ai8 THE POPULAR SCIENCE MONTHLY. 



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 which the principle is applied to revolving lights, so as to obtain a 

 greater amount of light in the flash. 



The geological difficulties which for some time threatened the ac- 

 complishment of the St. Gothard Tunnel have been happily overcome, 

 and this second and most important sub- Alpine thoroughfare now con- 

 nects 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 

 railway system by means of a tunnel below the English Channel is a 

 question that appears dependent at this moment rather upon military 

 and political than technical and financial considerations. The occur- 

 rence of a stratum of impervious gray chalk, at a convenient depth 

 below the bed of the Channel, minimizes 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 inquiries 

 have been made by a Royal Scientific Commission, and will be referred 

 for further consideration to a mixed Parliamentary Committee, upon 

 whose report it must depend whether the natural spirit of commercial 

 enterprise has to yield in this instance to political and military consid- 

 erations. 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 justified by the ever-increasing intercommu- 

 nication 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 grand- 

 eur anything as yet attempted, by the engineer. The roadway of 

 this bridge will stand one hundred and fifty 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 intrusted, 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 

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

 produced, bearing a tensile strain double that of iron. 



