164 



cliffs of lias and oolite rise to a considerable height, give a 

 highly interesting feature to the geology of the Western Isles. 



Second Meeting — November 4, 1860; 

 J. B. YATES, Esq., in the Chair. 



Eesignations were received from Mr. E. Estill, Mr. A. 

 RiMMER, Mr. A. Waterhouse, and Mr. J. H. Irvine, and 

 accepted. 



The Rev. J. S. Howson, M.A., Principal of the Collegiate 

 Institution, was elected a Member of the Society. 



Reference having been made in the report of the retiring 

 Council to the erection of an Osier's Anemometer at the 

 Liverpool Observatory, Dr. Thomson made some observations 

 respecting that instrument. The following is an abstract of 

 the Secretary's remarks : — 



The Anemometer, as its name implies, measures the pressure 

 of the wind ; the direction is, properly speaking, denoted by 

 the vane — the anemometer is, therefore, more perfect than the 

 vane. The pressure of the wind being got, the velocity can 

 be computed at the instant of observation, for the one is a 

 constant function of the other; the momentary velocity and 

 the momentary pressure being in the ratio of square root. 

 But to obtain a mean pressure and a mean velocity a different 

 construction is needed, for " the mean velocity is not a con- 

 stant function of the mean pressure ; and the total air move- 

 ment is not a constant function of the sum of the pressures.'' 



Whewell's anemometer, an instrument already erected at 

 the Observatory, is constructed to record the space moved 



