B. TERRESTRIAL PHYSICS AND METEOROLOGY. 97 



tides were carried from one to four miles, and doubtless 

 even farther. The hail that fell at one place contained frag- 

 ments of grass, leaves, and particles of sand. This hail gen- 

 erally preceded the rain. Annual Report of the Army Sig- 

 nal-office for 1873, 1046. 



1HE CHANGE OF TEMPEKATUKE WITH ALTITUDE. 



JVIohn, the well-known meteorologist, in an interesting dis- 

 quisition on the distribution of temperature in the neighbor- 

 hood of the city of Christiania, takes occasion to make some 

 general remarks on the change of temperature with the alti- 

 tude, which are of very general value ; as, indeed, is the en- 

 tire essay. This change, as he states, depends upon a num- 

 ber of causes. He says that the diminution of temperature, 

 with the elevation above the earth's surface, is a consequence 

 of the rising and falling of masses of air, and is modified in 

 various ways by local causes, which can equally increase or 

 diminish the local temperature at great or slight altitudes. 

 The transportation of a mass of air from a lower to a higher 

 level, or the reverse, is most easily accomplished when the 

 air is in rapid motion along the surface of the earth, whose 

 inequalities it is forced to follow : in other words, the ascend- 

 ing and descending movements of the air accompany the 

 strong winds. The diminution of temperature with the alti- 

 tude, so far as it depends upon ascending or descending cur- 

 rents, is most easily brought about when winds of consider- 

 able strength blow. In very quiet air the strata of the at- 

 mosphere can, possibly, arrange themselves in a manner that 

 does not always correspond to their resj)ective temperatures 

 and density. The most rapid diminution of temperature with 

 altitude, as well as the greatest precipitation of rain, occurs 

 with winds that are stronger than the normal winds. The 

 rate of diminution increases when the air is very dry. In these 

 cases the radiation of heat is in general stronger, and is great- 

 est at the highest level, where the air is thinner, and the mass 

 of aqueous vapor smaller. The rate of diminution of tem- 

 perature diminishes, or even is turned into an increase, with 

 the altitude, in the colder portion of the year, under the fol- 

 lowing circumstances: If the temperature sink below the 

 normal, and the pressure of the air in the interior of the con- 

 tinent rise higher than on the coast, there follows a cold pe- 



E 



