on the Height of the Barometer in different Latitudes. 79 
Mean observed 
Latitude corre- 
sponding. 
Limits of the Zone of Lati- Mean observed 
tude N. and S. Pressure. 
in. 
‘ 29-821 
equatorial zone .. 
Lat. 5° to 15°, mean of : 
N. and S. zones .. eae) 
Zones 15° to 25° lat... 30:030 
Zones 25 to35 .... 30°125 
Zones 35 to40 .... 29-934 
Lat. 5° N. to 5° S., the ; 
“The following set of observations (made with no care, and with a 
bad barometer,) by Mr. MacHardy, surgeon of the Mountstewart El- 
phinstone, in its last voyage homewards, at my request, also confirm 
the equatorial depression : 
No of M bserved M bserved 
vie eet a ee Degree 
in. 
Dat OL tO OY Sa, a. 8 29°821 | ea. 
Best Dh Stee, « 5 29-802 9 20 
1d COL ZD aiec aire 6 29:960 19 41 
23 COLO OM cee teal O 30-085 31720 
** Not having Mr. MacHardy’s zero, I have made his equatorial re- 
sult correspond to Sir E. Ryan’s, by addition of a constant (+ 0-188). 
Sir E. Ryan’s depression is greater; Mr. MacHardy’s about the same 
which I first assigned (3 inch) from my own observations in my voyage 
out.” 
Extracts were also read of letters from C. Darwin, Esq., of Christ 
College, to Professor Henslow, containing an account of the geolo- 
gical phenomena of some parts of the Andes, 
Nov. 30.—Various presents were announced, and a paper by Pro- 
fessor Wallace of Edinburgh was read, containing geometrical theo- 
rems and formule, particularly applicable to some geodetical pro- 
blems. 
Afterwards Professor Airy stated his views and the results of his 
observations with reference to the supposed analysis of the solar 
spectrum into red, yellow, and blue, by Sir David Brewster, which 
supposition he conceived to be unfounded. Professor Airy, Mr. Roth- 
man, Mr. Peacock, and Mr. Power then gave an account of their ob- 
servations of the Aurora Borexlis of Nov. 18th. 
Dec. 14.—A communication by Mr. Potter, of Queen’s College, 
was read, containing an Explanation of the Rainbow on the doctrine 
of Interference, and referring especially to the Supernumerary Bows 
often seen within vivid displays of the rainbow, near its summit. It 
was shown that such additional bands would accompany the primary 
bow if the drops were of approximately equal size, and that the cir- 
