8 W I LDE, Evolution of the Mental Faculties. 



of sense impressions, extending over many thousands of 

 years, is almost instinctive, and a long course of mental 

 training will yet be required before it is eradicated from 

 the civilised world. 



In my papers on the causes of the phenomena of 

 terrestrial magnetism no indication was given of the 

 source from whence the earth's magnetism might be 

 derived. I now avail myself of this opportunity to supply 

 the omission by assuming that the friction between" the 

 external and internal parts of the earth, rotating with a 

 differential motion, is competent to generate the necessary 

 quantity of electricity, as in the case of Armstrong's 

 hydro-electric machine. 



The like explanation is also applicable to account 

 for the generation of the electricity of the sun, by the 

 friction produced by the differential motions of its external 

 and internal regions and manifesting itself in the solar 

 corona. Moreover, the interruptions in the symmetry of 

 the corona are coincident with the discharge of elementary 

 vapours through sun-spot apertures, the greater amount 

 of asymmetry being also coincident with the maximum 

 period of sun-spot frequency. Hence the causal con- 

 nection existing between sun-spots, terrestrial magnetic 

 disturbances, and the display of electrical auroras in 

 comparatively low latitudes. 



The axial rotation of the moon during its synodical 

 revolution, by which it always presents the same part of 

 its surface to the earth, is so axiomatic that it might appear 

 almost superfluous to offer any further demonstration 

 of its reality beyond those already given by astronomical 

 writers. So slow, however, is the growth of scientific 

 ideas, that an individual examination of any large body 

 of conventionally educated persons, would show that 



