132 



Sir J. HerschelVs address 



not justify us in referring the observed effect to an unknown, and, so 

 far as we can see, an inconceivable cause, when this is at hand, ready 

 to account for the whole effect. 



I say, in the nature of a vera causa, since each particular star must 

 of necessity have some parallax. Every real, existing, material body, 

 must enjoy that indefeasible attribute of body, viz. definite place. 

 Now place is denned by direction and distance from a fixed point. 

 Every body, therefore, which does exist, exists at a certain definite 

 distance from us and at no other, either more or less. The distance 

 of every individual body in the universe from us is, therefore, neces- 

 sarily admitted to be finite. 



But though the distance of each particular star be not in strictness 

 infinite, it is yet a real and immense accession to our knowledge to 

 have measured it in any one case. To accomplish this, has been the 

 object of every astronomer's highest aspirations ever since sidereal 

 astronomy acquired any degree of precision. But hitherto it has 

 been an object which, like the fleeting fires that dazzle and mislead 

 the benighted wanderer, has seemed to suffer the semblance of an ap- 

 proach only to elude his seizure when apparently just within his 

 grasp, continually hovering just beyond the limits of his distinct ap- 

 prehension, and so leading him on in hopeless, endless, and exhaust- 

 ing pursuit. 



The pursuit, however, though eager and laborious, has been far 

 from unproductive, even in those stages where its immediate object 

 has been baffled. 



The fact of a periodical fluctuation of some kind in the apparent 

 places of the stars was recognized by Flamsteed, and erroneously 

 attributed to parallax. The nearer examination of this phenomenon 

 with far more delicate instruments, infinitely greater refinement of 

 method, and clearer views of the geometrical relations of the sub- 

 ject, rewarded Bradley with his grand discoveries of aberration and 

 nutation, and enabled him to restrict the amount of possible parallax 

 of the stars observed by him within extremely narrow limits. 



Bradley failed to detect any appreciable parallax, though he con- 

 sidered 1" as an amount which would not have escaped his notice. 

 And since his time this quantity has been assumed as a kind of con- 

 ventional limit, which it might be expected to attain, but hardly to 



