d 2 I
fP = 0.65 p  ------- - R
D

renders it impossible to pronounce upon it before the trials earnestly and justly demanded by the author of this new system.  In present practice f = 1/7 is admitted.  M. Nansouty gives in a table a resume of the experience on this subject, and goes on: 

“The English engineers, as will be seen, make a single axle support more than 17 tons.  In France the maximum weight admitted is 14 tons, and the constructor of the Estrade locomotive has kept a little below this figure.  The question of total weight appears to be secondary in a great measure, for, taking the models with uncoupled wheels, the English engines for great speed have on an average, for a smaller total weight, an adhesion equal to that of the French locomotives.  The P.L.M. type of engine, which has eight wheels, four of which are coupled, throws only 28.6 tons upon the latter, being 58 per cent. of the total weight.  On the other hand, that of the English Great Eastern throws 68 per cent. of the total weight on the driving wheels.  Numerous other examples could be cited.  We cannot, we repeat, give an opinion rashly as to the calculation of adhesion for the high speed Estrade locomotive before complete trials have taken place which will enable us to judge of the particular coefficients for this entirely new case.”

M. Nansouty then goes on to consider the question of curves, and says: 

“It has been asked, not without reason, notably by the Institution of Civil Engineers of Paris, whether peculiar difficulties will not be met with by M. Estrade’s locomotive—­with its three axles and large coupled wheels—­in getting round curves.  We have seen in the preceding tables that the driving wheels of the English locomotives with independent wheels are as much as 8 ft. in diameter.  The driving wheels of the English locomotives with four coupled wheels are 7 ft. in diameter.  M. Estrade’s locomotive has certainly six coupled wheels with diameters never before tried, but these six coupled wheels constitute the whole rolling length, while in the above engines a leading axle or a bogie must be taken into account, independent, it is true, but which must not be lost sight of, and which will in a great measure equalize the difficulties of passing over the curves.

“Is it opposed to absolute security to attack the line with driving wheels?  This generally admitted principle appears to rest rather on theoretic considerations than on the results of actual experience.  M. Estrade, besides, sets in opposition to the disadvantages of attacking the rails with driving wheels those which ensue from the use of wheels of small diameter as liable to more wear and tear.  We should further note with particular care that the leading axle of this locomotive has a certain transverse play, also that it is a driving axle.  This disposition is judicious and in accordance with the best known principles.”