66 LIGHT SCIENCE FOR LEISURE HOURS. 



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 stationed 

 at Mauritius, under Lord Lindsay. 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 advantages 

 of Halley's method is the smallness of the expense 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 occur- 

 rence of bad weather at the critical stations ; whereas 

 now as other nations will doubtless avail themselves 

 of Halley's method the chance that the transit-obser- 

 vations will fail through meteorological causes is very 

 largely diminished. Science will owe much to the 

 generosity of England in this respect. 



It is, indeed, only recently that the possibility of 

 applying Halley's method has been recognised. It 

 had been thought that the method must fail totally in 



