EXPLANATION OF THE PLATES. 489 



The direct resistance, as obtained for the Nile, was estimated according to the 

 rule given by Chapman in his slrcliitectura Navalis, Inman's Translation, Chapter IV., 

 was found equal to the resistance of a plane of sixty-two square feet moving perpen- 

 dicularly through the fluid. This quantity, when examined with power and speed, 

 appears to give results more satisfactory than in taking the area of the midship 

 section ; and we find by taking this quantity in relation to the midship section, and 

 comparing it with the results of steam boats, it in general agreed better with the 

 experiments than taking the whole area of the midship section, and would appear 

 sufficiently near for all practical purposes. In some cases, when the plane of direct 

 resistance was obtained for different boats, as for the Nile, they only varied from 

 124 to '132 of the area of this section. It may, however, be proper to observe, 

 that in any case it can only be an element by which to determine nearly the power 

 required for different steam vessels ; as from the friction and adhesive influence of 

 water, the loss of power by the paddle wheels, &c., it would be impossible, with 

 our present knowledge, to give a correct rule ; and we have no experiment that will 

 shew how the resistance varies in different degrees of velocity, only that it is in a 

 higher power than the square of the velocity when the velocity is great. 

 The following are some of the principal elements of construction : 



Length on the range of deck, 180 feet. 



Breadth, extreme, 33 feet. 



Draught of water, afore, 13 feet; abaft, 14 feet 



Weight of hull, 530 tons. 

 Weight of machinery, water in boilers, coal, &c., as follows : 



Tons. cwt. qrs. Ibs. 



Weight of engine ..... 135 3 1 



Ditto of boilers 65 7 3 13 



Ditto of coal boxes .... 10000 



Ditto of water 44 11 1 14 



Ditto of coal 320 



Total 575 



Weight of mast, rigging, ordnance stores, provisions, &c., 347 tons. 



Total displacement, 1452 tons. 



Area of load water line, 5086 square feet. 



Area of the greatest transverse section, 360 square feet. 



Distance of the centre of gravity of displacement before the middle of the 



length on the water line, taken from the fore part of the stem to the 



after part of the stern post, 3 feet. 



3 Q 



