96 THE HAMILTON ASSOCIATION 
of his life. He fitted up three contiguous houses owned by him, 
making them his observatory, workshop, engraving and printing 
office, and library. Hovel was an extraordinary man. He made 
his own instruments, engraved his own maps, and printed his obser- 
vations with his own hands. On the 26th of September, 1679, a 
vicious servant wickedly sat Hovel’s observatory on fire. Although 
most of his important works had been already printed and distribu- 
ted, the loss of his instruments and many papers caused him much 
grief, and hastened his death. His ‘‘ Selenography” appeared in 
1647. ‘The telescope he used magnified from thirty to forty diame- 
ters, and from his observations he engraved a map shewing two 
hundred and fifty lunar formations. ‘The chief lunar formations he 
named after the earthly formations he fancied they most resembled. 
The lunar Alps and Apennines, and four of the lunar promontories, 
retain the names he gave them; and the term JZave used by him to 
designate the dark lunar plains has since remained in common use. 
He called these plains seas, he says (‘‘ wet? er sie mit nichts anderm 
besser su vergleichen wisse”), because he knew nothing better to hken 
them to. For more than a century Hovel’s map was the best map 
of the moon, 
The first telescopic observers soon found: the lunar hemisphere 
turned earthward is always the same, or nearly the same. The diff 
erence there is, is due to libration, and its maximum amount is not 
a forty-ninth of the moon’s circumference, or more exactly is 7 
degrees, 53 minutes of lunar measurement. ‘To that extent only the 
moon changes the face turned earthward. The rest of her sphere is 
hidden forever from mortal sight. Hovel was first to explain that 
libration in longitude is due to the fact, the moon rotates on her axis 
at a uniform rate, while her movement of translation varies in velocity 
with her varying distance from the earth. Galileo had already found 
out that there is a similar libration in latitude, due to the moon’s 
axis of rotation not being exactly perpendicular to the plane of her 
orbit. 
In 1651, J. B. Riccioli, a member of the Society of Jesus, com- 
piled a lunar map noteworthy chiefly from its nomenclature. In lieu 
of Hovel’s names, he designated the craters and places marked on 
his map after names of eminent mathematicians and astronomers. 
A French astronomer archly says: ‘ Riccioli shrewdly avoided the 
