150 



On the Diurnal Barometric Maxima. 



[May 3, 



A solid formed of such shells and the action of outer shells upon 

 inner ones, or vice versa. 



40. Case of a solid shell of small finite thickness. 



41. Of statical distribution of electricity on a conductor as pro- 

 duced by variation of magnetic field. 



42. Of non-self-inductive systems. 



II. " On the Relations of the Diurnal Barometric Maxima to 

 certain critical Conditions of Temperature, Cloud, and 

 Rainfall." By Henry F. Blanford, F.R.S. Received 

 March 30, 1888. 



(Abstract.) 



The author refers to an observation of Lamont's that the diurnal 

 barometric variation appears to be compounded of two distinct ele- 

 ments, viz., a wave of diurnal period, which is very variable in dif- 

 ferent places, and which appears to depend on the horizontal and 

 vertical movements of the atmosphere and changes in the distribu- 

 tion of its mass, and a semi-diurnal element which is remarkably 

 constant and seems to depend more immediately on the action of the 

 sun. Then, referring to the theory of the semi-diurnal variation, 

 originally put forward by Espy, and subsequently by Davies and 

 Kreil, the author points out that the morning maximum of pressure 

 approximately coincides with the instant when the temperature is 

 rising most rapidly. This is almost exactly true at Prague, Yarkand, 

 both in winter and summer, and in the winter months at Melbourne. 

 At the tropical stations, Bombay, Calcutta, and Batavia, and at Mel- 

 bourne in the summer, the barometric maximum follows the instant 

 of most rapid heating by a shorter or longer interval ; and the author 

 remarks that this may probably be attributed to the action of convec- 

 tion, which must accelerate the time of most rapid heating near the 

 ground surface ; while the barometric effect, if real, must be deter- 

 mined by the condition of the atmosphere up to a great height. With 

 reference to Lamont's demonstration of the failure of Espy's theory, 

 a condition is pointed out which alters the data of the problem, viz., 

 the resistance that must be offered to the passage of the pressure- 

 wave through the extremely cold and highly attenuated atmospheric 

 strata, whose existence is proved by the phenomena of luminous 

 meteors. 



With respect to the evening maximum of pressure, it is pointed out 

 that very generally, and especially in India, and also at Melbourne, 

 there is a strongly-marked minimum in the diurnal variation of cloud 

 between sunset and midnight, which, on an average, as at Allahabad 



