679 



back upon itself. Phenomena perfectly analogous to those observed 

 in frogs, may be produced in warm-blooded animals, by the action 

 of inverse currents ; they continue, however, for a much shorter 

 time, especially if the vitality of the animal is very great. These 

 phenomena clearly belong to the nerve, and have their origin in the 

 relation, the nature of which is yet undetermined, which exists be- 

 tween nervous influence and the action of the electric current ac- 

 cording to the direction of that current. Thus a limb traversed by 

 the direct current may be compared to a limb fatigued by repeated 

 efforts; the inverse current may be supposed to act in an opposite 

 manner, and during its passage, the nen/ous force may accumulate 

 in the nerve. The facts here recorded may establish a fresh con- 

 nection between nervous influence and the passage of the electric 

 current according to its direction. 



The sixth series treats of the laws of the electric discharge of the 

 Torpedo and other electrical fishes, and of the theory of the pro- 

 duction of electricity in these animals. Irritations applied to any 

 point of the body of an electrical fish are transmitted by the nerves 

 to the fourth lobe of the brain, and are then followed by the elec- 

 tric discharge : the nervous action by which this discharge is de- 

 termined under the influence of the will resides in that fourth, or 

 electrical lobe of the brain ; for after the three superior cerebral 

 lobes have been removed, the torpedo can still give the shock, either 

 voluntarily, or by external irritations. The separation of the two 

 electricities which takes place in the cells of the electrical organ, 

 under nervous influence, are instantaneously reunited by the dis- 

 charge. The strength of the current obtained during the discharge 

 is proportional to the length of the cellular prisms included in the 

 closed circuit. The author concludes that the nervous force in- 

 creases independently of the will with every increase in the activity 

 of the functions of circulation and of respiration, and of every act 

 of nutrition, and also under the influence of certain agents intro- 

 duced into the'system. 



The seventh and last series treats of the relation that exists be- 

 tween the intensity of the electric current and that of the corre- 

 sponding physiological efl'ect. A detailed account is given of the 

 apparatus employed, and of the method of experimenting, which 

 the author had recourse to in his researches on this branch of the 

 subject. The amount of the contractions produced in muscles under 

 different circumstances of electric excitation is stated in a table 

 which closes the paper. 



2. " On diff^erent properties of Solar Radiation, producing or pre- 

 venting a deposit of Mercury on Silver Plates coated with Iodine, or 

 its compounds with Bromine or Chlorine, modified by coloured glass 

 media and the vapours of the atmosphere." By A. C. Claudet. 

 Communicated by Sir David Brewster, K.H., D.CX., F.R.S., See. 



At an early period of the study of photography, it Avas observed 

 that the red, orange and yellow rays are endo^ved with antagonistic 

 powers, preventing and destroying the action produced by white 



