142 



from Captain Kater's experiments, to consist in placing it in the 

 magnetic meridian, joining the opposite poles of a pair of bar mag- 

 nets, (they being in the same line,) and laying them flat upon the 

 needle, with their poles upon its centre ; then, having elevated the 

 distant extremities of the magnets, so that they may form an angle 

 of about 2 or 3 with the needle, they are to be drawn from the 

 centre to its extremities, carefully preserving the same inclination ; 

 and having joined the poles of the magnets at a distance from the 

 needle, the operation is to be repeated ten or twelve times upon each 

 surface. 



In needles from five to eight inches long, their weights being 

 equal, Captain Kater found their directive forces nearly as the lengths; 

 but in needles of nearly the same length and form, the directive force 

 is as the mass, and not dependent upon the extent of surface. 



Lastly, the author ascertained that the deviation of a compass 

 needle, occasioned by the attraction of soft iron, depends, as Mr. 

 Barlow has advanced, upon extent of surface, and is wholly inde- 

 pendent of the mass ; excepting that a thickness of the iron, amount- 

 ing to about two tenths of an inch, is requisite to the complete de- 

 velopment of the attractive energy. 



Notice respecting a Volcanic Appearance in the Moon. In a Letter ad- 

 dressed to the President. By Captain Henry Kater, F.R.S. Read 

 February 8, 1821. [Phil. Trans. 1821, p. 130.] 



This volcano was first observed by Captain Kater on Sunday the 4th 

 of February, the moon being then two days old, with a Newtonian 

 telescope of 6^ inches aperture, and a power of 74. The position of 

 the volcano is shown in an annexed drawing ; its appearance was 

 that of a small nebula, subtending an angle of 3 or 4 seconds, and 

 its brightness very variable. 



It was again observed on the evenings of the 5th and 6th, but was 

 then more faint, though occasionally exhibiting the appearance of a 

 luminous point, like a star of the 6th or 7th magnitude. Captain 

 Kater thinks that the distance of the volcano from the edge of the 

 moon was about one tenth of her diameter ; and the angle which it 

 formed with a line joining the cusps on the last-mentioned evening, 

 was about 50. On the 7th it was scarcely visible, in consequence, 

 probably, of the increased light of the moon. 



A Further Account of Fossil Bones discovered in Caverns inclosed in 

 the Lime-stone Rocks at Plymouth. By Joseph Whidbey, Esq. In 

 a Letter addressed to Sir Everard Home, Bart. V.P.R.S. Read 

 February 8, 1821. [Phil. Trans. 1821, p. 133.] 



These bones were found not far from those previously described 

 by Mr. Whidbey, and in a similar situation ; the cavern being en- 

 tirely inclosed in the surrounding rock, and without the smallest 

 appearance of any communication ever having existed with the sur- 



