D. Hector. — The Earth's Motion. 513 



space is another flagrant instance of the reification of con- 

 cepts." It would appear, however, that his strictures apply 

 not to the arguments for the possibility of transcendental 

 space, but to the arguments that we can have, under our 

 present limitations, any practical acquaintance with such 

 space. 



Art. LI. — The Equatorial Component of the Earth's Motion 



in Space. 



By Douglas Hector. 



[Bead before the Wellington Philosophical Society, 11th February, 1902.] 



Attempts have been made from time to time to find the 

 velocity of the earth — or, rather, the solar system — in space 

 by observing the proper motions of stars. Methods have also 

 been suggested that depend on the relative motions of the 

 earth ana ether. The following method, however, I have not 

 seen described anywhere, although it seems extremely simple. 

 If a rotating body moves along a path in the plane of its 

 equator, it is evident that a point on its surface moves faster 

 relatively to space on one side of its path than on the other ; 

 but an acceleration is proportional to the rate of change of 

 velocity, so that the point should undergo an alternating 

 acceleration. 



u = 



Let V = tangential velocity of the point P in space, 

 velocity of earth's centre in space, and v = rotational velocity 

 of P. Then, resolving along the tangent, we get V = v — u 

 sin. 6. If /is the acceleration of P along the tangent, 

 , dV d0 



7 — ~dt = ~ u di cos - & = —uw cos. 0. 

 33 



