Nov. 28, 1859.] LIVINGSTONE'S CENTRAL AFRICAN EXPEDITION. 19 



In the case of the Irish and English survey, as he hefore remarked, they 

 were fourteen days intensely occupied in obtaining simultaneous observations, 

 and he believed it resulted only from their very perfect calculations that they 

 were enabled so truly to dh'ect their telescopes and eventually succeed. 



Mr. T. Maclear, f.r.g.s.. Astronomer Eoyal at the Cape, was convinced 

 from experiments which had been made at the Cape of Good Hope, that with 

 a five or six inch screen, from 120 to 200 miles a glass might be seen as a star 

 of the fourth or fifth magnitude, through a small telescope. They had very 

 successfully employed signals at a distance of 25 miles. 



Mr. GtALTon remarked, in answer to Sir E. Belcher, that the difficulty of 

 aim was altogether independent of the distance, and that, with his own hand- 

 instrument, the horizon could be swept, and a correspondent sought out, with 

 the utmost facility, as he himself had continual occasion of experiencing. 

 But, on the other hand, without some optical contrivance for knowing accu- 

 rately where the flash was being sent, it was extremely improbable that the 

 small cone of rays which proceeded from the mirror should be thrown in the 

 desired direction, and still more so, that it should be made to cover the distant 

 station for a sufficient length of time to be properly visible. 



The second Paper read was :— 



2. Latest ^ccow/zis/rom Dr. Livingstone, f.r.g.s., of the Central African 



Expedition. 



The numerous papers received from Dr. Livingstone refer to tv^o 

 main points : the one the navigability of the Zambesi, and the other 

 the capabilities of the valley of its affluent, the Shire, and those of 

 the Shirwa lake, which adjoins it. 



The Zambesi has been examined five times over from between 

 Tete to the sea, and Dr. Livingstone's conclusion is, firstly, that a 

 navigable entrance has been determined by Captain Berkeley, of 

 H.M.S. Lynx, up the Luabo, and by himself up the Kongone. Secondly, 

 that a large vessel could be taken up to Tete at any time between 

 January and April. (This is the unhealthy time of the year ; but 

 the Zambesi fever has hitherto appeared a far less formidable illness 

 than was feared.) Thirdly, that in a season of unusual drought there 

 were found to be only three crossings, from one deep channel to 

 another, over which his little steamer had to be dragged. These 

 were from 24 to 18 inches deep, and from 100 to 150 feet long. 

 The force of the current of the river averages 2i knots, but never 

 exceeds 4 ; and Dr. Livingstone considers that a vessel, literally 

 drawing no more than l-j feet water, could ply at all seasons for the 

 first 300 miles of the Zambesi. 



Above Tete the case is different. The long rapids of Kebra-brasa 

 commence 30 miles from that town. They were visited by Dr. 

 Livingstone when the river was still at its lowest, and he describes 

 the appearance of the first part of them as follows : — The river was 



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