The great number of types of locomotives and carriages now met with in France, England, and the United States renders it difficult to combine their advantages, as M. Estrade proposed to do, in a system responding to the requirements of the constructor.  His principal object, however, has been to construct, under specially favorable conditions, a locomotive, tender, and rolling stock adapted to each other, so as to establish a perfect accord between these organs when in motion.  It is, in fact, a complete train, and not, as sometimes supposed, a locomotive only, of an especial type, which has been the object he set before him.  Before entering into other considerations, we shall first give a description of the stock proposed by M. Estrade.  The idea of the invention consists in the use of coupled wheels of large diameter and in the adoption of a new system of double suspension.

The locomotive and tender we illustrate were constructed by MM.  Boulet & Co.  The locomotive is carried on six driving wheels, 8 feet 3 inches in diameter.  The total weight of the engine is thus utilized for adhesion.  The accompanying table gives the principal dimensions: 

TABLE I.

+---------------------------------------+
|                       | ft. in.       |
+-----------------------+---------------+
|Total length of engine.| 32  8         |
+-----------------------+---------------+
|Width between frames.  |  4  1         |
+-----------------------+---------------+
|Wheel base, total.     | 16  9         |
+-----------------------+---------------+
|Diameter of cylinder.  |  1  61/2        |
+-----------------------+---------------+
|Length of stroke.      |  2  31/2        |
+-----------------------+---------------+
|Grate surface.         | 25 sq. feet.  |
+-----------------------+---------------+
|Total heating surface. | 1,400 sq. ft. |
+-----------------------+---------------+
|Weight empty.          | 38 tons.      |
+-----------------------+---------------+
|Weight full.           | 42 tons.      |
+---------------------------------------+

The high speeds—­77 to 80 miles an hour—­in view of which this stock has been constructed have, it will be seen, caused the elements relative to the capacity of the boiler and the heating surfaces to be developed as much as possible.  It is in this, in fact, that one of the great difficulties of the problem lies, the practical limit of stability being fixed by the diameter of the driving wheels.  Speed can only be obtained by an expenditure of steam which soon becomes such as rapidly to exhaust the engine unless the heating surface is very large.

The tender, also fitted with wheels of 8 ft. 3 in. in diameter, offers no particular feature; it is simply arranged so as to carry the greatest quantity of coal and water.