Formation of Compound or Twin Crystals. 277 



remarkable for its simplicity, that they are either Spheres or Sphe- 

 roids. 



A theory of later date,* but certainly not an improvement on the 

 last, gives to all simple atoms a Tetrahedral form, from combina- 

 tions of which solids, the molecules of compounds result. 



A fourth,! and that which embraces among its advocates the 

 greater part of the Chemists of the day, is founded on the supposi- 

 tion that the atoms of the elements are spheres and those of com- 

 pound bodies, an aggregation of these spheres. 



Without jemarking on any of these theories at present, I shall se- 

 lect from them, what appears to be correct and reply to the rest in 

 the course of the communication. 



The simplicity of the hypothesis of Wollaston, that the molecules 

 of matter are either spheres or spheroids, and its capability with 

 some modifications of explaining the numerous facts in Natural Phi- 

 losophy and Natural History, as also its consistency, at least, with 

 the principles of Chemical Science, seem to render its correctness 

 highly probable. 



It may be objected to it, that a permeation of the molecules by 

 one another, or an intimate union of them, is required in order to 

 form the molecules of compounds ; that is, a combination in which 

 the molecules of the elements, (Hydrogen and Oxygen for instance, 

 in water,) unite in a manner which may be represented by the com- 

 bination of two globules of mercury. As a consequence of this sup- 

 position, what are called atoms, are in fact not atoms, but on the 

 contrary either infinitely divisible particles, or '\{ finitely, capable of 

 exceedingly minute division, as is evinced in every instance of the 

 action of chemical affinity. The former is the most probable sup- 

 position. If it be advanced, that we cannot conceive of matter 

 with such a quality, equally imperfect, it may be replied, are our 

 powers of conception with regard to the existence of the Creator of 

 matter. The argument against the infinite divisibility of matter 

 which has been derived from the limits of vaporization, and that also 

 founded on observations of the eclipses of Jupiter's satellites, are not 



* By J. G. Macvicar, in a work entitled " Inquiries concerning the medium of 

 Light andthe form of its molecules." 8vo. 132pp., London, 1834. 



t This general theory admits of a great variety in its particulars and at present 

 is in a very indefinite state. An attempt to systematize it, has however been late- 

 ly made by M. Gaudin, who has published on the subject in the Revue Encyclope- 

 dique, Nov., 1833, Paris. 



