VENUS ON THE SUN'S FACE. 69 



The two observers who saw the transit end earliest 

 and latest could do the like. 



Speaking generally, and neglecting all the com- 

 plexities which delight the soul of the astronomer, this 

 is Delisle's method of utilising a transit. It has ob- 

 viously one serious disadvantage as compared with the 

 other. An observer at one side of the earth has to 

 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 observes, 

 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 ob- 

 server must know so certainly in what exact longitude 

 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's 

 Land, Chatham Island, and the wilds of Siberia. 



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

 astronomer 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 difficulties 



