260 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[AuGxrsTj 



observations upon such a connected system. For this purpose, llje vessel 

 OD-fat to carry, in addition to a crew sufficient to work her, ten or fifteen 

 men wlio, by themselves (in pairs) or under the direction of petty officers, 

 micht be trusted lo make tide observations for a week or a fortnight at 

 selected points of coast. The surveying vessel ought to be provided with 

 a launch to be employed in carrying these observers to their station, visit- 

 ine them while engaged in their work, or feiching them away when their 

 task at each place is done. P'rom one region to another of the ocean, 

 standard stations ought to be selected, at which tide observations should 

 be continued for a longer lime, and the observations made in each region 

 should be compared wiih those at the standard staiion. The comparison 

 of the observations with each other, as the survey proceeded, would point 

 out the direction in which it was desirable to extend the survey, and the 

 special points to be attended to. We, therefore, recommend that applica- 

 tion be made to the Admiralty that they would appropriate to this service 

 a suitable vessel. 



Mr. Orleear informed the meeting that he had, while at Bombay, con- 

 ducted a regular series of observations on the progress of the tides ; that 

 similar observations had been made in other parts of India, and at Aden 

 at the mouth of the Red Sea ; and that the Geographical .Society had seen 

 the importance of those observations, and had lately turned their attention 

 to them. 



The AsTBONOMF.R-RoYAL inquired at what intervals the observations at 

 Bombay were taken ? 



Mr. Orlebar replied that they were taken by a tide gauge, and were, 

 therefore, continuous. 



The AsTRONOMER-RoYAi. said that frequency of taking the observations 

 •was most essential. Upon analyzing the observations he had lately su- 

 perintended round the Irish coast, the extraordinary fact had been ascer- 

 tained that at some places four tides took place in the day ; and the 

 continuance of the waves of these tides could be distinctly traced to a 

 considerable distance on each side south. 



Mr. Orlebar said that nothing had been done in the way of analysis or 

 reduction of the Bombay observations. 



Dr. Wmewell pointed out several peculiarities of the tides in the East 

 Indies— particularly dwelling on those at Singapore. He also drew 

 attention to the researches of Admiral Liitke on the north coasts of Ame- 

 rica and in the Northern Ocean ; and begged to ask Prof. Struve whether 

 those were not still continued. 



Prof. Strcve replied that the researches of Liitke were still continued, 

 particularly along the shores of the White Sea and various parts of the 

 IiJorthern Ocean ; and he believed he was almost the only navigator who 

 had bestowed a large portion of attention on the determination of co-tidal 

 lines, 



" On English Measures." — The Astronomer Royal stated that it would be 

 interesting to learn that one of the chief objects of their illustrious visitor, 

 Professor Strove, when coming to England, was to make a comparison of 

 the English standards of length with those of Russia. — M. Struve stated 

 that one of the special commands which he had received from his royal 

 master was to make that comparison with minute accuracy. A knowledge 

 of the English standard was of much consequence in Russia, as the Sngenc 

 of that country was exactly equal to seven English feet. — Sir John 

 Hersciiel said, that although England was at this moment without a Par- 

 liament standard of length, yet one would soon be completed, as the com- 

 missioner for that purpose had nearly brought his labours to a close. The 

 present was, therefore, a peculiarly appropriate tioie for both countries 

 that the comparison contemplated by Professor Struve should be instituted. — 

 The Astronomer Roval said that the standard now in progress under the 

 superintendence of the commissioner was being executed with such 

 extreme accuracy, that he felt convinced that it would not difler from what 

 it was intended to represent beyond the minute fraction of the 100,000th 

 part of an inch. He begged to ask M. Slruve whether the relation he had 

 stated between the English foot and Russian Sngcne was strictly or only 

 approximately exact ? — M. Struve replied that it was a matter determined 

 by law ; and that hence the Russian Sugenc had to be varied whenever 

 the English foot was changed. That hence the comparison had lo be made 

 with rigid accuracy when Captain Kater's determinations had been con- 

 cluded, as well as on other occasions besides the present. 



" Oil some Recent and Remarkable E.xamples of the Protection afforded btj 

 Metallic Conductors against Hcari/ Strokes of Lightning." — By Sir W. S. 

 Harris. 



The possibility of guarding buildings and other structures against the 

 destructive eflects of lightning, has been made a great question in practical 

 science — from the time of Franklin to the present day ; and it is of con- 

 siderable public importance, seeing the damage which occurs to onr 

 beautiful churches and other edifices by strokes of lightning, to bring this 

 question completely under the dominion of induction, observation, and 

 experiment. The general principles which Sir W. S. Harris sutmiitted 

 as deducible from the inquiries to which he alluded are these : — If we 

 imagine a ship or building to consist altogether of metallic substances, 

 it would certainly be secure from any damage by lightning ; and for this 

 simple reason, that what we call lightning is the result of the electrical 

 agency forcing a path through resisting matter such as tlie air, and extri- 

 cating with explosive and expansive force, both light and heat in its 

 course, AA hen, on the contrary, it falls upon comparatively non-resisting 



bodies, such as the metals, then this form of lightning vanishes, and the 

 discharge assumes, if the metallic body be suiBciently rapacious, the form 

 of a comparatively quiescent current. Our object should be, therefore, 

 in defending any building or ship from lightning, lo bring the general mass 

 so far as possible into that passive or comparatively non-resisting state it 

 would have supposing it a mass of metal. This is, in fact, the single and 

 simple condition of such an application, without any reference whatever to 

 assumed forces of allraction or peculiar specific powers manifested by 

 cerlain bodies for the matter of lightning, and which really do not eust. 

