B. TERRESTRIAL PHYSICS AND METEOROLOGY. 103 



volved in the method are such as have been previously fre- 

 quently applied. Dr. Prestel having stationed himself at one 

 end of a short line of telegraph, and being in convenient com- 

 munication with his student, Mr. Meyer, at the other end of 

 the line, they observed with the sextant the apparent alti- 

 tude and azimuth of the lower surfaces of such clouds as 

 they from time to time agreed upon. The observations were, 

 of course, taken at the same moment of time, and, from a 

 number of determinations made during the winter and sprino* 

 months in the neighborhood of the city of Emden, they found 

 that the heights of the lower surfaces of the cumulous clouds 

 vary from 5000 to 20,000 feet, being lowest when the tem- 

 perature is low, and highest when the temperature is high. 

 Prestel hopes to continue the observations to a sufficient ex- 

 tent to enable him to determine the averao;e heig-ht of the 

 low^er surflices of the clouds at various hours during the day. 

 Zeitsdtrlft der Oest. Gesell.fur3Iet.^ 182. 



ox THE SEMIDIURNAL VARIATION OF THE BAROMETER. 



Broun, the director of the observatorv at Makerstoun, 

 has studied the effect of the sun on the daily change in tlie 

 barometer, as shown by observations made in India. He 

 states that in the pleasant season in Malabar, the diurnal os- 

 cillation of the barometer is very large. The air at 6000 feet 

 above the sea is, during many days, of perfect tranquillity. 

 Small clouds form and dissipate in the valleys after rising, 

 and without moving to the one side or tlie other. In April, 

 when the monsoons begin, the clouds begin to form in great 

 masses on the coast of Malabar. They increase gradually 

 from morning till the afternoon, rising to a height of 4000 or 

 5000 feet. They neither advance nor increase for some hours, 

 and gradually disappear toward evening. The tranquillity 

 of the air is so great that Broun has, upon the mountain, ex- 

 amined the particles of the clouds with the microscope of the 

 theodolite as they slowly moved in front of the objective. 

 The shell of warm air at the surface of tlie earth ought to 

 rise until it loses its excessive temperature, and should be 

 replaced by the shell of air immediately in the neighborhood, 

 which should rise in its turn ; but there is no ascending cur- 

 rent of air of this kind, and the hypothesis which requires 

 the clouds, as well as the diurnal variation of the barometer, 



