28 
THEIR PECULIAR CONSTRUCTION. 
To aid this, there was another plan, by means of 
which the rudder could be elongated vertically in a 
“ seaway,” to assist in the steerage when the after part 
should be lifted by a sea, so that otherwise the rudder 
would be out of water ; or, in navigating the river 
among shoals and sand-banks when the sliding keels were 
up, this rudder tail,” by being raised to a horizontal 
position, would add materially to the power of the 
rudder. 
To secure the vessels as much as possible against the 
consequences of striking on a rock, they were divided 
into compartments by strong iron partitions. In the 
larger vessels there were four of these, making five 
water-tight divisions; any one of which might have 
been filled with water, without its communicating with 
the others ; thereby very much lessening the chance of 
sinking. 
These however, had the very great disadvantage of 
cutting off the free circulation of air throughout the 
vessels. To remedy this defect, Dr. Reid devised a 
system of ventilation by means of fanners, worked by 
the engine when in action, by the current when lying in 
the river, or by hand if necessary ; air was thus to be 
diffused through tubes to every part of the vessels. As 
however, the atmosphere on the coast of Afi’ica, and 
especially in the River Niger, was supposed to be charged 
with deleterious gases, the air before transmission to 
“between decks,” was made to pass through a large 
iron chest, placed on deck, and capable of containing 
