30-2 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Sbptembee, 



1)6 considered that, of the several elements employed in the calcu- 

 lation, all but one mif^'ht be deemed accurate. 



Tlie interval of time occupied by the transit of a wave with respect 

 to the position of the sliip, llie ilirection of the ship's motion with 

 relation to tliat of the waves, and the speed of the ship throufh 

 tlie water, may all be recorded as essentially accurate. Tlie 

 element in doul)t is that of tlie average distance from summit to 

 summit of the waves. 'I'his distance, it has been seen, was by a 

 twofold process of observation or comparison accordantly assumed. 

 The value of the judginent derived from rapid compaiison of 

 measures by an eye accustomed to such estimations is, it should 

 be observed, far higher than might be generally considered. The 

 practical military commander or engineer officer is able to make, 

 by mere inspection of the ground before him, remarkably close 

 estimates of spaces and dist^inces. M'hen engaged in the Arctic 

 whale fishery, I was enabled, from habit and comparison of un- 

 measured spaces with known magnitudes, to estimate certain dis- 

 tances with all but perfect accuracy. Thus, as to a circumstance 

 in which we were most deeply interested — tlie near approach of a 

 boat to a whale — I fouml it quite practicable, whenever the pur- 

 suing boat ajiproached within twice or thrice its length (except 

 when the position was near end on) to estimate the distance to 

 less than a yard. Now, the means of comparison by the eye as to 

 the estimation of tlie breadth of the Atlantic waves, was that of 

 the ship's length of 220 feet. ^Vhen the ship was fairly in the 

 miiidle of the depression betwixt two waves it was assumed, with 

 reference to this known measure, that something obviously less, 

 but not greatly so, than the ship's length, was the distance of each 

 of the two waves then contemiilated — giving a total width of about 

 600 feet. But the comparison of the time required by a wave to 

 pass from stem to stern, with the average time of transit of an 

 entire wave, yielded a much better result; and, on much considera- 

 tion of the subject, I am inclined to believe that the estimate is a 

 tolerably close approximation to the truth. It should be observed, 

 too, that as the headway of the ship, in the direction of the course 

 of the wave — being a known quantity — it was favourable to the 

 accuracy of the estimate. For, assuming an error in the width of 

 the Ha\ es to have occurred, say to the amount of one-twelfth of 

 the whole, or 49 feet — the eftect upon the calculated velocity of 

 the wave would have been only about a sixteenth, or 2'16 miles 

 per hour. 



The form and character of these deep-ssa waves became at the 

 same time interesting subjects of observation and consideration. 

 In respect to form, we have perpetual modifications and varieties, 

 from the circumstance of the inequality of operation of the power 

 by which the waves are formed. Were tlie wind perfectly uniform 

 in direction and force, and of sufficient continuance, we might 

 have in wide and deep seas waves of perfectly regular formation. 

 But no such equality in the wind ever exists. It is perpetually 

 changing its direction within certain limits, and its force too, both 

 in the same place and in [iroximate quarters. Innumerable dis- 

 turbing influences are therefore in operation generating the 

 varieties more or less observable in natural sea waves. 



In regard to my own observations of the actual forms of waves, 

 nothing particularly new could be expected from an inquiry of 

 this kind in regard to phenomena falling within the pt'r|ietual 

 observation of seagoing persons; yet, at the ris!< of stating vvliat 

 might be deemed common, 1 will venture to transcribe from my 

 notes made with the phenomena before me, tlie leading charac- 

 teristics which engaged my attention. During the height of the 

 gale (March Gth) they«)'ni of the waves was less regular than after 

 the wind had, for some time, begun to subside. Though in many 

 cases when the sea was highest the succession of the primary 

 waves was perfectly distinct, it was rather difficult to trace an 

 identical ridge fm- more than a quarter to a third of a mile. The 

 grand elevation in such case sometimes extended by a straight 

 ridge, or was sometimes bent as of a crescent form, with the 

 central mass of water liiglier than the rest, and, not unfrequently, 

 with two or three semi-elliptical mounds in diminishing series, on 

 either side of the highest (leak. These princijial waves, too, it 

 should be noted, were not continuously regular, liut had embodied 

 in their general mass many minor, secondary, and inferior waves. 

