Facts form the Arcana of Nature. 89 



observed objects are in the same level or not. These errors 

 are usually remedied by an empirical law for terrestrial refrac- 

 tion ; but all such laws fail to apply in the varied states of 

 rarefaction or of moisture, in which the lower strata of the 

 atmosphere are found. 



3. An error of a single second in the celestial arc corre- 

 sponds to about one hundred feet on the surface of the Earth ; 

 and a long series of astronomical observations must be made 

 to obtain the latitude of any place true to a second. 



4. Local attraction of mountains, and variations in the 

 density of strata in the Earth are said to affect the accuracy 

 of the pendulum. 



5. It has been demonstrated that the figures of the 

 northern and southern hemispheres are dissimilar. 



6. No measurements have yet been attempted within such 

 distance of the poles as to preclude the possibility of an 

 extended polar radius, in excess of the supposed equatorial 

 radius. 



7. Some of the earlier observations made by the French 

 astronomers, gave results directly contrary to Newton's theory. 



8. Unaccountable discrepancies have been noted in results 

 of previous admeasurements of degrees on reversing the 

 course of the ship from which the observations have been 

 taken. 



9. Analysis of the theory of rate of transmission of light 

 may affect the time of high noon recorded, to a degree imper- 

 fectly provided for by previous empirical conclusions. 



Noting how rare it is — if not in practice impossible — in 

 land surveys by successive operators, though using approved 

 instruments, to maintain lengthened parallels, the accuracy 

 of sea measurements must ever be doubtful. Moreover, Sir 

 John Herschel admits that " a more exact knowledge of the 

 physical structure and figure of the Earth, and of the niceties 

 of astronomy, may render a different mode of computing 

 latitudes necessary." Thus, this eminently scientific astro- 

 nomer does not bar entrance on the path of knowledge 

 by asserting perfection of existing theories, or the infalli- 

 bility of the conclusions of our early and justly renowned 

 philosophers. 



Our task shall be to demonstrate that there exists, to say 

 the least, a difference of opinion amongst astronomers, 

 mathematicians, geologists, and philosophic reasoners, as 

 to the accuracy of our early philosophic theories respect- 

 ing the figure and structure of the Earth, and its im- 



