60 Britain's Heritage of Science 



Halley succeeded Waller as Professor of Geometry at 

 Oxford in 1678, and Flamsteed as Astronomer Royal in 

 1720. When he arrived at Greenwich, he found most of 

 the instruments removed, being the private property of his 

 predecessor. He procured some new ones, and began the series 

 of observations of the moon, the continuance and improve- 

 ment of which has always been the special care of the Royal 

 Observatory. But the age at which he took over his duties 

 prevented his making much progress. 



Halley 's activity covered a large range of subjects, and 

 proved him to be a man of extensive knowledge and great 

 versatility. He investigated, independently of Mario tte, 

 the diminution of the pressure of air as we rise above the 

 surface of the earth, and gave the correct formula for 

 calculating differences in altitude from the barometric 

 records; he observed the aurora borealis, and connected 

 it with terrestrial magnetism by noting that the highest 

 point of the arch lies in the magnetic meridian. He gave 

 the generally accepted explanation of the cause of the 

 trade winds, but was less successful in his attempts to 

 improve the construction of thermometers; he was the 

 first to give the formula which connects the position of 

 objects and images formed by lenses ; he formed an esti- 

 mate of the quantity of water vapour which enters the 

 atmosphere by the action of solar heat on the oceans; he 

 wrote on the effect of the refraction of air on astronomical 

 observations, worked out the method of deducing the 

 distance of the sun from observations on the transit of 

 Venus, and made valuable contributions to the method of 

 calculating logarithms. He improved the construction of 

 diving bells, and was the originator of " life statistics." 

 There are few men who can show a finer record of scientific 

 activity. 



Halley was succeeded at Greenwich by Bradley (1692- 

 1762), to whom, according to the astronomer Delambre, 

 we owe the accuracy of modern astronomy. Bradley was 

 a nephew of John Pond (1669-1724), a clergyman who had 

 erected an astronomical observatory at his rectory of Wan- 

 stead in Essex, and done some meritorious work on the 

 satellites of Saturn and Jupiter. After graduating at Oxford, 



