1843.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



£53 



Every day at noon all these papers were sent by post to the central station, 

 and immediately on their arrival, the papers of the different stations were 

 compared, and their observations laid down on paper, so as to give a gra- 

 phical representation to the eye of all the observations, by means of which, 

 they were at once verified and compared with great facility. From the exa- 

 mination of these tide-waves thus laid down, certain characters of the tide- 

 wave peculiar to each locality had been discovered. As in the former obser- 

 vations of the Clyde and the Dee, it had been found in this series, that the 

 form and dimensions of a channel produce important changes in the form of 

 the tide-wave. Where the sea was deep and the shore open and abrupt, the 

 form of the tide-wave was symmetrical, and of the form predicted by La- 

 place, where he says, that in rising and falling, the water covers in equal 

 times equal arcs of a vertical circle. This is the form of the ocean tide- 

 wave ; but, on approaching a shallow shore, and travelling along a shelving 

 coast, the tide-wave undergoes two changes — its summit becomes displaced 

 forwards in time, its horizontal chords become dislocated, and the wave 

 ceases to be symmetrical. This peculiar dislocation and displacement are 

 characteristic of a littoral tide, and in the case of running streams, the cur- 

 rents still further affect the tide-wave, and give to it a peculiar distortion 

 characteristic of fluvial tides. To these were further added the exaggeration 

 and elevation of the tide, by means of narrow channels. All these pheno- 

 mena were fully proved by the present series of observations. The author 

 of this paper also considers it to have been fully established by the observa- 

 tions on the Firth of Forth, that there exists on the eastern coast, satisfac- 

 tory evidence of the presence of a second tide-wave in that part of the 

 German Ocean, and that the southern tide- wave, a day older than the 

 northern tide-wave, sensibly affects the phenomena of that part of the 

 coast. To this he attributes the double tides of the Firth of Forth, the 

 nature of which he fully explained. Regarding these double tides, various 

 theories had been formed — and there were various ways in which such tides 

 might happen, whenever tide-waves arrive by different paths in different times. 

 But this kind of double tide was, in this case, only to be explained by the 

 method he had adopted, and which removed the difficulties in which the 

 subject had formerly been involved. He then proceeded to explain the 

 mode of discussion which had been adopted. It was the semi-diurnal ine- 

 quality, so accurately examined by Mr. Whewell, which enabled us to decide 

 on the ages of two tides. If the two tides which appeared together, pre- 

 sented opposite inequalities both in time and in height, regularly alternating, 

 varying with the moon's declination, disappearing with it, and re-appearing 

 with it, and following it regularly, without regard to other simultaneous 

 changes of a different period, then it became plain that ho other inference 

 could be drawn, than that which he had mentioned ; when, further, he had 

 proceeded to treat these tides as compounded of two successive tides, one 

 due to a transit 12A 24m later thau the other, and had used for this purpose 

 two simple river tides super-imposed at a distance in time corresponding to 

 that at which the northern and southern tides could enter the Firth, he had 

 obtained a close representation of the double tides of the Firth of Forth ; 

 when these two methods of examination ended in the same conclusion, he 

 conceived that it had obtained a very high degree of probability. By means 

 of these observations tide-tables had been formed, which were designed to 

 afford a more accurate means of predicting the local tides of the east coast 

 of Scotland than any we now possessed. 



Dr. Robinson and the President put several questions to Mr. Russell, for 

 the purpose of eliciting the facts more clearly. 



Lord Mountcashel inquired whether Mr. Russell had observed and ac- 

 counted for any of the tidal phenomena which were denominated bores, and 

 described one which he had witnessed in the river Seine, the rapidity of 

 which far outstripped that of the steam-boat in which they were proceeding. 



Mr. Russell said that he had frequently observed this phenomenon, and 

 described the bore of the river Dee, and of the Solway frith. He then 

 briefly accounted for it on the principal of the tidal wave coming with 

 enormous rapidity from deep water, where it was freely propagated into shoal 

 water, where the upper part, retaining its velocity less impaired while the 

 bottom was retarded, it toppled over, at length, breaking in its rapid onward 

 course. 



Captain Larcom observed that the ordnance survey would contain a very 

 full account of the tidal phenomena along the coast of Ireland. Captain 

 Larcom hoped before long to lay before the Association the result of the ob- 

 servations made on the coast of Ireland in the course of the ordnance 

 survey. Gauges were established at different stations, and observations have 

 been made every five minutes during the course of three lunations. The 

 direct object of them was to obtain data for the plane of mean sea level ; 

 but while the observations (which are now in course of reduction) are likely 

 to decide this, they also give much valuable information as to irregularities 

 Uke that just mentioned. He might mention that in Lough Swilly the spring 

 tide high water was eight feet higher than in Lough Foyle. 



Mr. Hawkins read a paper on the Friction of Water on Water, as exem- 

 plified in the well-known experiment of emptying a vessel full of water by- 

 sending a jet of the fluid through it. This friction of the particles of fluid 

 against each other, caused the principal obstruction to the motion of ships 

 through the water ; and he conceived that it would be advantageous to grease 

 the bottoms of ships to diminish the friction. 



On the Form of Ships. 



Mr. Scott Russell read the " Report of the Committee on the Form of 

 Ships." 



