80 LIGHT SCIENCE FOR LEISURE HOURS. 



bring his observations into comparison with, those 

 made by an observer at the other side of the earth. 

 Each uses the local time of the place at which he ob- 

 serves, and it has been calculated that for the result 

 to be of value there must not be an error of a single 

 second in their estimates of local time. Now, does the 

 reader appreciate the full force of this proviso ? Each 

 observer must know so certainly in what exact longi- 

 tude he is, that his estimate of the time when true noon 

 occurs shall not be one second wrong ! This is all 

 satisfactory enough in places where there are regular 

 observatories. But matters are changed when we are 

 dealing with such places as Woahoo, Kerguelen Land, 

 Chatham Island, and the wilds of Siberia. 



Here, however, as in so many other cases, the as- 

 tronomer must take what he can get and be thankful. 

 If Nature insists on not revealing her secrets unless 

 astronomers will betake themselves to all manner of 

 desert and uncanny places, all astronomers can do is 

 to face with boldness the difficulties thus placed in 

 their way, and to do their utmost to bring them into 

 complete subjection. 



In the coming transit there are many such diffi- 

 culties to be encountered. In fact, it is almost impos- 

 sible to conceive a transit the circumstances of which 

 are more inconvenient. On the other hand, however, 

 the transit is of such a nature that if once the prelimi- 

 nary difficulties are overcome, we can hope more from 



