J. D. Dana on Cohesive Attraction. 379 



We 



of layers of molecules takes place by an intermitted action ; that 

 is, with regular successive variations or pulses in the intensity of 

 the force of attraction. This intermitted action when reduced 

 to simply the adding of single layers in succession, becomes con- 

 tinuous. On these principles there might be every variety of 

 this quality in nature, and there should be no necessary con- 

 nection between cleavage and strength of attraction. We there- 

 fore infer that 



XVI. The action of cohesive attraction is often intermittent, 

 producing seriate results, (as exemplified in the cleavage of crys- 

 tals,) and the specific rate of intermittent action is different for 

 unequal axes* 



17. Cohesive attraction may be partly controlled in its results 

 by gravity, and by rate of solidification or of chemical combina- 

 tion. It is evident that in the cooling of a liquid mass, when 

 the temperature of solidification is reached, there will be num- 

 berless points throughout the mass where the molecules will 

 commence the process of crystallization; and acting together, 

 they would produce an aggregation of small crowded crystals or 

 grains, with no external regular forms, in other words, the gran- 

 ular structure. In cases of a crystallizing solution, the same re- 

 sult may happen, if the process be rapid. 



Again, a thin solution spread over a large surface, would pro- 

 duce crowded minute points; and if the solution be gradually 

 supplied, as the crystallization goes on. it is obvious that the mi- 

 nute points crowded together might elongate into crowded prisms, 



reproduction pro- 



successively.for the simple reason, of universal application, that re 

 duces temporary exhaustion, or, that force is exerted mteimittedly. 

 The putltJ „f molecular force is also an example ot ,, te n it > ac , on and 



must ife at t!le bas i s of the universal principle , on hi >•»$««* wi $ w « ™ JJ 



*"uden. The reality of this pulsation, ins.sted upon by Mr. J. U. WHeWe "> 

 1345 before his t Nation • and also by Faraday,* «M cannot doubt. The un- 

 W-4 theo^of l~h must be received as ™j£™£«» ^ ** ££,£ 

 ether that pulsates, it is molecular force which makes it pulsate, and this implies 



pulsating action in molecular force itself. ; n ,«,,mittent in intrnsitu I 



The attraction of cohesion is shown by cleavage to ^^^'ITSlSi 

 *e do not learn from it that there is any actual u.term.ssion of time 10 



^Ai^VTM^tt.tt P-llel stations which con- 



«* of alternations of two or more sets of plan* . I hue ™^ t] Jfi )etwe „ n £ 

 lenerally have their faces marked with «"* «rl,.c» «« ™£ " " n|]((ther lane 

 Plane replacing the edge, and either the face of the primary ^ b ^ ,. , £,„;„, 

 of the same secondary 8 Some octahedrons of fluor yjj^.fgj^ bow fre- 

 of minute cubes. These facts, and they are common and I weh Mow 



quent intermittent mode of action .n the *f*™*™' " f , "d an ! oscil atory com? 

 ftrife between different sets,) producing what has been called an J 



■naiioiT of planes. 



Rep. Proc. for 1845, and also this Jour . xlviii. :r* and ii Ser., ii, 401 

 * Phil. Mag., May, 1846, and this Jour., II Ser., n, 401. 



