VENUS ON THE SUN'S FACE. 67 



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 I published calcu- 

 lations pointing to a similar result ; but having carried 

 the processes a few steps further than M. Puiseux, 

 I 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. I refer to the behaviour of Venus herself. It 

 is to the peculiarity we are now to consider that the 

 guasi-failure of the observations made in 1769 must be 

 attributed. It is true that Mr. Stone, the first-as- 

 sistant at the Greenwich Observatory, has managed 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 Delisle both 

 suggested as desirable. Unfortunately, Venus had not 



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