The mileage changed of the L&N. and E.T., V.& G. systems combined aggregates 3,622 miles. The total cost of these two roads. $331,492.59 Or an average per mile of 91.52 Total miles changed was about 14,500 miles. Which would give total cost, at same rate. $1,327,040 We should really add to this a large sum for the great number of new locomotives which were purchased to replace old ones, that could not be changed, except at large cost, and which, when done, would have been light and undesirable. Upon the basis of the work done upon the L. & N. and E.T., V. & G. systems, which, combined, cover about one-fourth the mileage changed, we have made the following estimates, which will, perhaps, convey a better idea of the extent of the work than can be obtained in any other way: Miles of track changed, about 14,500 Locomotives changed, about 1,800 Cars (pass, and freight) changed, about 45,000 New axles used, about 9,000 New wheels used, about 20,000 Axles turned back, about 75,000 Wheels pressed on without turning axles, about 220,000 New brasses used, about 90,000 Kegs of spikes used, about 50,000 Cost of material used, about $600,000 Cost of labor, about 730,000 Total cost of work, about 1,330,000 Amount expended on equipment, about 650,000 Amount expended on track, about 680,000 Amount expended on track on day of change in labor, about 140,000 The work was done economically, and so quietly that the public hardly realized it was in progress. To the casual observer it was an every day transaction. It was, however, a work of great magnitude, requiring much thought and mechanical ability. That it was ably handled is evidenced by the uniform success attained, the prompt changing at the agreed time, and the trifling inconvenience to the public.--_Jour. Assn. Engineering Societies._ * * * * * TORPEDO BOATS FOR SPAIN. In our present issue, on page 9948, we give illustrations of two torpedo boats, the Azor and Halcon, which have lately been constructed by Messrs Yarrow & Co., of Poplar, for the Spanish government. They are 135 ft. in length by 14 ft. beam, being of the same dimensions as No. 80 torpedo boat, lately completed by the above firm for the Admiralty, which is the largest and fastest torpedo-boat in the British navy. [Illustration: TORPEDO BOATS FOR THE SPANISH GOVERNMENT.]