ige Captain Kater on a lunar volcano. 
increased light of the moon, than to the diminished action of 
the volcano. 
I have the honour to be, 
Dear Sir, &c. &c. 
Henry Kater 
To Sir Humphry Davy, Bart. 
P. R. S. &c. 
P. S. Since the preceding letter was written, I have ascer- 
tained that the spot in which I observed the volcanic appear- 
ance is that named Aristarchus. This spot was particularly 
examined by Hevelius, who calls it Mons Porphyrites, and 
who considers it to be volcanic. If his drawings are to be 
relied upon, it has undergone a considerable change in its 
appearance since his time. 
Sir William Herschel has recorded in the Philosophical 
Transactions an observation of three volcanoes, which he 
perceived in the moon, April 19th, 1787, at io h . $6 m , side- 
real time. One of these, which he says showed “ an actual 
eruption of fire or luminous matter,” was distant from the 
northern limb of the moon 3'. 57", 3, the diameter of the 
burning part being not less than 3". I find that this obser- 
vation was made about 9 o’clock in the evening, when the 
moon was not quite two days old ; and from the situation of 
the spot described by Sir William Herschel, I have no doubt 
of its being the same that I have noticed. 
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