A42 On the Quantity of Carbonic Acid Gas [Nov. 



at noon this powerful agent of nature is at his height, and hence 

 at this time may be supposed to exert his maximum energy ; 

 whatever, therefore, is under his immediate influence, must now 

 be supposed to be affected most strongly, and if the hypothesis 

 be correct,* that nervous action is so, it is perhaps easy to 

 account for many important phenomena which it presents, and, 

 among others, that of the greater elicitation f of carbonic acid 

 at noon, respiration being considered as under its immediate 

 influence. 



Of the immediate operations, however, of the sun, or minor 

 agencies under his direction, upon the nervous system, we know 

 nothing, as every thing connected with this part of our frames 

 is buried in the most profound obscurity. To refer, therefore, an 

 animal function or operation to this system, is in other words to 

 confess our ignorance of its nature ; and I consider it better to 

 do this than to run the chance of falling into error myself, and 

 of misleading others by a demonstration that in the present state 

 of our knowledge must be purely hypothetical. It is possible 

 also that the laws I have attempted to establish may depend upon 

 some idiosyncrasy, or suite of habits, peculiar to myself, and 

 may not be general. If they do exist, no doubt they are liable 

 to be modified in no small degree by habit, and even perhaps 

 totally subverted. Others, however, must decide this. With 

 respect to myself, I can only say that I have no doubt of their 

 existence. At all events, speculations would be premature on a 

 subject so slenderly founded as the ipse dixit of a single indivi- 

 dual ; and hence I shall defer my opinion till I have searched 

 into the matter further myself, and beard the observations of 

 others. Should they be established, I flatter myself they will 

 throw no inconsiderable light on some important points in phy- 

 siology and pathology. 



The instrument with which these experiments were made is ex- 

 tremely simple, and the mode of using it may perhaps be learned 

 by a mere reference to the figure [Plate XIII] . Its whole capacity 

 to B is exactly 25 cubic inches of water at 60 ; of these 2 cubic 

 inches are occupied by the neck, which is accurately graduated 

 into tenths of a cubic inch. When used, it is filled with water, 

 and a bladder, C, containing the respired air is screwe'd on, as 

 represented in the figure; it is then fixed'in the stand; and by 

 turning the stop-cocks, G and H, the water is permitted to run out 



* Arc not all the most powerful agents in nature, as heat, light, electricity, 

 magnetism, &c. which appear tn influence si> immediately and energetically 

 animal life, directed and governed, with respect to their periodical changes, 

 by the earth's motions on ils axis and in its orbit, which act only by placing it 

 in different position with respect to the sun ? 



+ Not ils formation: this is probably only a common chemical process, 

 The regulation of the degree, &c. of its formation is to be understood. 



