more or less irregular 

 pendular motion of oscillation about a mean direc- 

 tional position. Both of these motions can be treated 

 as vibratory motions; and the laws of force under 

 which the motions occur, though somewhat unlike, 

 have a general resemblance. 



Twro forms of apparatus for Boyle's law. 



BY B. F. THOMAS OP COLUMBIA, MO. 



These pieces are intended to enable one to adjust 

 with accuracy and ease the mass of air to be experi- 

 mented upon. 



V is an iron cistern into which the open or pressure 

 tube 0, the closed tube O, and the reversible air- 

 syringe S are screwed air-tight, and the cistern nearly 

 filled with mercury. The syringe being connected 

 for exhausting, and operated, air is withdrawn from 

 C, until the mercury sinks to the bottom of the open 

 tube, when air escapes from it, and rises through the 

 mercury. No more air can be withdrawn from C. 

 The mass of air remaining in Cwill evidently depend 

 on the difference iii depth of immersion of C and 0. 

 Let d = this difference, and let it be required to find 

 such a value of d as will permit just enough air to 

 remain in C to fill it from the zero of the scale, 



when at atmospheric pressure ff. Let L = length of 

 C from lop to zero, and let I' = the length from zero 

 to the opeji end of C. If now the mass of air whicU 



will fill the length Z at iZ be expanded to fill the length 

 I', the pressure//' at the bottom of C by Boyle's law is 



^ l+l' 



The pressure at the open end of O — H. The dif- 

 ference in pressure at the ends of C and is that 

 due to a column {d] of mercury. Hence B' = U — d. 



I^'' • , til' 

 Equatmg, II — d = j-v-.,- . . d= pirp- ■ 



On reversing the syringe, and forcing air in, the 

 mercury will be found to rise and stand at zero in 

 both tubes together. The demonstration is continued 

 by forcing in more air. 



A second form consists of two glass tubes con- 

 nected by a strong rubber tube, and momited on a 

 stand with scales. The closed 

 tube C is sealed into the screw- 

 cover of an iron cistern D. 

 Mercury being poured in, it will 

 expel the air in D, and rise in 

 an open screw-hole S in tlie 

 cover. The hole being sealed 

 by insertion of the screw, and 

 lowered, the air in C ex- 

 pands, filling C and Z). On rais- 

 ing O, tlie mercury rises, and 

 cuts off communication between 

 C and D, preventing the return 

 of some of the air. By making 

 D of proper volume, the desired mass of air will 

 remain in C. Let tde volume of C above the zero =: 

 F'. Let the entire volume of C — V, and the volume 

 of D above the open end of C= V". Following the 

 above steps it will be seen that a volume V at // be- 

 comes a volume F'+ V" at //'; also that a volume 

 F at // becomes a volume V at W. Hence the 

 proportions V : V : : F' : F' + F", .". V" = 



F' 

 (V — y)~y^- The use of the rubber tube is not 



new : the method of adjusting the air-mass is be- 



