150 BULLETIN OF THE 



of the spectral lines, aud speaks familiarly of the diatomic molecule.* 

 It is true that the "atom " is properly a physical and not a chemical 

 unit, since it can never be reached by any possible reactions of 

 affinity or of decomposition. But if the term is to be still retained 

 in chemical nomenclature, it should always be understood in its 

 merely etymological sense of the " undivided," and not in its more 

 popular sense of the uncompounded. 



3. The Fallacy of Kinematic Theories. 



After this rather labored effort to approximate to some definite 

 conception of the physical nature of the two types of invisible or 

 elementary motion — displayed in the atomic revolutions or oscilla- 

 tions generating radiant undulations of the sether, and in the mole- 

 cular flights and encounters generating the thermo-dynamic pres- 

 sures of gaseous fluids, — let us consider what countenance these 

 forms of motion may be supposed to lend to a kinematic theory of 

 universal force. 



It is important here to notice that by experiments on the sensi- 

 ble vibrations of bodies, — as of tuning-forks and pneumatic dia- 

 phragms, — translatory motions of approach and recession have been 

 produced in light bodies. The "attractions" or "repulsions" have 

 been shown to depend on the amplitudes of the oscillation, and the 

 ratio of the wave-lengths to the surfaces of action ; as also on the 

 symmetrical concurrence or reversal of the phases of vibration in 

 two confronting systems.f 



*Prof. George F. Barker in his excellent presidential address before 

 the Chemical Section of the American Association at Buffalo, on the theme — 

 " The Molecule and the Atom," referring to the constitution of hydrochlo- 

 ric acid, repeats the common view : " hence a molecule of hydrogen is com- 

 posed of two atoms." (Proceed. Am. Assoc. August, 1876 : p. 95.) 



fDr. Jules Guyot. Des Mouvements de I'Air etdes Pressions de I'Air 

 en Mouvement. 8vo. Paris, 1835. 



Prof. Frederick Guthrie. "On Approach caused by Vibration." 

 L. E. D. Phil. Mag. Nov. 1870: vol. XL, p. 354. (From his tuning-fork 

 experiments, the author ventures the bold and startling induction: "In 

 mechanics — in nature — there is no such thing as a pulling force.") 



Prof. C. A. Bierknes of Christiania, Norway. Hydro-dynamic expert 



