1814.] on the Cause of Chemical Proportions. 175 



is rather, I think, that the atoms are of unequal sizes ; and the size 

 may be in direct proportion to the weight, or otherwise. There 

 can, in fact, be only three suppositions on all this subject :— 

 1. That the sizes are all the same. 2. That the sizes are as the 

 weights. 3. That the sizes are unequal, but not as the weights. 

 My system is not restricted to any of these suppositions ; but if any 

 one can show that the regular organization of bodies is inconsistent 

 with one or other of these suppositions, it mvist, of course, be 

 rejected. Till that is done, one is about as plausible as another. 



It is rather amusing to me to observe the different manners in 

 which a cursory view of the atomic system strikes different persons. 

 Dr. Thomson was the first who, from some hints I gave him, 

 published an outline of the system in the third edition of his 

 chemistry. He used the phrase density of the atoms indifferently 

 for weight of the atoms, thereby implying that all atoms are of the 

 same size, and differ only in density ; but he has since very pro- 

 perly discontinued the use of the phrase. Tliis also appears to be 

 the notion of Berzclius. On the other hand, Dr. Bostock seems to 

 think (see Kich. Jour. vol. xxviii. p. 292) that the sizes of atoms 

 must be in direct proportion to their iveights. 



Dr. Berzelius thinks it necessary that when an atom of A com- 

 bines with an atom of B, it must touch it. We shall agree in this 

 mode of expressing the fact ; but our ideas may differ materially 

 wiih regard to the signification. The contiguous atoms of all 

 elastic fluids touch each other by means of thin atmospheres of 

 heat : I neither know nor admit of any other sort of contact. The 

 solid impenetrable matter, if there be such, constitutes the centre 

 of the atom, never comes into contact with that of any other, as far 

 as is known ; because it appears to be impossible to deprive bodies of 

 their heat. The atoms of bodies may, therefore, co-exist at various 

 distances ; in the solid and liquid forms they are comparatively 

 near, and in the elastic form distant; but in all the forms they are 

 subject to variation, in this respect, from temperature and pressure. 

 It is prol>able that the atoms of oxygen gas might be condensed into 

 a volume, so that their distance should not exceed that of oxygen 

 and hydrogen in an atom of steam, and yet not unite chemically so 

 as to change their form. Hence it should seem that tiie notion of 

 particles touching each other is not a sufficient criterion of chemical 

 union. In elastic fluids chemical union is best conceived, I think, 

 from the circumstance of two or more atoms of A and B uniting so 

 as to form a common centre of repulsion. 



With regard to the figure of atoms. Dr. Berzelius observes, that 

 a compound atom cannot be considered as spherical, but that an 

 elementary atom may be taken as such. Here, again, we should 

 understand one anotlicr, whether so/id corpuscle is meant, or solid 

 corpuude nnileil lu an atmosphere (f heat, when we speak of an 

 atom. If the former, then it is clear that compound atoms cannot 

 be spherical ; nor do I see any reason sufficient for supposing all 

 •imple atoms to be so; those of hydrogen may be sphericaL 



