B. TERRESTRIAL PHYSICS AND METEOROLOGY. 69 



OX THE TEMPERATURE OF THE MEDITERRANEAN SEA NEAR 



THE COAST OF ALGERIA. 



Messrs. Grad and Hagenmiiller, in 1872, made a series of 

 observations on the temperature of the water, on the occa- 

 sion of a voyage along the shores of Algeria, and have con- 

 tinued them at three fixed stations since that year. The 

 mean temperature of the surface through the year is found 

 to vary from 18.3 Centigrade at Algiers, up to 19.5 at Oran ; 

 the extremes between winter and summer being 11 and 18 

 respectively. Observations were made at difterent depths, 

 down to four meters, at the fixed stations ; and by compari- 

 son of the Algerine with the Adriatic measurements, it would 

 seem that the isothermal lines on the surface of the Mediter- 

 ranean bend toward the mouth of the Adriatic Sea, w^liere 

 the temperature is higher during the winter and spring time. 

 6 JB, LXXXL, 292. 



UNDERGROUND TEMPERATURES. 



In some notes on the cjeneral facts relatino; to undero^round 

 temperature, Mr. Schott states that the earth's solid crust 

 being hotter than the mean temperature of the lower stratum 

 of the atmosphere resting on its surface, heat is constantly 

 and very slowly passing outward, and strata of equal depth 

 w^ould have very nearly uniform temperatures but for the 

 influence of the irregular daily and annual variations of the 

 atmospheric temperature received by conduction. The depth 

 of the stratum of the so-called invariable temperature (viz., 

 where the changes escape ordinary observation, or are less 

 than 0.01 Centigrade) is found about six meters below the sur- 

 face of the ground in the tropics, and about thirty meters be- 

 low the surface in the middle latitudes. The depths at which 

 the daily variations become imperceptible are, for these two 

 regions of the globe, respectively 0.3 and 1.3 meters. These 

 numbers, however, depend greatly upon the kind of soil or 

 rock forming the surface, and differ considerably according to 

 the porosity of the loose soil. The mean temperature of the 

 earth's crust increases wdth increasing depth, and for moderate 

 depths frhe increase is nearly uniform at the rate of 1 Centi- 

 grade for 28 meters. For greater depths, the descent neces- 

 sary to produce an increase of 1 of temperature is greater 



