Nov. II, 1880] 



NA TURE 



39 



maintains, than is sufficient to supply the simple wants of 

 the natives. Coal he saw none, and he does not believe 

 that such a thing exists over the wide area embraced m 

 his route. This may be discouraging, but it is whole- 

 some, and may prove a check to the wild schemes some- 

 times broached by speculators for opening up the African 

 interior. From the Chimboya Mountains to the south- 

 east of Tanganyika Mr. Thomson found numerous stream- 

 lets flowing southwards, doubtless to join the Chambeze, 

 which, after passing through many a lake and levying 

 tribute from a region one million sciuare miles in extent, 

 pours its almost .Amazonian volume, as the Congo, 3000 

 miles below, into the bosom of the broad .Atlantic. The 

 much-debated Lukuga he found, as Air. Hore had found 

 shortly before him, to be a broad and rapid river, flowing 

 westwards from the Tanganyilca Lake to the Lualaba, as 

 the Congo here is called ; and Lake Hikwa he saw was a 

 fine sheet of water with no outlet, lying among the lofty 

 mountains, which stretch away east from Southern Tan- 

 ganyika. What may be the extent and value of the purely 

 geographical observations obtained by Mr. Thomson we 

 have no means of knowing ; doubtless in this respect the 

 expedition suffered in the death of Mr. Johnston, who was 

 a trained geographer. But in other respects, in informa- 

 tion as to the structure of the country, the nature of its 

 products, and the character of its varied peoples, the 

 expedition under Mr. Thomson has been fruitful to a high 

 degree ; altogether it is one of the best pieces of original 

 work which our not too energetic Geographical Society 

 has ever done. Mr. Thomson's well-written and well- 

 read paper was received with enthusiasm by an unusually 

 distinguished audience. We trust to be able very shortly 

 to give details concerning both the geography and geology 

 of the Central Plateau from Mr. Thomson's own hands. 



UNITED STATES WEATHER MAPS, 

 DECEMBER, 1878 



IMPORTANT changes took place this month in the 

 distribution of the earth's atmosphere as compared 

 with what obtained during the previous month, and these 

 were accompanied with at least equally important changes 

 in the geographical distribution of the temperature. 



If a line be drawn from Texas to Newfoundland across 

 the Atlantic, the north of France and Germany, thence 

 curving round to south-eastward through the Black Sea, 

 the Caucasus, India, the East India Islands, and Aus- 

 tralia to the south island of New Zealand, it is found 

 to pass through a broad and extended region where 

 atmospheric pressure \ras throughout considerably below 

 the average of December, and this low pressure was still 

 further deepened at various points along the line. Again, 

 another line passing from Australia through the Philip- 

 pine Islands, Japan, Mantchooria, Behring's Straits, and 

 Alaska, also marks out an extensive region where pressure 

 was uninterruptedly below the mean. 



On the other hand atmospheric pressure was above the 

 average, and generally largely so, over the United States 

 to west of long. 90^, over Greenland, Iceland, Faro, 

 Shetland, and over a large portion of the Old Continent 

 bounded by a line drawn from Lapland round by Lake 

 Balkhash, Canton, Pekin, to at least the upper waters of 

 the Lena. Another area of high pressure extended from 

 Syria, through Egypt and East Africa to the Cape ; and 

 part of a third area of high pressure appeared in the north 

 island of New Zealand. 



As regards North America, the greatest excess of 

 pressure, o"ig6 inch above the average, occurred in the 

 Columbia Valle\-, from which it gradually fell on pro- 

 ceeding eastward to a defect from the average of o' 146 

 inch about Lake Champlain and to northward, rising 

 again to near the average on the north of Nova Scotia. 

 To the north-east and north of this region exceedingly 



high pressures for these regions and the season prevailed, 

 being o'635 inch above the average in the north-west of 

 Iceland, 0500 inch in the south of Greenland, and at the 

 three stations in West Greenland, proceeding northwards, 

 0-445, o'402, and o'j46 inch. 



West Greenland being thus on the west side of the 

 region of high pressure which occupied the northern part 

 of the Atlantic, and on the north-east side of the area of 

 low pressure in the States and Canada, strong southerly 

 winds set in over the country, and the temperature rose 

 at the four Greenland stations proceeding from south to 

 north to l°'i, 8^-8, iz^'i, and I4°'4, above the averages. 

 As the centre of lowest pressure was in the valley of the 

 St. Lawrence about Montreal, strong northerly and 

 westerly winds predominated to southward and westward, 

 and there consequently the temperature was below the 

 average, the deficiency at Chicago and St. Louis being 

 9°-5 ; and winds being easterly and northerly in California, 

 temperature there was also under the average. On the 

 other h.and, in the New England States, the greater part 

 of the Dominion of Canada, a considerable portion of 

 British .America, and in West Greenland, as already 

 stated, temperature was above the average. Pressure 

 was much higher at St. Michael's, .Alaska, than it was to 

 south-westward at St. Paul's, Behring Straits, and in con- 

 nection therewith and with the prevaUing winds, the tem- 

 perature at St. Paul's was 2^-9 below the average, whereas 

 at St. Michael's, where strong southerly winds prevailed, 

 the temperature rose to 12^0 about the normal. Hence 

 whilst the continent of America presented striking con- 

 trasts in the distribution of pressure in December, 1878, 

 it presented still more striking contrasts in the distribu- 

 tion of the temperature. Along Baffin's Bay the excess 

 of the temperature above the normal was 14^ '4, and at 

 Behring Straits i2°'o, but in the south of Lake Michigan 

 it was 9^-4 below it. In this last case the change of tem- 

 perature from November to December was probably 

 unprecedented, the mean for November having been I3°7 

 above the average (Nature, vol. xxii. p. 516), whilst the 

 December temperature was 9°-S below it, the difference 

 being 23°'2 ! 



Turning now to Europe, it is seen that Iceland lay on 

 the east side of the patch of high pressure which over- 

 spread that region, northerly winds consequently pre- 

 vailed, and with them a lowering of the temperature to 

 7"-2 below the average. The contrast this oft'ers to West 

 Greenland is very instructive. In both localities pressure 

 was unusually high, but they occupied different positions, 

 the one on the east and the other on the west of the same 

 area of high pressure, with the inevitable result, of 

 opposite prevailing winds, accompanied in the one case 

 with a temperature i4°-4 above the average, and in the 

 other 7°-2 below it. Hence as regards the temperature at 

 the surface of the earth, it is not the height of the baro- 

 meter which rules, but the situation of the locality with 

 respect to areas of high and low pressure; or to put it 

 more popularly, it is the winds which are chiefly con- 

 cerned in the distribution of the temperature. 



In Europe the area of lowest pressure occupied the 

 southern shores of the North Sea, extending thence, 

 though in a less pronounced form, to south-eastward. 

 Hence over the whole of Western Europe winds were 

 north-easterly, northerly, and in the south-west of Europe 

 westerly; thus everywhere, from the North Cape to the 

 north of Italy, temperature was below the normal, in some 

 cases very greatly so, the deficiency being io''4 m the 

 south of Norway, and i2°-3 in the south of Scotland. 

 This is ^the lowest monthly mean temperature known to 

 have been recorded in Scotland since thermometric 

 observations began to be made. 



On the other hand, to the east of this area of low 

 pressure, winds were southerly, and consequently tempe- 

 ratures were high. In some localities in Russia an excess 

 of about \fo occurred, and even over a large proportion 



