267 



Mr. Bell concludes this paper with some remarks upon the use of 

 the plexus formed on both sets of nerves, and on their association 

 upon the integuments. In regard to the plexuses, he considers them 

 as concerned in associating the functions of distinct muscles ; and in 

 reference to the surface of the body, he remarks, that although the 

 principal office of its nerves is to convey impressions to the senso- 

 rium, yet, on the other hand, the condition of the mind is often 

 forcibly communicated to the skin. Hence the striking union of the 

 branches of the fifth pair with the portio dura of the seventh pair hi 

 the integuments of the head and face. 



On the Constitution of the Atmosphere. By John Dalton, Esq. 

 F.R.S. 8(C. Communicated January 12, 1826. Read February 24, 

 1826. [Phil. Trans. 1826, Part II. p. 174.] 



The object of this paper is to examine the consequences as respects 

 the proportion of the component parts of the atmosphere simultane- 

 ously existing at different heights in one vertical column, which 

 would follow from the atomic theory, on the supposition of a finite 

 number of atoms existing in corporeal bodies, and of such a law of 

 repulsion prevailing among those of elastic fluids, as Sir Isaac Newton 

 appears to have supposed, in which the repulsive power of each par- 

 ticle terminates at the particles immediately adjacent. It is well 

 known that when two or more mutually inactive gaseous fluids are 

 mixed, each distributes itself uniformly through the whole space oc- 

 cupied, and each sustains a part of the whole pressure retaining them, 

 proportioned to its density. This is a necessary consequence of the 

 mutual inelasticity and independence of the gaseous atmospheres 

 with respect to each other. Each exerts the whole mechanical force 

 its quantity will allow, without regard to the others ; and the sum 

 of all these forces in the state of equilibrium counterbalances the 

 total pressure. 



This uniformity of density, however, is only a consequence of the 

 assumed principle, where the gases occupy such small spaces as we 

 can command in our experiments, in which the total pressure may 

 be regarded as uniform, in a vertical as well as in a horizontal di- 

 rection ; it is otherwise when we regard a column of indefinite height, 

 or one prolonged to the limit of the atmosphere, a limit at which 

 the weight of a single particle is in exact equilibrio with the repul- 

 sion between two contiguous ones. It is this case which the author 

 considers in the paper before us. He supposes, for simplicity, two 

 atmospheric columns, one of hydrogen, and the other of carbonic 

 acid, each supporting at its base a pressure of 30 inches of mercury; 

 of such height as to reach to the respective limits of each atmo- 

 sphere, divided each by partitions into cells of equal magnitude, at 

 first insulated from each other, then made to communicate, and finally, 

 the cells to be withdrawn, and a free communication established be- 

 tween every part of the two columns : and from an analysis of what 

 passes in the act of communication, and from the general principles 



