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 Avorks. 



It is jiroper, however, to observe, that there may be some objection to refer- 

 rinsi' 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 

 mav, from supposing them to have continuity of action, be perhaps regarded as 

 similar to a statical pressure, rather than to the impact of a hai-d body.* The near 

 coincidence, or indeed almost perfect agreement of the results of the experiments 

 made with different instruments, goes far to shew that the Avaves 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 wei-e almost identical. 

 Now, the same force, supposing the Avaves 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 Avhich that force was expended or developed ; so that with 

 the same force of impact, the indication of a weak spring Avould 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 bod}'. 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 Avhen 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 

 Beitli's Dam, a reservoir situated upon the higli grounds near Cartsdylie, 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 melanclioly loss of no fewer than 41 lives. This continuous tlow of water carried 

 away many houses ; and, among other instances of its power, it is recorded that a " mass of rock about 

 IG tons weight was borne along by the torrent to a distance of 30 or -10 yards." This case, then, which 

 almost equals the records of the fury of the sea, shews the effects which continuous action may produce. 



