106 BULLETIN OF THE 



Mr. L. D. Gale read a paper 



ON THE GEOLOGY OP THE LIGNITE FORMATION, AND ON A HITHERTO 

 UNDESCRIBED DEPOSIT DISCOVERED IN 1834 IN NEW YORK BAY. 



Mr. E. S. HoLDEN read a memoir 



ON SIR WILLIAM HERSCHEL'S OBSERVATIONS OF THE SATELLITES- 

 OP URANUS. 



(^See the Appendix to this Bulletin.) 

 Mr. J. B. HiLGARD explained the construction of 



A NEW APPARATUS FOR THE INVESTIGATION OP PERSONAL ERROR 

 IN ASTRONOMICAL TRANSIT OBSERVATIONS. 



72d Meeting. June 20, 18*74. 



Yice-President W. B. Taylor in the Chair. 

 Mr. Wm. Ferrel made a communication 



ON THE LAW CONNECTING THE VELOCITY AND DIRECTION OP THE WIND 

 WITH THE BAROMETRIC GRADIENT. 



(abstract.) 

 Let ^=the barometric gradient in the direction in which it is 

 the steepest, estimated by the amount of change in 

 the mercurial column in the distance of one hundred 

 miles ; 

 'U:=:the velocity of the wind per hour; 

 r- = the radius of curvature of the isobar or line of equal • 



barometric pressure ; 

 i = the inclination of the direction of the wind to the isobar 



on the side of lowest pressure ; 

 n = the earth's hourly angular velocity of rotation in terms 



of the radius ; 

 I =the latitude of the place. 

 The following equation then expresses very nearly the rela- 

 tion in all cases between the barometric gradient and the 

 velocity of the wind : — 



^ (2 n sin I -j- u) V sec i _ (0.524 sin I - \- u) v sec i 



~ 8300^0 ~ 8300000 



in which 



V cos i 



u = 



