Vanes and Anemometer. 



lxi 



tion of the wind could be estimated from it during the day only. On November 13, 

 1844, a larger vane was formed of four large feathers from a turkey's tail, this vane 

 was mounted on a long and light fir-rod, which passed through the roof of the Obser- 

 vatory, and had an index attached to its lower extremity, which indicated the direc- 

 tion of the wind on a compass fixed to the ceiling of the Observatory. This vane 

 indicated the direction of the lightest winds, and the direction of the wind was gene- 

 rally taken from it after November 13, 1844. The direction of the wind is indi- 

 cated in this volume by the number of the point of the compass, reckoning N = 0, 

 E = 8, S = 16, W = 24. 



101. The anemometer, the invention of Mr R. A die, 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 : 

 a is a cistern containing water to the level 6, 

 c being a turn-cock for letting the water off 

 to the exact level, and d a glass-gauge to shew 

 when the water becomes too low, from eva- 

 poration or otherwise ; an inverted vessel e 

 is suspended in the water by a cord passing 

 over the wheel/, whose axle rests on friction- 

 rollers at g and h ; i is a spiral, which has a 

 cord wrapped onit carrying a weight Jc, which 

 balances the vessel e ; I is a dial, graduated 

 on the face near the circumference ; m an in- 

 dex, attached to the common axle of the 

 wheel and spiral ; n a loose index under the 

 index m, which the latter carries forward by 

 means of a projecting pin near the extre- 

 mity ; o a tube passing under the cistern a, 

 which, entering the bottom, proceeds upwards 

 within the vessel e till its open extremity is 

 above the level of the water in a neck of the 

 vessel e ; 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 o is 

 double at the top, containing between the 

 tubes a quantity of mercury to the level r, 

 the continuation of the cylindrical body of 

 MAG. AND MET. OBS., 1844. q 



