39* 



NATURE 



[August 24, 1882 



M. de Lesseps in its speedy accomplishment. Through it, 

 China, Japan, and ihe whole of the Pacific Ocean will be 

 brought to half their present distance, as measured by the length 

 of voyage, and an impulse to navigation and to progress will 

 thus be given which it will be difficult to overestimate. 



Side by side with this gigantic work, Captain Eads, the 

 successful improver of the Mississippi navigation, intends to 

 erect his ship-railway, to take the largest vessels, fully laden 

 aud equipped, from sea to sea, over a gigantic railway across 

 the Isthmus of Tehuantepec, a distance of ninety-five miles. 

 Mr. Baraaby, the chief constructor of the navy, and Mr. John 

 Fowler have expressed a favourable opinion regarding this 

 enterprise, and it is to be hoped that both the canal and the 

 ship-railway will be accomplished, as it may be safely antici- 

 pated that ihe traffic will be amply sufficient to support both 

 these undertakings. 



Whether or not M. de Lesseps will be successful also in 

 carrying into effect the third great enterprise with which his 

 nme has been prominently connected, the flooding of the Tunis- 

 Algerian Chotts, thereby re-establi hing the Lake Tritonis of 

 the ancients, with its verdure clad shores, is a question which 

 cculd only be decided upon the evidence of accurate surveys, 

 but the beneficial influence of a large sheet of water within ihe 

 African desert could hardly be matter of doubt. 



It is with a feeling not unmixed with regret that I have to 

 record the completion of a new Eddystone Lighthouse in sub- 

 stituti m for the chef-tfauvre of engineering erected by John 

 Smeaton more than 100 years ago. The condemnation of that 

 structure was no', however, the consequence of any fault of 

 construction, but was caused by inroads of the sea upon the rock 

 supporting it. The new lighthousp, designed and executed by 

 Mr., now Sir James Douglas, engineer of Trinity House, has 

 been erected in the incredibly short time of less than two years, 

 and bids fair to be worthy of its famed predecessor. Its height 

 above high water is 130 feet, as compared with 72 feet, the 

 height of Telford's s'ructure, which gives its powerful light a 

 considerably increased range. The system originally suggested 

 by Sir William Thomson some years ago, of distinguishing one 

 light from another by flashes following at varied intervals, has 

 been adopted by the Elder Brethren in this as in other recent 

 lights in the modified form introduced by Dr. John Hopkinson, 

 in wh'ch the principle is applied to revolving lights, so as to 

 obtain a greater amount of light in the flash. 



The ge -logical difficulties which for sometime threatened the 

 accomplishment of the St. Gothard Tunnel, have been happily 

 overcome, and this second and most important sub-Alpine 

 thoroughfare now connects the Italian railway system with that 

 of Switzerland and the south of Germany, whereby Genoa will 

 be constituted the shipping port for those parts. 



Whether we shall be able to connect the English with the 

 French rail *ay system by means of a tunnel below the English 

 Channel U a question that appears dependent at this moment 

 rather upon military and political than technical and financial 

 considerations. The occurrence of a stratum of impervious grey 

 chalk, at a convenient depth below the bed of the Channel, 

 minimises the engineering difficulties in the way, and must 

 influence the financial question involved. The protest lately 

 raised against its accomplishment can hardly be looked upon as 

 a public verdict, but seems to be the result of a natural desire to 

 pause pending the institution of careful inquiries. These in- 

 quiries have been made by a Royal Scientific Commission, and 

 will be referred for further consideration to a mixed Parliamen- 

 tary Committee, upon whose Report it must depend w hether the 

 natural spirit of commercial enterprise has to yield in this 

 instance to political and military considerations. Whether the 

 Channel Tunnel is constructed or not, the plan proposed some 

 years ago by Mr. John Fowler of connecting England and 

 France by means of a ferry boat capable of taking railway trains 

 would be a desideratum just. tied by the ever-increasing inter- 

 communication between this and Continental countries. 



The public inconvenience arising through the obstruction to 

 traffic by a sheet of water is well illustrated by the circumstance 

 that both the estuaries of the Severn and of the Mersey are being 

 undermined in order to connect the railway systems on the two 

 sides, and that the Frith of Forth is about to be spanned by a 

 bridge exceeding in grandeur anything as yet attempted by the 

 engineer. The roadway of this bridge will stand 150 feet above 

 high-water mark, and its two principal spans will measure a 

 third of a statute mile each. Messrs. Fowler and Baker, the 

 engineers to whom this great work has been entrusted, could 



hardly have accomplished their task without having recourse to 

 steel for their material of construction, nor need the steel used 

 be of the extra mild quality particularly applicable for naval 

 structures to withstand collision, for, when such extreme tough- 

 ness is not required, steel of very homogeneous quality can be 

 produced, bearing a tensile strain double that of iron. 



