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.