The report was voluminous ; it contained the reductions of a large number 

 of experiments, and about 20,000 observations, made on more than 100 ves- 

 sels of different forms ; accurate drawings of all of which, on a large 

 working scale, were laid on the table. It was the hope of the committee 

 that this report might be published, in order to give the public all the benefit 

 which accurate knowledge on this point was likely to convey. He did not, 

 therefore, enter fully into the details of these voluminous results, but would 

 confine himself to a general account of the objects which this committee 

 had in view, the methods of inquiry which they had adopted, and a few of 

 the more general conclusions to which they had been led. These experi- 

 ments had now occupied the attention of the committee during a period of 

 five or six years, and it afforded him peculiar pleasure to be able to present 

 the concluded investigation to this meeting. It was appropriate to this 

 meeting, inasmuch as Cork was an important sea-port, of increasing pros- 

 perity, whose interests were involved in everything tending to the improve- 

 ment of our mercantile navy: it was. further appropriate, inasmuch as there 

 existed in the vicinity of Cork a class of the fastest sailing vessels in exist- 

 ence — he meant the fleet of yachts — by the successive trials of which many 

 improvements had been made in the form of vessels ; and, indeed, he con- 

 sidered it due to the yacht clubs of this country to say, that much had 

 everywhere been due to their exertions in the improvement of the speed of 

 our ships. He had had the good fortune to find in Cork a gentleman who, 

 in the recesses of his own study, had been carrying on, for many years, 

 valuable scientific investigations on this subject, who had submitted his 

 views to experiment with great success, but had long felt the want of just 

 such a series of researches as he had this day the pleasure of laying on the 

 table. The beautiful models by which the report was illustrated, had been 

 constructed by Dr. Phipps, to whom he had thus alluded; and in Mr. 

 Beamish, also a native of this place, he had found another scientific and suc- 

 cessful investigator in the same field of inquiry. On this account he should 

 enter more fully into this subject, as one in which Cork was especially inte- 

 rested. It had long been the reproach of science, that so little had been 

 done to enable the practical man to proceed with certainty in his attempts 

 to improve the speed of ships. There are some points in which science has 

 done all that can be desired. The immersion of a ship, her trim, her centre 

 of buoyancy, her stability, can all be determined, with accuracy, beforehand, 

 and the scientific naval constructor can proceed with certainty upon fixed 

 principles. It is otherwise with the speed and resistance of a ship. In 

 nothing does calculation more completely fail them than in the attempt to 

 determine beforehand the speed of a ship constructed on given lines, or to 

 show how a form may be so altered as to render it faster than before. To 

 calculate the resistance opposed by the water to the passage of a ship 

 through it, and to find that form which, at a given velocity, will pass through 

 the water with least resistance, and, of course, with the smallest expenditure 

 of power — such was the problem hitherto the least solved, and always one of 

 the most important, which these experiments were intended to investigate. 

 There were also two phases in which this problem presented itself, the scien- 

 tific and the practical view of the subject. There were, therefore, two 

 classes of experiments — one designed to advance our knowledge of the 

 laws of hydrodynamics which govern the phenomena of resistance of fluids, 

 and the other, the experiments serving as a basis to the operations of the 

 practical construction of ships — the E.vperimenta lucifera and the Evperi- 

 menta fructifera of Lord Bacon. To the latter class, he would confine the 

 remarks of to-day, as belonging more especially to section G, the former 

 having been discussed in section A. Many experiments had formerly been 

 made on this subject, but we had, at that time, so imperfect a system of 

 hydrodynamics, that the conclusions drawn from them could not be relied on 

 with confidence by the practical man. The Academy of Sciences had made 

 a series of such experiments at a large expense defrayed by the French 

 government. Colonel Beaufoy, in our own country, had made an important 

 series of such experiments, at an expense of £30,000, but these were of 

 comparatively little value, for the same reason, viz., that the forms did not 

 comprehend such forms as were actually required for the purposes of naval 

 construction, and because the state of science was not such as to enable us, 

 from the resistance of one form, to deduce with certainty that of another. 

 For the purpose of giving practical value to the present series, experiments 

 had been made on many different scales of magnitude, some in narrow chan- 

 nels, others in large canals, and finally on the open sea. Some were made 

 on models 3 ft. in length, others of 10 ft., some on vessels 25 ft. long, 75 ft. 

 long, and some on vessels 200 ft. long, and nearly 2000 tons capacity. Thus 

 it was trusted that the scale of the experiments was such as to give confidence 

 in the results. Next, as regards the forms of vessels made the subject of ex- 

 periment, these were similar to those required for the practical purposes of 

 construction. One class consisted of such forms as were required for steam 

 navigation. Plans of steam ships of the best construction and others of 

 worse forms, were accurately laid down on the same scale, in the same way, 

 and with the same accuracy of proportion as if they had been for actual ser- 

 vice, and along with these were some of new forms. A given form having 

 been found to be a good one, was then varied by lengthening, first in 

 or.e ma'inpr then in another, to discover the best mode of improving a given 

 goo<! form. In sailing vessels, some of the celebrated Chapman's best forms 

 were taken, and treated in a similar manner, and along with them were com- 



48 



