THE COMING TRANSIT OF VENUS. 29 



On this point all doubts should have been very 

 quickly removed. For, almost simultaneously with 



able for applying Halley's method as the transit of 1874. So the 

 Astronomer Eoyal concluded. He did not enter into details, but after 

 summing up the evidence much as we have done above, he said " the 

 observable difference of duration in 187 4 will probably not be half of that 

 in 1882." It was in 1857 that he thus spoke; and he has never said a 

 word or written a line since that time implying that he had gone into 

 the details of the matter. When he next touched on the subject (in 1864) 

 he referred to the lecture of 1857 as showing the suitability of Halley's 

 method in 1882, and he left the transit of 1874 wholly unnoticed. 

 Again, in December 1868, he touched on the matter, simply saying that 

 Halley's method fails totally in 1874. That fatal lecture, or rather the 

 error suggested in the process of popularising the subject for that occasion, 

 led to so established a conviction as to the uselessness of Halley's 

 method in 1874, that it had never seemed worth while to re-examine the 

 matter. But now let us consider details a little, and see how the matter 

 will then appear. 



' In the first place, the transit of 1882 at once loses its apparent 

 superiority. The southern observer must have the sun moving from west 

 to east during the transit, or in other words, he must have the sun on 

 the night side (so to speak) of the sky. There is, of course, no night 

 near the Antarctic Pole on December 6, but at nominal midnight the 

 sun is at its lowest ; and the sun must be towards this part of his diurnal 

 course, if the observer is to get the advantage we are considering. There 

 is no known Antarctic station where this can be, the sun being also 

 fairly high at the beginning and end of the transit. This at once dis- 

 poses of the superiority of the transit of 1882. If an Antarctic station 

 is sought at all, there will be a hastening instead of a retarding of the 

 planet's transit, or an unfavourable point, as in the case of the earlier 

 transit. In reality, the loss thus accruing is found to be much more 

 serious in 1882 than the corresponding loss in 1874, when we inquire 

 into actual details. 



' But in 1874, as we have seen, there must be an unfavourable hastening 

 of Venus's motion as seen from a northern station ; and this hastening 

 seems to cancel the effect due to the lengthened transit-path. When we 

 inquire, however, to what extent this cancelling takes place, we at once 

 see that the Astronomer Kcyal was frightened away from Halley's 

 method without sufficient reason. He manifestly (see the italicised re- 

 mark quoted above) supposed that the duration would scarcely be in- 

 creased at all at the northern station. Let us see, however, whether 

 Mr. Proctor has been right or not in saying that the duration is con- 



