26 LIGHT SCIENCE FOR LEISURE HOURS. 



method. If this resulted from the simple preference of 

 Delisle s method, there would be little to say. Most 

 assuredly, speaking for myself, I should be very loth to 

 urge the advantages of Halley s method, if I found 

 against such a view the practical experience of those 

 astronomers who are continually testing the value of 

 various methods of observation. But the rejection of 

 Halley s method for the transit of 1874 was not origin 

 ally, and is not now, based on any objection to the 

 principle of the method, but on certain mathematical 

 considerations, which appeared to prove that the method 

 could not be advantageously applied in 1874, while it 

 could be applied successfully in 1882. It was accord 

 ingly reserved for the latter transit, and all the stations 

 for observing the transit of 1874 were selected with 

 special reference to the method of Delisle. 



Now it happened that early in 1869 I was attracted 

 to the examination of the subject of the coming tran 

 sits, by the circumstance that the investigation applied 

 to the matter by the Astronomer Eoyal had struck me 

 as imperfect in method. I was interested, viewing the 

 matter merely as a mathematical problem, to inquire 

 what corrections might occur if all the niceties of re 

 search of which the question admitted were applied 

 throughout the investigation. Working with this sole 

 object in view, I analysed the whole matter in two 

 independent ways, viz., first as a problem of calculation, 

 and secondly as a geometrical problem. The results, 

 perfectly concordant, differed so remarkably from those 

 published by the Astronomer Royal, that I was con- 



