SKETCH OFDIMITRI IVANOVICR MENDELEEF. 265 



gust, 1879, Mendeleef pointed out the relations ■wliic]i existed 

 between tlie density and the atomic weights of the elements; 

 these were subsequently more fully examined by Lothar Meyer, 

 and are embodied in the well-known curve in his Modern The- 

 ories of Chemistry. Similar relations have been observed in 

 certain other properties, such as ductility, fusibility, hardness, 

 volatility, crystalline form, and thermal expansion ; in the refrac- 

 tion equivalents of the elements, and in their conductivities for 

 heat and electricity; in their magnetic properties and electro- 

 chemical behavior ; in the heats of formation of their haloid com- 

 pounds ; and even in such properties as their elasticity, breaking 

 stress, etc." While one may be readily inclined and many have 

 been led to look for a connection between the periodic law and the- 

 ories of the unitary origin of matter, Mendeleef has not allowed 

 his studies in the subject to be embarrassed by any such pre- 

 possession. He said in his Faraday lecture : " The periodic law, 

 based as it is on the solid and wholesome ground of experimental 

 research, has been evolved independently of any conception as to 

 the nature of the elements ; it does not in the least originate in 

 the idea of a unique matter ; and it has no historical connection 

 with that relic of the torments of classical thought, and there- 

 fore it affords no more indication of the unity of matter, or of 

 the compound nature of the elements, than do the laws of Avo- 

 gadro or Gerhardt, or the law of specific heats, or even the con- 

 clusions of spectrum analysis." The periodic law is developed 

 in the author's Principles of Chemistry, which was first pub- 

 lished in 18G9, and appeared in a fourth edition, after a thorough 

 revision, with many important additions and modifications, in 

 1882. 



In a lecture before the Royal Institution in 1889, Mendeleef 

 sought to apply a broader generalization and to discover a harmoni- 

 ous law regulating both chemical and astronomical phenomena. 

 The immediate object of the lecture was to show that, starting 

 from Newton's third law of motion, it is possible to preserve to 

 chemistry all the advantages arising from structural teaching, 

 without being obliged to build up molecules in solid and motion- 

 less figures, or to attempt to ascribe to atoms definite limited 

 valencies, directions of cohesion, or affinities. He supposed that 

 harmonious order reigns in the invisible and apparently chaotic 

 motions of the universe, reaching from the stars to the minutest 

 atoms, which is commonly mistaken for complete rest, but which 

 is really a consequence of the conservation of dynamic equilibrium 

 that was discovered by Newton, and has been traced by his suc- 

 cessors as relative immobility in the midst of universal and active 

 movement. The unseen world of chemical changes was regarded 

 as analogous to the invisible world of the heavenly bodies, " since 



