THE MOON. 77 



whose results were confirmed four years later by 

 Zantedeschi, another Italian. The most import- 

 ant work in this direction was accomplished 

 by the present Earl of Rosse (born in 1840), 

 who in the years 1869-72 believed himself to 

 have measured the lunar heat ; but these con- 

 clusions were not altogether confirmed by the 

 observations of Dr Otto Boeddicker (Lord Rosse's 

 astronomer), during the total lunar eclipse of 

 October 4, 1884. Further investigations on this 

 subject were afterwards made by Samuel Pierpont 

 Langley (1834-1906), of Alleghany, and by his 

 assistant, Frank Very. 



The motion of the Moon and its perturbations 

 were made the subject of deep study by the 

 famous Pierre Simon Laplace (1749-1827), the 

 contemporary of Herschel, and the worthy suc- 

 cessor of Newton. He devoted much attention 

 to the secular acceleration of the Moon's mean 

 motion, a problem which had baffled the greatest 

 mathematicians. After a profound discussion he 

 found, in 1787, that the average distance of the 

 Earth and Moon from the Sun had been slowly 

 increasing for several centuries, the result being 

 an increase in the Moon's velocity. In the third 

 volume of the ' Mecanique Celeste' Laplace 

 worked out the lunar theory in great detail, 

 although he calculated no lunar tables. After 



