METEOROLOGY. 971 



"The, altitudes have been kept clown purposely, because half of the whole amount 

 of vapor in tlie air is below us at a height of 1,800 meters (less than 6,000 ft.), and 

 it is but fair to assume that the clouds of most importance to us in forecasting are 

 those formed below 2,000 meters. Above 8,000 meters there is practically no water 

 vapor. Most of our clouds are formed under the second heading (mixture), where 

 condensation results from the mixing of two imperfectly saturated currents. Where 

 the mixing is not thorough, but confined to the edges, we have billow clouds; but 

 while mixture is the most common cause of cloud formation, the cloud thus formed 

 is not apt to give heavy rain. Clouds formed under the third heading (ascension), 

 on the contrary, do give heavy rains. Here the cooling is by adiabatic expansion, 

 and the ideal type of this formation is the cloud of the early afternoon in the tropics, 

 with its torrential rain. Under the fourth heading (electrical) the cloud may keep 

 adding to itself because of a very high surface electrification, or a cloud may be in 

 such a critical condition that, as said above, the slightest jar suffices to produce 

 great change. It is conceivable that a cloud-burst may be a sudden change of con- 

 dition. . . . 



"In order to get at the cloud's true meaning we must, in addition to equipping 

 our observers with nephoscope and cloud atlas, have systematic measurements of 

 the cloud height. This is now done at Blue Hill, Upsala, Storlein, and Berlin by 

 means of theodolites and double observing stations. A more direct way, and one 

 which we think is entirely practicable, is to send apparatus up into cloudland by 

 means of kites. This would give us the conditions prevailing at different cloud 

 levels, and the records would not be momentary." 



The use of the spectroscope and electrometer in studying clouds is 

 suggested. It is claimed that by means of a sensitive quadrant elec- 

 trometer the author has been able to '' tell of the approach of the cloud 

 while yet far off and by the changes in the potential to roughly map 

 out the sky." 



Studies of the upper air,^ A. L. Eotch {Boston Commonwealth, 

 1895, Apr. 6, pp. 8, pi. 1). — The composition of the air brought down 

 from the highest levels has been shown to be identical with that at the 

 earth's surface. The pressure is reduced one half for each 3^ miles of 

 ascent theoretically. The temperature toward the limit of the atmos- 

 phere must be far below any temperature ever observed at the earth's 

 surface. The history of observations on the upper air by means of 

 balloon ascensions (29,000 ft.), by balloons without aeronauts (over 10 

 miles), and from the summit of mountains (23,000 ft.) is reviewed. 



Measures of the highest clouds (9 miles) have been made trigonomet- 

 rically at Blue Hill, Massachusetts, and also in Sweden. 



"A knowledge of the movement of high atmospheric layers is of great 

 importance for the theory of the general circulation of the atmosphere, 

 and practically for our weather forecasts, since the forces which develop 

 storms have their origin and sphere of action within two or three miles 

 of the earth." Continuous observations of all the elements in the higher 

 atmosphere can only be made on mountains, though the conditions 

 there can only approximate those in the free air. The discussions of 

 observations at such high stations have contributed largely to the rapid 

 progress of meteorology. The first summit station of any importance 



• Read before the Boston Scientific Society, March 26, 1895. 

 18055— No. 11 3 