The tensile strength of steel, as is well known, is the result of 

 an admixture of carbon with the iron, varying between ftyh 

 and 2 per cent., and the nature of this combination of carbon 

 with iron is a matter of great interest both from a theoretical and 

 practical point of view. It could not be a chemical compound 

 which would neces State a definite proportion, nor could a mere 

 dissolution of the one in the other exercise such remarkable 

 influence upon the strength and hardness of the resulting metal. 

 A recent investigation by Mr. Abel has thrown considerable 

 light upon this question. A definite carbide of iron is formed, 

 it appears, soluble at high temperatures in iron, but separating 

 upon cooling the steel gradually, and influencing only to a mode- 

 rate degree the physical properties of the metal as a whole. In 

 cooling rapidly there is no time for the caibide to separate from 

 the iron, and the metal is thus rendered both hard and brittle. 

 Cooling the metal gradually under the influence of great com- 

 pressive force, appears to have a similar effect to rapid cooling 

 in preventing the separation of the carbide from the metal, with 

 this difference, that the effect is more equal throughout the mass, 

 and that more uniform temper is likely to result. 



When the British Association met at Southampton on a 

 former occasion, Schonbein announced to the world his dis- 

 covery of gun-cotton. This discovery has led the way to many 

 valuable researches on explosives generally, in which Mr. Abel 

 has taken a leading part. Recent investigations by him, in con- 

 nection with Captain Noble, upon the explosive action of gun- 

 cotton and gunpowder confined in a strong chamber, which have 

 not yet been published, deserve particular attention. They 

 show that while by ihe method of investigation pursued about 

 twenty years ago by Karolye (of exploding gunpowder in very 

 small charges in shells confined within a large shell partially 

 exhausted of air), the composition of the gaseous products was 

 found to be complicated and liable to variation, the chemical meta- 

 morphosis which gun-cotton sustains, when exploded under condi- 

 tio 11s such as obtain in its practical application, is simple and very 

 uniform. Among other interesting pints noticed in this direction 

 wa the fact that, as in the case of gunpowder, the proportion of car- 

 bonic acid increases, while that of carbonic oxide diminishes with 

 the density of the charge. The explosion of gun-cotton, whether 

 in the form of wool or loosely spun thread, or in the packed 

 compressed form devised by Abel, furnished practically the same 

 results if fired under pressure, that is, under strong confinement 

 — the conditions being favourable to the full development of its 

 explosive force ; but some marked differences in the composition 

 of the products of metamorphosis were observed when gun- 

 cotton was fired by detonation. With regard to the tension 

 exerted by the products of explosion, some interesting points 

 were observed, which introduce very considerable difficulties 

 into the investigation of the action of fired gun-c>tton. Thus 

 whereas no marked differences are observed in the tension 

 developed by small charges and by very much larger charges of 

 gunpowder having the same density (i.e., occupying the same 

 volume relatively to the entire space in which they are exploded) 

 the reverse is the case with respect to gun-cotton. Under 

 similar conditions in regard to density of charge, 100 grammes 

 of gun-cotton gave a measured tension of about 20 tons on the 

 square inch, 1,500 grammes gave a tension ot about 29 tons (in 

 several very concordant observations), while a charge of 2 '5 kilos 

 gave a pressure of about 45 tons, this being the maximum mea- 

 sured tension obtained with a charge of gunpowder of five times 

 the density of the above. 



The extreme violence of the explosion of gun cotton as com- 

 pared with gunpowder when fired in a closed space was a 

 feature attended with formidable difficulties. In whatever 

 way the charge was arranged in the firing cylinder, if it had 

 free access to the enclosed crasher gauge, the pressures re- 

 corded by the latter were always much greater than when 

 means were taken to prevent the wave of matter suddenly set 

 in 1111 -lion from acting directly upon the gauge. The abnormal 

 or wave-pressures recorded at the same time that the general 

 tension in the cylinder was measured amounted in the experi- 

 ment to 42*3 tons, w hen the general tension was recorded at 

 20 tins ; and in another when the pressure was measured at 29 

 ton , the wave-pressure recorded was 44 tons. Measurements 



