Philosophical Transactions. 133 



of soft iron, depends, as Mr. Barlow has advanced, on extent of surface, 

 and is wholly independent of the masSj except a certain thickness of the 

 iron, amounting to about two-tenths ot an inch, which is requisite for the 

 complete developement of its attractive energy. 



xi. Notice respecting a Volcanic Appearance in the Moon, in a 

 Letter addressed to the President. By Captain Henuy Kateh, 

 F.R.S. 



We have heard of volcanos in the moon, but when we con- 

 sider the fallacies to which observations of her surface are 

 liable, even when made with the most experienced eyes and 

 perfect instruments, we are induced to doubt the identity of 

 most of these appearances with terrestrial volcanic phenomena, 

 and to applaud Captain Kater for the caution shewn in the 

 title of this letter, where he calls the luminous spot which he 

 discovered, not a volcano, but a volcanic appearance. On 

 Sunday evening, the 4th of February, 1821, the moon being 

 two days old, and the evening clear, Captain Kater observed 

 a luminous spot in the dark part of her orb ; its appearance 

 was that of a small nebula, subtending an angle of three or 

 four seconds, and of variable brightness. " A luminous 

 point," says our author, " would suddenly appear in its centre, 

 and as suddenly disappear, and these changes would some- 

 times take place in the course of a few seconds. On the 5th, 

 6th, and 7th, it was again observed, but not afterwards." We 

 should have mentioned that the telescope which Captain Kater 

 used was a Newtonian, of 6^ inches aperture, with a power of 

 seventy-four. An engraving accompanies this paper. 



xii. A farther Accouiit of Fossil Bones, discovered in Caverns., 

 enclosed in the Limestone Rocks at Plymouth. By Joseph 

 WiiiDBEY, Esq. 



We have already given the essence of this paper ; it includes 

 Mr. Whidbey's account of the situation of the caverns, and Sir 

 Everard Home's catalogue of the relics, which we think are 

 not quite properly called fossil bones ; this, however, might 

 easily be determined by chemical analysis. They are deposited 

 in the museum of the College of Surgeons. 



xiii. On the Aeriform Compounds of Charcoal and Hydrogen, 

 with an account of some additional Experiments on the Gases 

 from Oil and from Coal. By William Henry, M.D. 

 F.R.S., 8iX. 



The labours of Dr. Henry have tended more perhaps than 

 those of any other individual to elucidate the nature and pro- 



