Colonel Beaufoy on the Diurnal Variation qftlie Needle. 179 
The small Island of Pianosa, immediately adjacent to Elba, 
now entirely uninhabited, might be cultivated to great advan- 
tage. The ancient roads still remain, as also the ruins of baths. 
It has a great extent of land fit for the plough ; 600 head of 
cattle might find pasture ; and the olive and vine thrive well. 
Napoleon had begun to repair the harbour, and build a fort to 
protect it from the Algerines, and at the same time to clear out 
the fountains still in existence. Now, however, all these im- 
provements are abandoned, and Pianosa remains uninhabited. 
Art. XXXIV. — Qiiarterly Abstract of the Diurnal Variation 
of the Magnetic Needle. By Colonel Beaufoy, F. R. S. 
Monthly mean Variation of the Magnetic Needle, 
Variation West. 
1817. 
' 1818. 
•1819. 
1 
C Morning, 
24° 31' 16" 
24° 34' 40" 
24° 32' 33" 
Aug. 
J Noon, 
24 42 51 
24 45 58 
24 42 49 
1 
(^Evening, 
24 33 45 
24 37 50 
24 34. 24 
1 
f Morning, 
24 33 02 
24 34 29 
24 32 29 
Sept. 
Noon, 
24 41 36 
24 45 22 
24 41 35 
i 
[ Evening, 
24 34 38 
24 37 28 
24 33 27 
\ 
r Morning, 
24 31 06 
24 35 36 
24 33 27 
Oct. d 
Noon, 
24 40 46 
24 43 28 
24 40 08 
i 
^ Evening, 
... 
Art. XXXV. — P7'Oceedings of the Royal Society of Edin- 
burgh. 
Nov. 15. 1819. Al. Paper by Dr Brewster was read on the 
subject of Circular Polarisation^ a name by which he proposes 
to distinguish" the phenomena first discovered by M. Arago, 
along the axis of Rock Crystal, afterwards analysed by M. Biot, 
and subsequently discovered by MM. Biot and Seebeck in seve- 
ral fluids. M. Biot had shewn, that in some specimens of rock 
crystalj a certain succession of tints was produced by turning 
the analysing prism direct from Right to Left, while in other 
specimens, the same succession was developed by turning the 
