J. D. Dana on Cohesive Attraction. 383 



to the general law of mutual influence, or tendency to equilibri- 

 um, and no other law is required to explain a change of size. 



same 



of different sizes (or in other words of different temperatures), 

 there would be between them a tendency to equilibrium of size 

 (or in common language, to a mean temperature) ; and thus this 

 simple law of mutual influence will explain enlargement or con- 

 traction from variations of temperature ; and the variations from 



different 



a mean size 



substances mutually act on one another, will be specific heat. 

 The change of form and axes in molecules dependent on change 

 of temperature, will be a consequence of change of size, accord- 

 ing to some law yet unascertained. 



This view, for which we are indebted to Mr. Whelpley, ex- 

 plains expansion without recourse to any intervening ether, or 

 any imponderable agent, excepting the general force of attraction. 

 Admitting these conclusions, it will follow that the forms de- 

 duced for molecules are their actual forms. We confidently be- 

 lieve it will soon be shown that this change of size and attendant 

 changes in pulsating force, will sufficiently explain the physical 



effects of heat.* 

 A molecule according to these views, is spherical or spheroidal 



in form : — 



It exerts attraction in every direction ; but this force on oppo- 

 site parts is so related that one molecule attracts another by one 

 side and repels it by the opposite (polarity) : — 



In solidification (and sometimes before ?) this attraction is axi- 

 ally polar ; it admits of various degrees of axial concentration or 

 diffusion, (<§> 7 to 12,) of acceleration or retardation of action, 

 ($ 15,) and of different degrees of radial force, which variations 

 take place under the general law of mutual influence, or tenden- 

 cy to an equilibrium : — 



This attraction acts by pulsations ; in solidification there are 

 also compound pulses (undulations in intensity) consisting of a 

 series of pulsations, and producing intermitted or seriate results 

 (cleavage), which results are in all cases specific; the same pul- 

 sations (the optic nerve being sensible to them) produce the 

 Phenomena of light : they are also a means of producing chemical 

 effects, especially when the pulsations exceed the rapidity of 

 those for light, (the chemical rays being those beyond the violet 

 ray or those which have been shown to be most rapid in vibra- 

 tion.) The a and § states of elements, or their passive and 



' The relations of heat and magnetic, are illumed }°"*^£'%± 

 «1 Tolume, by Prof. W. A. Norton, pp. 1 and 207; an.) some followmg pages 

 >Main an interesting memoir on heat and light by I rof. Draper. 



