^68 Prof. De la Rive on Electricity. 



The direction of the current indicated, that it was the inferior 

 surface of the electrical organ that was the source of the negative 

 electricity, and the superior of the positive. Respecting the 

 anatomical structure of this organ, Dr Davy has furnished a de- 

 tailed description, whence he concludes, that it is not muscular, 

 but that the columns of which it is composed are formed of ten- 

 dinous or nervous fibres, filled with a gelatinous fluid, and a great 

 quantity of water, which may be disengaged by evaporation. 



II. On Terrestrial Magnetism, as connected with the Origin and For- 

 mation of the Earth, 



Besides atmospheric and animal electricity, there is a third 

 natural source, on which it may be interesting to give a few de- 

 tails. We allude to that better known under the name of terres- 

 trial magnetism, and which consists in the probable existence of 

 electrical currents under and very near to the surface of our globe. 

 In former times, terrestrial magnetism was supposed to be con- 

 nected with two magnetic poles, which received a local habita- 

 tion at no great distance from the geographic ones ; but since 

 we have succeeded in demonstrating the identity of magnetism 

 and electricity, and, more especially, since we have seen that 

 electrical currents can impart to the magnetic-needle a determi- 

 nate direction, the much more probable supposition of terrestrial 

 electrical currents has been embraced, to explain the directive 

 action of the globe upon the magnetic-needle. The extensive 

 and successful study of terrestrial magnetism, seems more fa- 

 vourable to this hypothesis than to any other ; and it seems to 

 accord in the most remarkable manner with the constitution of 

 the globe, and with the phenomena that are taking place be- 

 neath and upon its surface. Some slight details will, we trust, 

 demonstrate the accuracy of this assertion. 



There are two circumstances which, having been carefully ob- 

 served in many different places of the earth's surface, have elu- 

 cidated the theory of terrestrial magnetism, viz. the direction of 

 the attraction exercised upon the needle by the earth, and the 

 intensity of that attraction. On the former of these circumstan- 

 ces, as is well known, hangs two results, first the inclination or 

 dip, the angle at each spot formed by the needle, and the per- 

 pendicular ; and secondly, the declination^ or the angle which 

 this same direction forms with the astronomical meridian, or true 



