i8 Report S.A.A. Advancement of Science. 



into the first, which is, on the whole, over the earth's surface 

 generally, nearly half a day later. This fact is strikingly shewn 

 throughout the summer at Klagenfurt, and is also plain enough at 

 Cordoba. The first maximum, on the other hand, varies largely, 

 averaging 8 a.m. at Klagenfurt, 9 a.m. at Cordoba and Kimberley, 10 

 a.m. at Greenwich and Agustia, 11 a.m. at some places in the west 

 of Europe, and later still on some mountain summits m the north 

 temperate zone. Also as the seasons vary, the time of the morning 

 maximum at any one station will vary. Thus at Kimberley, 

 which is fairly representative, the time of Mi varies from 

 about 8 a.m. at midsummer to nearly 10 a.m. at midwinter, 

 consequently following the sunrise. On considerable mountains, 

 however, the circumstances are exactly opposite : Mi coming 

 later as the sun gets nearer the zenith, so that in some cases 

 Ml almost or quite merges into M2, as, for example, at Great St. 

 Bernard, where the summer oscillation of the barometer resolves itself- 

 into a single wave, with only one maximum and one minimum in the 

 day. Buchan has drawn a very instructive set of curves for Mount 

 Washington, shewing the average diurnal oscillations at four different 

 altitudes during one June. It appears from these that the time of 

 Ml falls about 8 a.m., at 2,900 feet, about 10 a.m. at 4,060 feet, 

 about II a.m. at 5,500 feet, and about noon at 6,300 feet, whereas 

 there is very little difference in the respective times of the other 

 phases. Incidentally also his curves shew that mi gets deeper and 

 m2 shallower with increasing altitude. It is curious that at some 

 places close to sea level in N.W. Europe the diurnal oscillation in 

 summer is almost exactly like that on high peaks, namely, Mi is 

 retarded until it almost, or quite, merges into M2. In the winter, 

 however, the mountain and valley curves are much more nearly like 

 those of the plains in the same latitude. (Fig. 4.) 



According' to Sir John Eliot, the amplitude of the night 

 oscillation in India generally is least from April to July, when days 

 are longest, the temperature and its diurnal range excessive, and the 

 air very dry. He gives also the average times of the different phases 

 as follows : — 



Extra- 

 Tropical Tropical 

 India. India. 



h. m. 



3 27 



9 41 

 16 32 



22 31 



I give in a Table the average monthly ranges of the barometer from 

 one phase to the next at Kimberley, and also the difference between 

 the mean heights of the maxima and minima, together with the amount 

 by which mi falls below the mean (Table 2). 



One very remarkable feature in this Table is that the difference 

 between the mean monthly heights of Mi and M2 is practically 

 constant throughout the year. The differences between the mean 



