EXAMPLES OF THE EXPLANATION OF LAWS. 341 



The reality of the power being thus proved, its agency explains a great 

 variety of apparently anomalous phenomena ; of which I select the follow- 

 ing from Dr. Brown-Sequard's Lectures on the Nervous System: 



The production of tears by irritation of the eye, or of the raucous mem- 

 brane of the nose ; 



The secretions of the eye and nose increased by exposure of other parts 

 of the body to cold ; 



Inflammation of the eye, especially when of traumatic origin, very fre- 

 quently excites a similar affection in the other eye, which may be cured by 

 section of the intervening nerve ; 



Loss of sight sometimes produced by neuralgia, and has been known 

 to be at once cured by the extirpation (for instance) of a carious tooth ; 



Even cataract has been produced in a healthy eye by cataract in the 

 other eye, or by neuralgia, or by a wound of the frontal nerve; 



The well-known phenomenon of a sudden stoppage of the heart's action, 

 and consequent death, produced by irritation of some of the nervous ex- 

 tremities ; e. ff., by drinking very cold water, or by a blow on the abdo- 

 men, or other sudden excitation of the abdominal sympathetic nerve, 

 though this nerve may be irritated to any extent without stopping the 

 heart's action, if a section be made of the communicating nerves ; 



The extraordinary effects produced on the internal organs by an exten- 

 sive burn on the surface of the body, consisting in violent inflammation 

 of the tissues of the abdomen, chest, or head, which, when death ensues 

 from this kind of injury, is one of the most frequent causes of it; 



Paralysis and anaesthesia of one part of the body from neuralgia in an- 

 other part ; and muscular atrophy from neuralgia, even when there is no 

 paralysis ; 



Tetanus produced by the lesion of a nerve. Dr. Brown-Sequard thinks 

 it highly probable that hydrophobia is a phenomenon of a similar nature ; 



Morbid changes in the nutrition of the brain and spinal cord, manifest- 

 ing themselves by epilepsy, chorea, hysteria, and other diseases, occasioned 

 by lesion of some of the nervous extremities in remote places, as by worms, 

 calculi, tumors, carious bones, and in some cases even by very slight iri-i- 

 tations of the skin. 



§ 4. From the foregoing and similar instances, we may see the impor- 

 tance, when a law of nature previously unknown has been brought to light, 

 or when new light has been thrown upon a known law by experiment, of 

 examining all cases which present the conditions necessary for bringing 

 that law into action ; a process fertile in demonstrations of special laws 

 previously unsuspected, and explanations of others already empirically 

 known. 



For instance, Faraday discovered by experiment, that voltaic electricity 

 could be evolved from a natural magnet, provided a conducting body were 

 set in motion at right angles to the direction of the magnet ; and this he 

 found to hold not only of small magnets, but of that great magnet, the 

 earth. The law being thus established experimentally, that electricity is 

 evolved, by a magnet, and a conductor moving at right angles to the direc- 

 tion of its poles, we may now look out for fresh instances in which these 

 conditions meet. Wherever a conductor moves or revolves at right angles 

 to the direction of the earth's magnetic poles, there we may expect an evo- 

 lution of electricity. In the northern regions, where the polar direction is 

 nearly perpendicular to the horizon, all horizontal motions of conductors 



