March 17, 1905.] 



SCIENCE. 



435 



the section the velocity is diminished, the air 

 must flow faster in some other portion. This 

 theory seems to explain satisfactorily the in- 

 creased velocity between 300 and 700 ms. at 

 night. The retardation of the air between 

 200 and 700 meters during the day, due to 

 ascending currents, results in an increased 

 velocity near the ground, and, as this is not 

 sufficient compensation, also in the section of 

 air between 1,000 and 2,000 meters. Hence, 

 at the latter height, the velocity has a maxi- 

 mum by day and a minimum by night, as is 

 the case at the ground. 



Vertical Gradients of Temperature, Humid- 

 ity and Wind Velocity. — At night the tem- 

 perature rises with increase of altitude up to 

 about 500 meters, and not until a height of 

 over 1,000 meters is reached is the tempera- 

 ture in the free air as low as at the ground. 

 During the day the temperature decreases 

 with altitude nearly at the adiabatic rate for 

 dry air up to 500 meters. Above that height 

 the rate decreases, probably owing to frequent 

 inverted gradients and to cloud formation. 

 Between 500 and 1,500 meters the temperature 

 decreases more rapidly by night than by day. 

 The decrease is most rapid in summer and 

 least in winter. During the day the rate of 

 decrease diminishes to 2,000 meters, and then 

 increases again. From to 500 meters the 

 rate is at a maximum by day and a minimum 

 by night, but between 1,000 and 1,500 meters 

 this condition is reversed, owing to the inver- 

 sion of the diurnal period. An important 

 point, noted on page 50, concerns the mean 

 vertical temperature gradient, about which 

 much has been written. Gradients which are 

 the mean of two opposing conditions may not 

 occur at all. The most frequent gradients 

 which actually occur are (I.) an increase of 

 temperature with increase of altitude, between 

 -f 0°.l and 4-l°.0 (C.) per 100 meters, and 

 (II.) the adiabatic gradient, 1°.0 (C.) per 100 

 meters. Some gradients exceeding the adia- 

 batic rate have been observed, chiefly between 

 9 A.M. and 3. p.m. On the average, the rela- 

 tive humidity increases during the day up to 

 about 1,000 meters, and then decreases to 

 about 2,500 meters. During the night the 

 relative humidity diminishes rapidly up to a 



height of 500 meters, and then more slowly, 

 to a height of about 2,500 meters. Above 

 2,500 meters the relative humidity increases 

 slowly again. There is a very rapid increase 

 of wind velocity at night to a maximum at 

 500 meters, a slight decrease between 500 and 

 1,000 meters, and then an increase becoming 

 more rapid with increasing height. There is 

 a relatively rapid increase of wind velocity by 

 day from the ground to 500 meters; a slower 

 decrease from 500 to 1,500 meters, and almost 

 no change from 1,500 to 2,000 meters. 



R. DeC. Ward. 



MEETING OF THE BRITISH ASSOCIATION 

 IN SOUTH AFRICA. 



The British Association will hold its meet- 

 ing this year in South Africa. In these ex- 

 ceptional circumstances, the general officers of 

 the association requested the council to ap- 

 point a strong committee to cooperate with 

 them in carrying out the necessary arrange- 

 ments. This ' South African Committee ' has 

 held frequent sittings ; and its work is so far 

 advanced that the London Times is now able 

 to make the following announcements: 



Although the annual circular and program 

 have not yet been issued, pending the receipt 

 of information from South Africa, many mem- 

 bers have already intimated their intention of 

 being present at the meeting. The ' official 

 party ' of guests invited by the central execu- 

 tive committee at Cape Town, and nominated 

 in the first instance by the council of the 

 association, numbers upwards of 150 persons, 

 comprising members of the council, past and 

 present general officers and sectional presi- 

 dents, the present sectional officers, and a cer- 

 tain proportion of the leading members of each 

 section. To this list has yet to be added, on 

 the nomination of the organizing committee, 

 the names of representative foreign and 

 colonial men of science, the total number of 

 the official party being restricted to two hun- 

 dred, including the local officials. It is hoped, 

 however, that many other members of the asso- 

 ciation will also attend the meeting. 



The presidents-elect of the various sections 

 are as follows : 



