He goes on to consider, in the first place: Especial types of uncoupled wheels, the diameters of which form useful samples for our present case. The engines of the Bristol and Exeter line are express tender engines, adopted on the English lines in 1853, some specimens of which are still in use.[1] These engines have ten wheels, the single drivers in the center, 9 ft. in diameter, and a four-wheeled bogie at each end. The driving wheels have no flanges. The bogie wheels are 4 ft. in diameter. The cylinders have a diameter of 161/2 in. and a piston stroke of 24 in. The boiler contains 180 tubes, and the total weight of the engine is 42 tons. These locomotives, constructed for 7 ft. gauge, have attained a speed of seventy-seven miles per hour. [Footnote 1: M. Nansouty is mistaken. None of the Bristol and Exeter tank engines with. 9 ft. wheels are in use, so far as we know. ED. E.] The single driver locomotives of the Great Northern are powerful engines in current use in England. The driving wheels carry 17 tons, the heating surface is 1,160 square feet, the diameters of the cylinders 18 in., and that of the driving wheels 8 ft. 1 in. We have here, then, a diameter very near to that adopted by M. Estrade, and which, together with the previous example, forms a precedent of great interest. The locomotive of the Great Northern has a leading four-wheeled bogie, which considerably increases the steadiness of the engine, and counterbalances the disturbing effect of outside cylinders. Acting on the same principles which have animated M. Estrade, that is to say, with the aim of reducing the retarding effects of rolling friction, the constructor of the locomotive of the Great Northern has considerably increased the diameter of the wheels of the bogie. In this engine all the bearing are inside, while the cylinders are outside and horizontal. The tender has six wheels, also of large dimensions. It is capable of containing three tons and a half of coal and about 3,000 gallons of water. This type of engine is now in current and daily use in England. M. Nansouty next considers the broad gauge Great Western engines with 8 ft. driving wheels. The diameters of their wheels approach those of M. Estrade, and exceed considerably in size any lately proposed. M. Nansouty dwells especially upon the boiler power of the Great Western railway, because one of the objections made to M. Estrade's locomotive by the learned societies has been the difficulty of supplying boiler power enough for high speeds contemplated; and he deals at considerable length with a large number of English engines of maximum power, the dimensions and performance of which are too well known to our readers to need reproduction here.