FREE BOOKS

Author's List




PREV.   NEXT  
|<   236   237   238   239   240   241   242   243   244   245   246   247   248   249   250   251   252   253   254   255   256   257   258   259   260  
261   262   263   264   265   266   267   268   269   270   271   272   273   274   275   276   277   278   279   280   281   282   283   284   285   >>   >|  
of the smallest decimals? On the one hand, mathematical formulae, deduced from the principle of universal attraction; on the other hand, certain irregularities observed in the returns of the moon to the meridian. An observing geometer who, from his infancy, had never quitted his chamber of study, and who had never viewed the heavens except through a narrow aperture directed north and south, in the vertical plane in which the principal astronomical instruments are made to move,--to whom nothing had ever been revealed respecting the bodies revolving above his head, except that they attract each other according to the Newtonian law of gravitation,--would, however, be enabled to ascertain that his narrow abode was situated upon the surface of a spheroidal body, the equatorial axis of which surpassed the polar axis by a _three hundred and sixth part_; he would have also found, in his isolated immovable position, his true distance from the sun. I have stated at the commencement of this Notice, that it is to D'Alembert we owe the first satisfactory mathematical explanation of the phenomenon of the precession of the equinoxes. But our illustrious countryman, as well as Euler, whose solution appeared subsequently to that of D'Alembert, omitted all consideration of certain physical circumstances, which, however, did not seem to be of a nature to be neglected without examination. Laplace has supplied this deficiency. He has shown that the sea, notwithstanding its fluidity, and that the atmosphere, notwithstanding its currents, exercise the same influence on the movements of the terrestrial axis as if they formed solid masses adhering to the terrestrial spheroid. Do the extremities of the axis around which the earth performs an entire revolution once in every twenty-four hours, correspond always to the same material points of the terrestrial spheroid? In other words, do the poles of rotation, which from year to year correspond to different stars, undergo also a displacement at the surface of the earth? In the case of the affirmative, the equator is movable as well as the poles; the terrestrial latitudes are variable; no country during the lapse of ages will enjoy, even on an average, a constant climate; regions the most different will, in their turn, become circumpolar. Adopt the contrary supposition, and every thing assumes the character of an admirable permanence. The question which I have just suggested, one of the
PREV.   NEXT  
|<   236   237   238   239   240   241   242   243   244   245   246   247   248   249   250   251   252   253   254   255   256   257   258   259   260  
261   262   263   264   265   266   267   268   269   270   271   272   273   274   275   276   277   278   279   280   281   282   283   284   285   >>   >|  



Top keywords:
terrestrial
 

surface

 

correspond

 

spheroid

 

notwithstanding

 

Alembert

 

mathematical

 

narrow

 

universal

 
extremities

adhering

 

masses

 

formed

 

principle

 

formulae

 

twenty

 

revolution

 
performs
 
deduced
 
entire

attraction

 

movements

 

Laplace

 

returns

 

supplied

 

deficiency

 

examination

 

nature

 
neglected
 

currents


exercise
 
suggested
 

influence

 
atmosphere
 
fluidity
 
observed
 

irregularities

 

question

 
average
 
character

constant
 

smallest

 

climate

 
regions
 
contrary
 

supposition

 

circumpolar

 

admirable

 

country

 

permanence