74 LIGHT SCIENCE FOR LEISURE HOURS. 



applying Halley's method has been recognised. It 

 had been thought that the method must fail totally in 

 1874. But on a more careful examination of the 

 circumstances of the transit, a French astronomer, 

 M. Puiseux, was enabled to announce that this is not 

 the case. Almost simultaneously the present writer 

 published calculations pointing to a similar result ; but 

 having carried the processes a few steps further than 

 M. Puiseux, he was able to show that Halley's method 

 is not only available in 1874, but is the more powerful 

 method of the two. 



Unfortunately, there is an element of doubt in the 

 inquiry of which no amount of care on the part of our 

 observers and mathematicians will enable them to get 

 rid. We refer to the behaviour of Venus herself. It 

 is to the peculiarity we are now to consider that the 

 ^wasz'-failure of the observations made in 1769 must be 

 attributed. It is true that Mr. Stone, the eminent 

 first-assistant at the Greenwich Observatory, has man- 

 aged to remove the greater part of the doubts which 

 clouded the results of those observations. But not 

 even his skill and patience can serve to remove the 

 blot which a century of doubt has seemed to throw 

 upon the most exact of the sciences. We shall now 

 show how much of the blame of that unfortunate 

 century of doubt is to be ascribed to Venus. 



At a transit, astronomers confine their attention to 

 one particular phase the moment, namely, when 

 Venus just seems to lie wholly within the outline of 

 the sun's disc. This at least was what Halley and 



