April 19, 1906] 



NA TURE 



595 



numerous tables containing the data for stations which 

 possess observations extending more or less continuously 

 over fifty years or more. 



In a recent number of the Meteorologische Zeitschrifi 

 (January) Prof. Hofrat Hann has contributed a new deter- 

 mination of the mean temperature of the earth's atmo- 

 sphere. In the second edition of his classical " Lehrbuch 

 der Meteorologie," recently noted in this Journal, he gave 

 us the results of a discussion of the material then avail- 

 able, but the publication of more data by Prof. Mohn 

 dealing with the air temperature in the region of the 

 North Pole renders a slight modification of the mean values 

 necessary. 



Prof. Mohn has just completed a study of the meteor- 

 ological observations made during Nansen's memorable 

 North Polar expedition in 1S93-6, and has been able to 

 make a new determination of the mean temperatures of 

 the in for the parallels of latitude 6o° to 90° north. These 

 new values have enabled Prof. Hann to re-calculate afresh 

 the mean temperature of the whole northern hemisphere, 

 using the results obtained in the investigation of Spitaler 

 for 1 In parallels from o", to 55 N. The value obtained 

 for the mean of the northern hemisphere was finally 

 15°- 1 C. For the southern hemisphere Prof. Hann had 

 previously determined the value to be i3°-6 C, so that the 

 mean value for the whole earth comes out as i4°-35 C. It 

 is interesting to remark that the northern hemisphere 

 appears to be i°5 C. warmer than the southern. Spitaler 

 in 1886 came to a similar conclusion, his figures being : — 

 Northern hemisphere ... ... ... i$°-4 C. 



Southern hemisphere ... ... ... t4°-8 ,, 



Whole earth ... ... ... ... ... i5°-i ,, 



Excess of N. over S. ... ... ... o°-6 ,, 



Prof. Hann points out that the meteorological observ- 

 ations made during the recent Antarctic expeditions will 

 be of special interest in relation to this question, since a 

 new and better determination of the value for the southern 

 hemisphere is rendered possible. 



Attention is directed to the investigation of Prof. Supan, 

 who formed the mean air temperatures into two groups, 

 namely, east and west hemispheres, the dividing lines being 

 20° W. and 160 E. In this case the eastern hemisphere 

 appears to be the warmer, as can be judged from the follow- 

 ing mean temperatures calculated by Prof. Hann : — 



Hemisphere 

 West East 



North Pole to equator ... i4°-6 C. ... i5°-6 C. 



North Pole to 30 N. ... 5°-o 5°-4 ,, 



30 N. to equator 24°-i ,, ... 25°-8 ,, 



Equator to 30 S 23°-i 23°-6 ,, 



Equator to 50 S i9°-6 ,, ... i9°4 ,, 



It is only when more southern latitudes are included in 

 the regions investigated that the resulting values give an 

 excess of temperature for the western hemisphere. 



In the northern hemisphere the land exceeds the water 

 surface, while the opposite is the case in the southern 

 hemisphere. The figures given above for these districts 

 indicate, therefore, that the land has a capacity for raising 

 the mean temperature of the air, the temperature of the 

 northern in excess of the southern hemisphere being i°-5 C. 

 According to General Tilto, there is a greater proportion 

 of land to water in the eastern than in the western hemi- 

 sphere, the values being 



Percent. Perctnt. 

 land water 



Western Hemisphere (8o° N. to 70' S.) ... 17 ... S3 

 Eastern ,, ,, ,, ... 37 ... 63 



From this, therefore, the eastern hemisphere should be 

 warmer than the western. The above figures show that 

 this is actually the case, thus corroborating the deductions 

 made for the relative temperatures of the north and south 

 hemispheres. 



