404 On the relation of Pressure to Density. 



fers less from that on the opposite hemisphere. Hence the 

 constant H, which in the above analysis was supposed to be in- 

 dependent of p, must, in order to take into account the effect of 

 this distribution of pressure, be regarded as an unknown function 

 of p. The law of IMariotte requires that this function should be 



H 

 of the form — , and that the repulsive action from the individual 



P 

 atoms should not be of sensible magnitude. The small amount 

 of this repulsion in aeriform bodies may well be attributed to 

 the comparatively large mutual distances of the atoms. It is 

 clear that a repixlsion varying inversely as the fourth power of 

 the distance, if sensible between neighbouring atoms in a 

 gaseous substance, would be enormously great if the same 

 substance were reduced to a liquid or solid state. 



This law of the increase of the repulsion of aggregation with 

 diminution of density, seems to account for a phsenomenon 

 otherwise very difficult to explain, viz. the great development 

 of repulsive action in the attenuated tails of comets, the effects 

 of which were so signally exhibited in the recent instance of Do- 

 nati's comet. 



In liquid and solid bodies, on the contrary, by reason of the 

 much greater contiguity of the atoms, the repulsive action from 

 the individual atoms becomes very energetic, while for the same 

 reason the condensations due to an aggregation of atoms may 

 be so far increased, that the pressure about any atom on which 

 they impinge may either be distributed uniformly, or may 

 accumulate on the side opposite to that of incidence, and thus 

 the repulsion be converted into attraction. It is also conceivable 

 that under these circumstances the molecular action, whether 

 repulsive or attractive, may be nearly proportional to the number 

 of atoms in a given space, and that for, at least, small variations 

 of the density of the medium, the quantity H is very nearly 

 constant. The law connecting the pressure and density in 

 liquid and solid bodies would, under this limitation, be expressed 



tr 



by the formula j5 = ^ . p^ + C. 



This theory enables us to conceive how a gaseous body, by 

 being greatly compressed, may be converted into a liquid. 



Cambridge Observatory. 

 May 18, 1859. 



