84 LIGHT SCIENCE FOR LEISURE HOURS. 



have to remain at their several stations for a long time 

 before the transit takes place several months, at least 

 so that they may accurately determine the latitude 

 of the temporary observatories they will erect. This 

 is a work requiring skilled observers and recondite pro- 

 cesses of calculation. Hence it is that the cost of 

 sending out these observing parties is so considerable. 



The only English party which will apply Halley's 

 method of observation is the one which will be sta- 

 tioned at Crozet Island or Kerguelen Land. This part 

 of their work will be comparatively easy, the method 

 only requiring that the duration of the transit should 

 be carefully timed. In fact, one of the great advan- 

 tages of Halley's method is the smallness of the ex- 

 pense it involves. A party might land the day before 

 the transit and sail away the day after, with results at 

 least as trustworthy as those which a party applying 

 Delisle's method could obtain after several months of 

 hard work. It is to this, rather than any other cause, 

 that the small expense of the observations made in 1769 

 is to be referred. And doubtless had it been decided 

 by our astronomical authorities to apply Halley's 

 method solely or principally, the expense of the transit- 

 observations would have been materially lessened. 

 There would, however, have been a risk of failure 

 through the occurrence of bad weather at the critical 

 stations ; whereas now as other nations will doubt- 

 less avail themselves of Hallev's method the chance 