In an article which appeared in these columns in 1904 

 (vol. lxx., p. 177) entitled " A World-wide Barometric 

 See-saw." an account was given of the result- of .1 

 study by Sir Norman Lockyer and myself of baro- 

 metric changes of short period,' which brought to light the 

 existem e of two large regions on the earth's surface, anti- 

 podal to one another, which behaved in an inverse manner 



no. 1903, VOL. 72,~] 



to each other. In this article a chart was given illus- 

 trating the distribution of the different types of pressure 

 variation, and it was pointed out that the further any 

 station was placed from the centres of the two main 

 regions, namely, India and Cordoba, the less the baro- 

 metric variations were like those of these two regions. 



In a recent paper by Dr. Wilhelm Krebs, of Gross- 

 flottbek, entitled " Barometrische Ausgleichsbewegung in 

 der Erdatmosphare " (Das Wellall, Jahrgang 6, Heft 8, 

 p. 1 iS), the distribution of this short-period barometric 

 change is discussed, and the author constructs an isophase 

 chart from some of the data published in the original com- 

 munication from which the above-mentioned article was 

 an abstract. 



The method adopted by Dr. Krebs is to call the Indian 

 (Bombay) barometric change 100 per cent., and determine 

 the percentage of the changes in relation to India at nine- 

 teen other stations distributed over the earth's surface. 

 This procedure is really not valid, because there are two 

 stations, namely, Bombay and Cordoba, which should both 

 be taken as too per cent, each, the one positive and the 

 other negative. Calling Bombay 100 per cent., Dr. Krebs 

 deduces Cordoba as 31 per cent. ! Since the Cordoba 

 pressure change is the inverse of that of Bombay, it is 

 difficult to see how the 31 per cent, is obtained. Further, 

 the chart becomes very misleading, for the isophase lines 

 connect up places which have a totally different short-period 

 barometric variation. Thus, for instance, his 70 per cent, 

 line passes through Norway and Sweden, European Russia, 

 Arabia, the Indian Ocean, and Australia. The pressure 

 changes in the latter three regions are closely similar, but 

 all very different from those existing in the first three 

 regions named. 



As a matter of fact, the chart already referred to as 

 published previously in this Journal was really an isophase 

 map. In it each of the different signs there adopted, 

 namely, +, + ?, — , — ?, &c, represented types of baro- 

 metric changes, the + signs, for instance, representing all 

 places which behaved like India, and therefore represented 

 as 100 per cent, according to Dr. Krebs's method. A more 

 minute differentiation than this seems at present impossible 

 until a much larger number of stations are employed in 

 the survey. William J. S. Lockyer. 



THE MINERAL WEALTH OF ALASKA. 

 ID ECENT developments have shown that Alaska as a 

 mining field stands in the front rank among the 

 possessions of the United States. Its annual gold produc- 

 tion represents a value of some [,6oo,ooo2. It produces 

 silver, copper, and coal in considerable quantities, and its 

 recently discovered tin and petroleum deposits are of great 

 promise. During the past year the investigation of the 

 mineral resources of Alaska has been energetically carried 

 on by the United States Geological Survey under adverse 

 conditions, and the Bulletins (Nos. 259, 250, and 236) 

 recently published by Mr. A. H. Brooks, Mr. G. C. Martin, 

 and Mr. C. W. Wright afford striking evidence of the 

 excellent work that is being done in this direction by 

 officers of the survey. Attention has naturally been directed 

 chiefly to the gold placers. The placers of the Seward 

 Peninsula, a field embracing in area of 20,000 square 

 miles, still hold the first place in gold production in 

 Alaska. Seven distinct types of alluvial gold deposits are 

 met with in Alaska : — 



(1) Creek placers, at the level of small streams. 



(2) Hillside placers, on slopes. 



(3) Bench placers, in ancient stream deposits 50 feet to 

 300 feet above present streams. 



14) Gravel-plain placers, in the coastal plain of Seward 

 Peninsula. 



(5) Sea-beach placers, on shore to which waves have 

 aci ess. 



11.1 Lake-bed placers, in beds of present or ancient lakes. 



(7) River-bar placers, on gravel flats near the beds of 

 large streams. 



The mining of placer gold in Alaska is carried on during 

 June, July, August, and September; and mining operations 

 are rendered difficult not only by the short available season, 

 but also by the lack of fall in the streams, the poor suppl] 



