TRANSACTIONS OF THE SECTIONS. 167 



floating islands continually brought down the stream had produced a new district 

 many miles in extent, beneath which flows the current of the river. The slave- 

 traders, thus shut out from direct communication with the field of their enterprise, 

 had, however, discovered a passage to the river beyond the banier, by the Bahr 

 Girafle, which proved therefore to be an arm of the Nile, instead of an independent 

 stream like the Sobat. In leaving Khartum with his flotilla. Sir Samuel resolved 

 to ascend by this newly discovered passage. He entered the lower mouth of the 

 Giraffe on the 17th February, in N. lat. 9° 26'. The water was 19 feet deep, and 

 the current about 3| mUes an hour, with a breadth, from bank to bank, of about 

 GO yards. At that time the river was about five feet below the high-water mark 

 of the flood-season. . The stream was winding, and had a mean course from the 

 south-west. Foiu- small granitic hills formed good land-marks in the boimdless 

 flats within 15 miles of the junction, and fine forests bordered the river for about 

 30 miles, diversified by plains of extremely fertile soil. As the expedition pro- 

 ceeded the woods ceased altogether, and the steamers depended on the supply of 

 fuel stored in the vessels in tow. At a distance of about 180 miles up the Giraffe 

 the di-y land disappeared, and they sailed through a boundless marsh ; the river 

 narrowed, the current diminished, and at length progress was stopped altogether 

 by a dense growth of high grass. This was in lat. 7° 47' 46'', and 272 miles by 

 dead reckoning from the mouth. As the guides assured him that a passage really 

 existed through this to the main Nile, Sir Samuel set 1000 men to work to cut a 

 channel through the obstruction ; and, after thirty-two days' labour, a canal, eight 

 miles long, was made, but only to find the stream beyond too shallow to float his 

 steamers. He compared the marsh-grass to sugar-cane in thickness and tough- 

 ness ; and the tangled confusion of decaying vegetation beneath it, to a depth of 

 five or six feet, resembled a mixtm-e of fishing-nets, ropes, mud, sailors' swabs, 

 sponges, and canes, all compressed together in a firm mass, beneath which the 

 water was from ten to twelve feet deep ; while grass, about nine feet high, covered 

 the surface as far as the eye could reach from the mast-head. In the clear river, 

 beyond the obstruction, dry land appeared on either bank, and forests^ within two 

 miles. Herds of antelopes and buflaloes were on the plains, and the rifles secm'ed 

 a supply of meat, which was much needed. From the point where the vessels 

 grounded. Sir Samuel proceeded, with Lieutenant Baker, in a small rowing-boat, 

 hoping to find deep water further ahead ; but he foimd the river impassable, and 

 concluded that the Girafie was only practicable during the season of flood. The 

 whole flotilla of thirty-four vessels turned back the way they had come ; and as 

 the rainy season had set in, putting an end to further progi-ess, he established the 

 encampment, from which he wrote, at Towfikeeya, near the junction of the Giraffe 

 with the Nile. He intended to remain here till November, and then, with all his 

 force of 2000 men, cut a passage through the obstruction in the main river, on his 

 way to Gondokoro. He spoke cheerfully of his prospects ; his stores were aU 

 safely warehoused, and all his men in fair health. Since his settlement at Tow- 

 fikeeya he had liberated 305 slaves, who were being carried down the river by 

 slave-dealers ; half of them the property of the Turkish Governor of one of the 

 Nile settlements. 



On the Great Movements of the Atmosphere. By Alexander Bttchan. 



The author gave the results of an examination of the mean pressure of the at- 

 mosphere and the prevailing winds over the globe, based on barometrical averages 

 calculated for 516 places, and on the mean direction of the wind calculated for 203 

 places. The broad results were these :— In each hemisphere pressures are highest 

 in winter and lowest in summer. In winter; the highest, and in summer the lowest 

 pressures are over the continents ; and in winter very low pressures prevail in the 

 northern parts of the Atlantic and Pacific Oceans. In Central Asia the summer 

 pressure is 0-900 inch less than in winter. This implies the removal in summer of 

 a stratum of atmosphere from the interior of Asia of about 900 feet in thickness. 

 Towards the regions where pressm-es were high, the winds flow from aU directions, 

 not directly towards the centre, but at angles from about 60 to 80 degrees ; and 

 from areas of high pressure the winds are found to flow out in every direction. 



