VANES AND ANEMOMETER. lix 
ing of the Observatory. This vane indicated the direction of the lightest winds, 
and the direction of the wind was generally taken from it after November 13, 1844. 
On December 4, 1846, a light frame covered with oiled silk was substituted for the 
turkey feathers. The direction of the wind is indicated in this volume by the num- 
ber of the point of the compass, reckoning N = 0, E =8, S= 16, W = 24. 
101. The anemometer, the invention of Mr R. Antz, of Liverpool, was made by 
Messrs ADIE and Son, of Edinburgh; it occupies the north-east corner of the Obser- 
vatory. This instrument will be best under- 
stood by a reference to the annexed figure : 
@ is a cistern containing water to the level 6, 
¢ being a turn-cock for letting the water off 
to the exact level, and da glass-gauge to shew 
when the water becomes too low, from eva- 
poration or otherwise ; an inverted vessel ¢ 
is suspended in the water by a cord passing 
over the wheel 7, whose axle rests on friction- 
rollers at g and Ah; 7 isa spiral, which has a 
cord wrapped onit carrying a weight k, which 
balances the vessel e; J is a dial, graduated 
on the face near the circumference ; m an in- 
| dex, attached to the common axle of the 
wheel and spiral ; » a loose index under the 
| index m, which the latter carries forward by 
} means of a projecting pin near the extre- 
mity; 0 a tube passing under the cistern a, 
which, entering the bottom, proceeds upwards 
within the vessel ¢ till its open extremity is 
above the level of the water in a neck of the 
vessel ¢; the other end of the tube o is six 
feet above the outer wall of the Observatory, 
where it is capped by a vane p; at the top 
of the tube o three brass rods are joined, 
which carry a small tube in which a pin within 
the top piece q rests or turns ; the tube 0 is 
double at the top, containing between the 
tubes a quantity of mercury to the level r, 
the continuation of the cylindrical body of 
the vane enters the mercury, and a double portion s acts as an outer cover to the mer- 
cury cistern ; tis an aperture, 2 inches square. When the wind blows, this aperture is 
presented to it, the wind then presses on the column of air within the tube o (being 
prevented from escaping under the vane by the mercury), and ultimately on the top 