 This simple principle, by a careful mechanical arrangement, calculated to 

 render it practical and applicable to all the duties which the general 

 structure of a ship together with its masts has to perform, is now 

 universally carried out in the navy, with the most perfect success ; so that 

 damage by lightning in the vessels so fitted has, for the last fifteen years, 

 quite ceased. The masts are made completely conducting by capacious 

 plates of copper, reaching from the highest points to the keel; and are 

 tied into one general connection with all the great metallic masses 

 employed in the construction of the hull, and united by the large bolts 

 of copper passing through the keel and sides, with the copper expanded 

 over the bottom and with the sea. It is quite impossible that a discharge 

 of lightning can fall on the vessel in any place, and not be at once trans- 

 mitted safely by the conductors, not under ihe form of lightning, bnt 

 under Ihe form of a current without explosion. Sir W. Harris then 

 referred to some remarkable cases. 



" On Ancient Sea Margins." By Mr. R. Chambers. 



The existence of marine detritus containing recent shells at various heights 

 above the present sea level has long been well known. These deposits 

 are sometimes met with at an elevation of 1,2U0 or 1,300 feet — and 

 much more frequently at lower levels. They often appear in the form 

 of ancient sea-beaches or terraces, marking periods in which the relative 

 level of land and sea remained stationary. Indications of this kind abound 

 on all Ihe coasts of Great Britain, Ireland, and France, and are also seea 

 more inland. The sea has left traces of its presence sometimes by wear- 

 ing away the coast into hollows and caverns, at others by tilling up hol- 

 lows with sand and shingle, or funning rude platforms at the bases of cliffs. 

 In shores of moderate inclination these effrcts are most conspicuous; since 

 on coasts having a very small inclination the sea makes little impression, 

 whilst on a bold coast no accumulation remains. The valleys of rivers 

 also afford memorials of the former presence of the sea. Many of them 

 were once estuaries, and still exhibit terrace banks and platforms of 

 detritus brought down from distant mountains. The nature of the deposit 

 marking the margin of the ancient sea varies with situation and circum- 

 stance, being arenaceous or gravelly, clayey, or alluvial. The author has 

 examined numerous examples of these deposits on the coasts and in the 

 valleys of Scotland and England, and measured their elevation above the 

 sea. He finds them most constantly and well marked at certain particular 

 levels, which he has called, for the sake of distinction, after the places 

 where the phenomenon is most strikingly exhibited. 



The yrrsHevel at which indications of the former action of the sea are 

 found is only about 11 feet above high water. The second is from 22 to 40 

 feet above Ihe sea, and termed by the author the Chichester Beach. The 

 third terrace is G4 feet high on the seaward side, rising to SO feet inland, 

 and called the St. Andrew's Beach, being well marked near that Univer- 

 sity. The fourth, or Kingstown Beach, is from 98 to 100 feet above the 

 sea, and is seen only in a few places — as for example, near Inverness, and 

 at Kingstown, near Dublin. The fifth, or Paxlon Beach, from 114 to 128 

 feel. The sixth, or Bourland Beach, is very generally found at 16S feet 

 above the sea. The .wrcnM, or Paris Beach, from 180 to 186 feet. The 

 eighth from 275 lo 280 feet : and the ninth, or Versailles Beach 380 feet. 



Besides these, there are at some localities indications of the sea margin 

 at other heights, and marking stationary periods of briefer duration. One 

 of these, at the height of 50 feet, is visible on the shores of the Firths of 

 Tay and Forth ; others occur at elevations of 113, 130, 150 feet, and near 

 Peebles there is one at 545 or 547 feet. 



The following districts were described by the author as presenting 

 examples of a succession of sea margins a' many or all of their levels; 

 — Ihe valleys of the Ness and Spey, the Firths of Tay and Forth, 

 St. Andrew's, the Vale of Ihe Esk, Preston, Liverpool, and Birken- 

 head, at G4 to 70 feet, and again at 128 feel; Bristol, at 280 feet; 

 M'eslonsuper-Mare and Brent Knoll, at 158 feet ; Bath, at 180 feet; 

 Chichester; in the Isle of Might, Osborne House stands on the Paris 

 Beach at 181 feet; Exeter; Torbay ; London, where Mary-le-bone repre- 

 sents the St. Andrew's Beach, at 05 feet, and Deptford at 64 feet ; Paris, 

 along the line of the barriers, at 186 to 196 feet ; Rouen exhibits the St. 

 Andrew's Beach at 69 feel, and the Paxlim Beach at 120 feet, whilst the 

 table land around is 540 feel ; the Pont lie I'Aide, a broad terrace at 186 

 feet, and Dublin, a succession of sea margins at 60, 107, 139, 171, 272, and 

 280 feet. 



The author considers it probable that this uniformity in the level of Ihe 

 successive margins of the ancient sea will be found to extend also to Nor- 

 way and perhaps to North America. On the shores of the Allen Fiord 

 are a succession of terraces, considered by Bravais to form part of only a 

 single line of sea level, one extremity of which has remained station- 

 ary, whilst the other has been elevated several hundred feet. Mr. 

 Chambers, however, states that the interinediale elevations correspond 

 in level with his series of terraces, and believes they were formed 

 at the same successive periods. Along the shores of the great Ameri- 



