342 INDUCTION. 



will produce electricity; horizontal wheels, for example, made of metal; 

 likewise all running streams will evolve a current of electricity, which will 

 circulate round them ; and the air thus charged with electricity may be 

 one of the causes of the Aurora Borealis. In the equatorial regions, on 

 the contrary, upright wheels placed parallel to the equator will originate a 

 voltaic circuit, and water-falls will naturally become electric. 



For a second example, it has been proved, chiefly by the researches of 

 Professor Graham, that gases have a strong tendency to permeate animal 

 membranes, and diffuse themselves through the spaces which such mem- 

 branes inclose, notwithstanding the presence of other gases in those spaces. 

 Proceeding from this general law, and reviewing a variety of cases in which 

 gases lie contiguous to membranes, we are enabled to demonstrate or to 

 explain the following more special laws: 1st. The human or animal body, 

 when surrounded with any gas not already contained within the body, 

 absorbs it rapidly ; such, for instance, as the gases of putrefying matters : 

 which helps to explain malaria. 2d. The cai'bonic acid gas of effervescing 

 drinks, evolved in the stomach, permeates its membranes, and rapidly spreads 

 through the system. 3d. Alcohol taken into the stomach passes into vapor, 

 and spreads through the system with great rapidity (which, combined with 

 the high combustibility of alcohol, or in other words its ready combination 

 with oxygen, may perhaps help to explain the bodily warmth immediately 

 consequent on drinking spirituous liquors). 4th. In any state of the body 

 in which peculiar gases are formed within it, these will rapidly exhale 

 througli all parts of the body ; and hence the rapidity with which, in certain 

 states of disease, the surrounding atmosphere becomes tainted. 5th. The 

 putrefaction of the interior parts of a carcass will proceed as rapidly as 

 that of the exterior, from the ready passage outward of the gaseous prod- 

 ucts. 6th. The exchange of oxygen and carbonic acid in the lungs is not 

 prevented, but rather promoted, by the intervention of the membrane of 

 the lungs and the coats of the blood-vessels between the blood and the air. 

 It is necessary, however, that there should be a substance in the blood with 

 which the oxygen of the air may immediately combine ; otherwise, instead 

 of passing into the blood, it would permeate the whole organism: and it is 

 necessary that the carbonic acid, as it is formed in the capillaries, should 

 also find a substance in the blood with which it can combine ; otherwise it 

 would leave the body at all points, instead of being discharged through 

 the lungs. 



§ 5, The following is a deduction which confirms, by explaining, the em- 

 pirical generalization, that soda powders weaken the human system. These 

 powders, consisting of a mixture of tartaric acid with bicarbonate of soda, 

 from which the carbonic acid is set free, must pass into the stomach as 

 tartrate of soda. Now, neutral tartrates, citrates, and acetates of the al- 

 kalis are found, in their passage through the system, to be changed into 

 carbonates; and to convert a tartrate into a carbonate requires an addi- 

 tional quantity of oxygen, the abstraction of which must lessen the oxygen 

 destined for assimilation with the blood, on the quantity of which the 

 vigorous action of the human system partly depends. 



The instances of new theories agreeing with and explaining old empiri- 

 cisms, are innumerable. All the just remarks made by experienced per- 

 sons on human character and conduct, are so many special laws, which 

 the general laws of the human mind explain and resolve. The empirical 

 generalizations on which the operations of the arts have usually been 



