26 MR THOMAS STEVENSON ON THE FORCE OF THE 
served in the ocean; and would thus supply the want which, as already stated, 
all engineers labour under, to a greater or less degree, in designing marine works. 
It is proper, however, to observe, that there may be some objection to refer- 
ring the action of the sea to a statical value. Although the instrument might 
perhaps be made capable of giving a dynamical result, it was considered unneces- 
sary, in these preliminary experiments, to do any thing more than represent 
the maximum pressure registered by the spring, because the effects of the waves 
may, from supposing them to have continuity of action, be perhaps regarded as 
similar to a statical pressure, rather than to the impact of a hard body.* The near 
coincidence, or indeed almest perfect agreement of the results of the experiments 
made with different instruments, goes far to shew that the waves act in very much 
the same manner as a pressure, although both pressure and impact.must obviously 
enter into their effect. In the experiments, begun February 1844, and given at 
the end of the paper, the three instruments had not only different areas of discs, 
but very different powers of springs, and yet the results were almost identical. 
Now, the same force, supposing the waves to act like the impact of a hard body, 
would, in the Marine Dynamometer, assume very different statical values, accord- 
ing to the spaces in which that force was expended or developed; so that with 
the same force of impact, the indication of a weak spring would be less than that 
of a stronger. 
In future experiments it may be interesting, however, to test the springs 
dynamically, by means of the impact of a heavy body dropped from a given 
height upon the plate or disc of the instrument. In some experiments lately made 
in this way, by dropping a cannon-ball upon the disc, it appeared, that, within 
the limits of the experiments, there was for each individual spring a ratio be- 
tween the value registered by the leathern index and the calculated momentum 
of the impinging body. These ratios were, of course, found to vary in springs of 
different power, and to be constant only for springs of the same power. Did the 
waves, therefore, act by a sudden finite impact, like the cannon-ball employed in 
this instance, we could scarcely have found such harmony between the results of 
instruments with different springs, as the experiments alluded to afford. At the 
same time, the result cannot, perhaps, be in strictness considered correct ; but, 
from the elongation of the spring being very small, the results may be regarded 
as practically correct,—the more so when we find so remarkable a coincidence 
of results as that alluded to. 
* With reference to the continuous action of water, I may notice the effects produced by the failure of 
Beith’s Dam, a reservoir situated upon the high grounds near Cartsdyke, immediately east of Greenock. 
This dam had a head of 20 feet of water, and gave way on the night of the 21st November 1835, 
when the water, after breaking down another reservoir below it, rushed through the streets of Carts- 
dyke, causing the melancholy loss of no fewer than 41 lives. This continuous flow of water carried 
away many houses ; and, among other instances of its power, it is recorded that a “ mass of rock about 
16 tons weight was borne along by the torrent toa distance of 30 or40 yards.” This case, then, which 
almost equals the records of the fury of the sea, shews the effects which continuous action may produce. 
