April 22, 1886] 



NA JURE 



579 



the same time it is'not improbable that'the first outbursts 

 may be dated back to the later Eocene, and the last to 

 the period when the waters of the great Jordan-Valley 

 Lake had receded from their original limits to those 

 within which they are now restricted. 



The physical details form but a small part of the 

 volume, which contains a large number of carefully drawn 

 figures of works of art and architecture, accompanied by 

 descriptive text, showing that the region, now the abode 

 of Fellahin — or of migratory. Arabs — was one of import- 

 ance during long centuries of successive dynasties and 

 races. The book cannot fail to be of value to students of 

 Biblical and ancient history, and we are promised by 

 Herr Schumacher descriptive drawings and maps of 

 another section of the Hauran country. 



HARBOURS 

 The Design and Construction of Harbours. A Treatise 

 on Maritime Engineering. By Thomas Stevenson, 

 P.R.S.E., &c. Third Edition. Pp. xiv. + 355. 

 Twenty-four Plates. (Edinburgh : A. and C. Black, 

 18S6,) 



THIS work is a reprint, with large and valuable addi- 

 tions, of the article " Harbours " in the Encyclo- 

 pffidia Britannica." Its importance may be gauged from 

 its acceptance in successive editions of that " Encyclo- 

 pjedia, and from its having passed into three editions in 

 the separate and enlarged form. 



An important feature is the attempt to lay down gene- 

 ral principles, and to discuss and reduce as far as possible 

 to calculation the effect of the great forces of wind and 

 water, and to regulate both the general design and the 

 details of constructions thereon. To the earlier engineers 

 this was mere guesswork, e.g. Smeaton is said (p. 41) to 

 have described these forces as " subject to no calculation." 

 Many striking instances of the maximum effect of wind 

 and waves are given, e.g. at the top of Whalsey Skerries 

 (Zetland), at a height of 74 feet above high water, large 

 blocks up to 132 tons were found to have been lifted and 

 transported by the waves (p. 45). Again, two blocks of 

 1350 tons and 2600 tons were shifted bodily at the Wick 

 breakwater in two storms in 1872 and 1877. At Dunbar, 

 pressures of 3i tons per square foot for the direct wave- 

 action (p. 56), and of I ton per square foot for the back- 

 wash (p. 131), were recorded upon a dynamometer of the 

 author's invention ; and, by use of two instruments at 

 different levels, it was found that the pressure at the 

 upper level may (exceptionally ?) be twice that at the 

 lower level (p. 56). It is much to be wished that ex- 

 tensive and systematic observations of this kind were 

 made, as instances are quoted wherein only 80, 144, and 

 70 lbs. per square foot had been assumed in the design 

 of lighthouses and harbours (p. 58). Scott Russell's 

 opinion is quoted (p. 106), and accepted, that the most 

 violent action on sea-works is from those waves^which 

 form ground-swell or rollers, and are " waves of transla- 

 tion," i.e. vast masses of solid water moving horizontally 

 with great velocity ; and that the only way of opposing 

 them is by masses too heavy for them to move. 



A useful feature of the work is the presentation of 

 28 cross-sections of quay-, dock-, and harbour-walls, and 

 breakwaters, beginning with the jetty of old] Dunkirk 



(1699) ; also of 10 cross-sections of lighthouses, beginning 

 with Winstanley's Eddystone (1699). 



A chapter (47 pp.) is devoted to materials. A good 

 deal is said about their decay under water. No ordinary 

 material seems free from this. All timber is eventually 

 destroyed by borers (oddly termed insects in this work !) 

 of diflerent sorts ; even greenheart and creosoted timber, 

 till recently thought borer-proof, have now given way to 

 their special borers. Most stone, and even rock in situ, 

 has its own special borer. Iron gives way by rusting, 

 perhaps at a rate of three-quarters of an inch in a 

 century. Bronze alone seems to stand sea-water, but is 

 too expensive to be extensively used. 



Ten pages are given to the use of Portland cement 

 concrete, and some remarkable instances of its use are 

 detailed, e.g. the concrete cylinder foundations (12 feet 

 diameter, 30 feet length) of the Plantation Quay at Glas- 

 gow, and the use of 350-ton blocks (say 5000 cubic feet) 

 laid in 24 feet of water at Dublin (1885). 



Attention is drawn to a new and seemingly very pro- 

 mising .-\merican cement styled " carbonite," which is 

 said to stand an ultimite pressure of Sooolbs. per square 

 inch, or eight times as much as Portland cement. Trial 

 of this cement in England is much to be wished. Its 

 preparation is apparently a secret, as though four pages 

 are devoted to its use and properties, its main ingredients 

 are only hinted at as being various hydrocarbons. 



Two chapters (39 pp.) are given to the difficult subjects 

 of training works for preserving the outfall of harbours 

 and rivers, and preventing silting in estuaries. An inter- 

 esting instance of the great commercial advantage of 

 even a small increase of depth in a harbour is that of 

 Leith, where an addition of only 2 feet of depth at the 

 Albert Dock gave 296 tides yearly of 23 feet depth 

 against 102 tides of that depth at the Victoria Basin. 



Attention is drawn to the disadvantage of harbours 

 being constructed as local instead of as national works. . 

 Want of funds has thus repeatedly led to harbours being 

 designed too small for future wants, and being afterwards 

 enlarged at greatly increased cost, the whole works 

 having to be destroyed to make way for the new. 



One of the least satisfactory parts of this work is the 

 formulae, the range of applicability of several of the em- 

 pirical ones being very doubtful. One (which should have 

 been definite) on strength of lock-gates (p. 191) is mis- 

 printed 



5 = 1 IVstc (f> + Jj cosin (f>. 



By reference to the original (Trans. Inst.C.E., vol. i. p. 67) 

 it is seen to be 



S = ^ r-Fsec </> + .J a JKcosec 4'- 

 Moreover, the meaning of IV is misquoted as "pressure 

 on the length of the gate, &c.," instead of " pressure on 

 the length /, &c." (/ being only the half-breadth of lock), 

 and the meaning of the result .S" is given, in words which 

 are barely intelligible, as " whole transverse strain at 

 angle <f>": the context of the original shows that this 

 should be " whole transverse strain applied at middle of 

 gate " (strain being understood to mean pressure). These 

 defects occur in the "Encyclopaedia Britannica" (9th ed.) 

 as well as in the separate work (3rd ed.). 



(jn p. 243 a table of values of a "constant" of strength 

 of various timbers is given without explanation of the 

 meaning of the " constant." 



