130 SEVENTH REPORT—1837. 
quantities of steam in the boilers, the sizes of the valves, and the loads 
of the engines; at least in the early part of the working stroke. The 
termination of the return-stroke well exhibited the benefit of eapansive 
working. The duty per bushel of coal consumed was shown to be 
from 73 to 86 millions of pounds, lifted one foot high by the consumption 
of each bushel of coal; and from 870 to 1085 tons lifted one foot 
high for one farthing of expense. ‘Tabular statements of the various 
elements employed, and diagrams illustrative of the conditions of the 
engines examined, were also exhibited. 
The communication of Mr. Henwood gave rise to a lengthened 
discussion on the duty of the Cornish engines; and Mr. Henwood 
explained his reasons for thinking that 125 or 120 millions was too 
high for an average duty. The trial which gave 125 millions was of 
too short a duration, not more than 24 hours; and no reliance can be 
placed on short trials, since there may be a considerable reservoir of 
heat worked out; also the engine may be in a much better condition 
than can usually be maintained. Mr. Henwood considered that the 
best duty was obtained from engines having 10 feet stroke in the cy- 
linder and 7 feet in the working barrel, and making from about 5 to 7 
strokes in the minute ; also that the single-acting do more duty than 
than the double-acting engines. 
On the Mechanism of Waves, in relation to the Improvement of Steam 
Navigation. ByJoun Scott Russert, P.RS.E. 
Mr. Russell had at previous meetings of the British Association given 
an account of his investigations in the resistance of fluids to the motion 
of vessels, and ascertained the law of interference of the wave in 
modifying the nature and amount of that resistance. 
Since the last meeting of the Association, he had extended his ob- 
servations to a variety of the applications of the principles formerly 
developed, to certain objects of practical importance, and, amongst 
others, to the improvement of the navigation of such rivers as the 
Thames and the Clyde, where steam navigation is extensively carried 
on. In these rivers it was found that steam navigation was conducted 
under very great disadvantages, when compared with the open sea, 
Mr. Russell had investigated the causes of these impediments, and he 
had found that in shallow water one great impediment to high velocities 
was the generation of the great wave of translation of the displaced 
fluid: the effect of this great anterior wave was to alter the position 
and increase the anterior displacement and resistance of the fluid. The 
next great impediment to steam navigation consisted in the formation 
of lateral currents on the side of the vessel, which, having the same 
direction with the motion of the paddles, had the effect of diminishing 
the relative difference of the velocity of the paddles and of the fluid, 
and thus diminish the propelling power of the paddles. The third evil 
resulting from the use of steam in shallow rivers arose from the stern- 
wave or posterior surge, by which great injury was done to the banks 
