377 



This paper is illustrated by numerous drawings from injected and 

 recent specimens. 



March 3, 1842. 

 FRANCIS BAILY, Esq., V.P., in the Chair. 



Major-General W. Morison, C.B., and Captain Owen Stanley, 

 R.N., were balloted for, and severally elected into the Society. 



A paper was read, entitled, " On the Diurnal Temperature of the 

 Earth's Surface, and the discussion of a simple Formula for ascer- 

 taining the same." By S. A. Drach, Esq. Communicated by John 

 Lee, Esq., LL.D., F.R.S. 



The author observes, in his introductory remarks, that during a 

 period of twenty-four hours the quantity of calorific rays emitted from 

 the sun, and falling on the exposed atmosphere of the earth, is pro- 

 portional to one day's area as swept by the radius vector divided by 

 the square of that radius ; or is proportional to the true angular mo- 

 tion for that day ; which is equivalent to substituting the declinations 

 resulting from the true longitudes for those deduced from the mean 

 ones at mean noons. On the arrival of the rays at the superior limit 

 of our atmosphere, they undergo refraction, absorption, and difficulty 

 of conduction ; and when arrived at the surface of the earth, they 

 sulFer radiation and reflection ; the absorption alone, at a vertical di- 

 stance, amounting to upwards of one-fourth. The maximum sensible 

 heat, he proceeds to observe, appears to follow the sun in its diurnal 

 revolution, being similar, in this respect, to the point of maximum 

 tidal height of the ocean ; hence he applies the term thermal esta- 

 blishment to the retardation of the effects caused by atmospherical 

 conduction and localities, in the same manner that the term tidal 

 establishment has been employed to denote the local constant by 

 which the astronomical effects on the tides are delayed. 



The tables annexed to the paper assume that the degree of the 

 thermometer is proportional to the cosine of the sun's meridian alti- 

 tude, commencing with that on the day of observation, and ending 

 with the altitude thirty days previously. After explaining the for- 

 mation of these tables, and detailing the conclusions derivable from 

 them, the author gives a sketch of the perturbing causes, such as 

 oceanic evaporation, mountain ranges, and other local influences ; he 

 then enters into a discussion of the mathematical expression for the 

 daily heat ; and he concludes with some observations on the theories 

 of temperature and isothermal lines, as affected by the electrical and 

 magnetical conditions of the earth, dependent on its rotation on its 

 axis. 



