56 HERSCHEL AND HIS WORK 



cavities in the moon are from ten to seventeen 

 thousand feet in depth, that they are surrounded by 

 a great rampart or wall, a hundred, two hundred, or 

 two hundred and fifty miles round, and that the 

 mountains which rise from the floor of the cavity 

 may be about a mile or a mile and a half high. 1 



His study of the moon's face led him, two years after, 

 to believe that, from his far-off station near Windsor, 

 to which he had then removed from Bath, he was 

 looking down one night into the depths of the boiling 

 crater of a volcano in the moon. A discovery so 

 singular was not a thing to publish till he had full 

 assurance of its accuracy. Four years after, he be- 

 lieved he had obtained evidence sufficient to warrant 

 publication. Others, well qualified to judge, were of 

 the same opinion. Among them was a gentleman 

 from the Gottingen Society, to which Herschel the 

 year before had taken the King's present of a 10-feet 

 reflector. Writing to a friend in Paris, that gentle- 

 man says : 



" May SO. 



" SIR, Mr. Herschel has lately made a discovery of 

 the greatest consequence, of which I have had the good 

 fortune to be an eye-witness. He had observed last 

 month, one or two days after the new moon, in the 

 dark part of it, three luminous points. Two of these 



1 Moretus is a circular depression 120 kilometres across (80 miles), 

 with an isolated mountain in the centre of nearly 7000 feet in height, 

 the most considerable of its kind on the moon (Atlas Photographique 

 de la Lune, Paris 1898, c. 56). The depths of the cavities are frequently 

 very great, Tycho, for example, 5500 metres, or nearly 18,000 feet 

 (c. 30, c. 55). Some of the mountain masses or tablelands are 5000 

 metres, 6600, and 7100, judging from the shadows they cast, or 16,000, 

 21,000, or 23,000 feet (c. 55, 56). 



