86 LIGHT SCIENCE FOR LEISURE HOURS. 



show how much of the blame of that unfortunate cen- 

 tury 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 disk. This at least was what Halley and 

 Delisle both suggested as desirable. Unfortunately, 

 Yenus had not been consulted, and when the time of 

 the transit came she declined to enter upon or leave 

 the sun's face in the manner suggested by the astrono- 

 mers. Consider, for example, her conduct when en- 

 tering on the sun's face : 



At first, as the black disk of the planet gradually 

 notched the edge of the sun's disk, all seemed going on 

 well. But when somewhat more than half of the 

 planet was on the sun's face, it began to be noticed 

 that Yenus was losing her rotundity of figure. She 

 became gradually more and more pear-shaped, until at 

 last she looked very much like a peg-top touching with 

 its point the edge of the sun's disk. Then suddenly 

 " as by a lightning-flash," said one observer the top 

 lost its peg, and then gradually Yenus recovered her 

 figure, and the transit proceeded without further 

 change on her part until the time came for her to 

 leave the sun's face, when similar peculiarities took 

 place in a reversed order. 



Here was a serious difficulty indeed. For when 

 was the moment of true contact ? "Was it when the 



