384 SCIENTIFIC RECORD FOR 1882. 



Among recent climatological changes perhaps none are more interest- 

 ing than the conclusion of Dr. Lenz with reference to the African Sa- 

 hara, which region Dr. Lenz explored in 1880. The northern portion of 

 the Sahara is a plateau, 1,200 feet high, consisting of horizontal Devonian 

 strata. South of this are depressions 400 feet above sea-level, but the 

 remainder of the desert is 800 or 900 feet high. Evidences were fre- 

 quently seen of the ancient fertility and population of the desert. Dur- 

 ing his forty-three days' travel through the Sahara, Dr. Lenz observed 

 that the temperature was not excessive; it usually was from 34° to 

 30° C, and only in the Igidi region it reached 45°. The wind blew 

 mostly from northwest, and it was only south of Taudeni that the trav- 

 eler experienced the hot south winds (edrash) of the desert. As to the 

 theory of northeastern trade-winds being the cause of the formation 

 of the desert. Dr. Lenz remarks that he never observed such a wind, 

 nor did his men; it must be stopped by the hilly tracts of the north. 

 Another imjjortaut remark of Dr. Lenz is what he makes with respect 

 to the frequent description of the Sahara as a sea-bed. Of course it was 

 under the sea, but during the Devonian, Cretaceous, and Tertiary periods. 

 As to the sand which covers it now, it has nothing to do with the sea; 

 it is the product of destruction of sandstones by atmospheric agencies. 

 Northern Africa was not always a desert, and the causes for its being 

 so now must be sought for, not in geological but meteorological influ- 

 ences. {Nature, XXV, p. 211.) 



Dr. r. Augustin communicates to Sitzungsherichte a paper on the cli- 

 mate of Prague, being a summary of meteorological observations made 

 since 1840, and also a paper on the influence of cloudiness on the diurnal 

 march of temj)erature at that station. The average temperatures are 

 for winter, — 0^.56 C; for spring, 8°.71; for summer, lOo.Ol; for autumn, 

 QO.GO; for the year, 9o.l8. {Nature, xxvi, p. 165.) 



The London Meteorological OfiBce has published a volume of charts 

 on the meteorology of the ocean in the neighborhood of the Cape of Good 

 Hope. These charts, among other things, show by means of Galton's 

 wind rose the j)robability for any particular ])lace and season of a wind 

 from any point of the com])asts. Li coml)ining the wind observations, 

 an attempt has been made to allow for the tendency of the marine ob- 

 servers to overestimate adveise winds. The charts show in an inter- 

 esting manner the intermingling of hot and <,'old water currents in that 

 jjortion of the ocean. {Nature, xxv, p. 140.) 



From seven and a half years' observation at Alexandria, Egypt, the 

 following summary of its climatological features is derived. Atmos- 

 pheric presisure is remarkably steady, the annual range being three- 

 tenths of an inch. During the winter months, northerly and southerly 

 winds are almost equally frequent, but during the summer months 

 northerly. The lowest relative humidity occurs during winter, and the 

 maximum in July; but the average cloudiness is a maximum, namely, 

 0.4 in winter, with a minimum of 0.1 in summer. The minimum tern- 