 Neither did the great waves go very prevalently in long parallel 

 series like those retarded by shallow water on approaching the 

 shore; but every now and then changed into a bent cuneiform crest 

 withbreaking acuminating peaks. On tlie following morning(March 

 T), after a second stormy night, wind S.S.W. (line), we had a 

 heavy and somewhat cross sea (from the change of wind from 

 ^^'.S.W. to S.S.M'). But the alnmst unabated magnitude of the 

 more westerly waves indicated a continuance of the original wind 



at some distance astern of us. The gale had moderated at daj'- 

 light, and the weather became fine; but as the sea still kept high, 

 its undulations became more obvious and easily analysed. At 

 three in the afternoon, when about a third part of the greater 

 undulations averaged about 2t feet from crest to hollow, in height, 

 these higher waves coulil be traced right and left as they approached 

 the ship to the extent of a quarter of a mile on an average, more 

 or less. Traced through their extent the ridge was an irregular 

 roundbacked bill, precipitous often on the leeward side of waters. 

 The undulations, indeed, as to primaiy waves, consisted mainly 

 of these roundbacked masses, broken into or modified by innume- 

 rable secondary and smaller waves within their general body. 

 The time in which these waves passed the ship was now, on an 

 average, about \5 seconds, the ship's speed being increased from 9 

 to 11 knots, and the obliquity of the ship's course to the direction 

 pursued by the waves was 3 points. ()n the 9th, two days after 

 the above condition of the waves— whilst the sea yet ran high — 

 few waves could be traced continuously above 300 or 100 yards in 

 extent along the same ridge. The crests often curled over, but 

 none so as to reach the height of a 30-feet wave, and broke for a 

 wide space, estimated at 50 to 100 yards in continuity. 



Miscrllanenu.s \otes and Sugge.stiuii.i. — The mode adopted in these 

 researches of finding the Iwiylit of wave is, I believe, quite satis- 

 factory, and, observed with care and with relation to numbers or 

 proportion of waves, as accurate as need be. The depression of 

 the horizon in respect to the elevation of the observer is too small 

 to form even a correction. As the horizon from the paddle-box 

 y =z 15 feet, had only a depression of 3' 49", the distance of the 

 visible horizon, as seen from this elevation, would be 4'45 statute 

 miles, and the actual depi-essioii in feet due to the distance of the 

 summit of the wave when the ship was in the midst of the hollow, 

 could only be 0'18 foot or 2'16 inches. Other modes of determin- 

 ing the w idth of a wave — or the extent betwixt summit and summit 

 — much preferable to that described (the only available one I could 

 devise) might easily be adopted where the management of the ship 

 was in the hands of the observer. In steam ships the simplest 

 mode for high seas, perhaps, would be, altering the speed of the 

 ship when going in the direction of the wave or against the wave; 

 the ratios of the times of transit of wave-crests, under different 

 rates of sailing of the ship might yield results very close to the 

 truth. In moderate-sized waves the plan adopted by C apt. Stanley 

 — whose observations 1 met with before this meeting — seem satis- 

 factory. But in calms, or moderate weather after a storm — that 

 is, for the determination of the velocities of less elevated waves — 

 a variety of processes might be available. 



Mr. JoHX Scott Russeli. observed that there were great doubts 

 as to the actual heights of waves. It was now beyond a doubt 

 that we had waves 24 feet, 30 feet, and 43 feet high, and with the 

 swelling ci'est even exceeding 45 feet high. From the obser- 

 vations which he had conducted many years since, he had ventured 

 to draw up a table predicting the velocities of sea waves up to 

 even 1000 feet from trough to crest in length. Although the appa- 

 ratus which he had used did not enable him to experiment on 

 waves which exceeded 16 inches in length, yet from these pigmy 

 vvaves it was most interesting to see how accurately the law was 

 obtained; for in his table the velocity of a wave whose length 

 was 559 feet was set down at 30 or 31 miles per hour. Dr. 

 Scoresby's actually-observed velocity for a wave 559 feet in length 

 was 32 miles and a fraction. 



SHIP BUILDI.NG ON THE WAVE PRINCIPLE. 



The following communication fi-om Mr. Dodgson, of the Ponta 

 de Arc'a Iron Works and Dockyard, Rio de Janeiro, to Mr. John 

 Scott Russell, was read: — 



Sin — ^Ilaving been called upon late in the year 1846 to undertake 

 the management of the above establishment (then lately organised), 

 my attention in the ship-building department was more particularly 

 directed to the scientific and elegant system of construction advo- 

 cated by you, of which I had some information from rejiorts in the 

 Ciril Eiiyiiieer and Ai-cliitcrt's Journal. Not being fortunate enough, 

 however, to obtain any information from England res)iecting the 

 ''wave principle," but convinced in my own mind of the correct- 

 ness of the few leading features which I had thus been enabled to 

 collect, I determined to attempt carrying them out in two small 

 steamers, and two brig schooners (of 240 tons) then about to be 

 laid down (October, 1S47). This I was prevented doing to the 

 full extent on that occasion, by the opposition of the parties for 

 whom these vessels were building, supported by the very decided 



