440 



NATURE 



[March 13, 1879 



v 



the whole apparatus, but the weight of 100 grammes is 

 not raised. 



Now suspend this weight of loo grammes to an india- 

 rubber cord or an elastic spring, and repeat the experi- 

 ment. You see each time that the weight falls that the 

 loo-gramme weight is raised to a certain extent. But 

 this elevation is effected under peculiar conditions. At 

 the moment when the weight falls and the cord is 

 stretched, the balance inclines, stretching the elastic 

 spring, but the mass of loo grammes does not yet move ; it 

 is only when this spring is stretched that the mass, 

 obedient to the prolonged action of this elastic spring, 



Fig. I. — Apparatus to show that a vis viva directly applied to the displace- 

 ment of a mass is lost in a shock, while the same force transmitted by an 

 elastic medium may perform work. 



begins to move and rises, representing a certain amount 

 of work accomplished. 



Thus, the suppression of shock in traction, economises a 

 certain part of the moving labour ; it is then advantageous 

 to give to the traces of a carriage a certain elasticity. 

 One of the most simple methods consists in interposing 

 between the trace and the carriage an elastic medium. 

 Here are some of these elastic pieces, which I call tractors. 

 One of the patterns has been made by M. Tatin ; it is 

 composed of a spring which is compressed by traction 

 and deadens the shock. The other is formed of a similar 

 spring placed in the very inside of the carriage-trace. 



If you wish to be convinced of the advantage of this 

 mode of traction, voke yourself to a hand-barro-v by 



Fig. 2. — Iracing ot the dynamog aph for a vehicle drawn by a horse. 



means of a rigid leather strap, such as you see used in 

 the streets of Paris or London, where too often man is 

 employed to drag burdens, "When you have well noted 

 the painful shocks which this mode of traction transmits 

 to the shoulders, place between the strap and the barrow 

 the elastic tractor and repeat the experiment. After that 

 no doubt is possible ; the shoulders are no longer bruised 

 by the shaking of the pavement, and a comfort is expe- 

 rienced which will evidently be experienced in the same 

 degree by a horse placed in conditions of elastic traction. 

 To obviate suffering to men and animals is unfortu- 

 nately not a motive sufficient to induce everybody to 



modify the old system of harnessing. To certain minds 

 known a.s positive, it is necessary to prove that elastic 

 traction has economical advantages, and that a horse 

 thus harnessed is able to draw heavier loads. This fact, 

 which results from the experiments which you have seen, 

 requires, to be rigorously proved, the aid of the graphic 

 method. It is to the genius of Poncelet that we owe the 

 record of work expended by different motors. 



Everybody knows what a dynamometer is, viz., a spring 

 which, yielding to tractions exerted upon it, is deformed 

 in proportion to the efforts developed. Let us adapt to a 

 spring of this kind a pencil which touches a strip of 

 paper, and let us so arrange things that the movements 

 of the wheel of a carriage shall impress upon the paper 

 a motion of translation. While the effort of traction of 

 the horse will communicate to the spring movements 

 more or less extended, the progress of the carriage will 



-Tracing of the dynamograph for a vehicle drawn with an elastic" 

 intermediary. 



Fig. 



draw out the paper, and from these combined movements 

 will result a curve (Fig. 2), which can be resolved into a 

 series of ordinates or vertical lines in juxtaposition, ex- 

 pressing by their unequal heights the series of efforts 

 resulting from each element of the road traversed. The 

 sum of these elementary efforts, otherwise the surface of 

 paper limited in height by the flexures of the curve, will 

 be the measure of the work expended. If we record in 

 a comparative manner the work done by the same vehicle 

 harnessed with rigid traces or supplied with elastic trac- 

 tors, we see (Figs. 3 and 4) that the area of the curve is 

 greater, that is, that there has been more work expended, 

 while rigid traces have been used. In the most favour- 

 able cases that I have met with, the economy of work by 

 elastic traction has been 26 per cent. 



But, it may be objected, the recording dynamometer 

 itself constitutes an elastic intermediary which suppresses 



Fig. 4. — Tracing of the dynamograph for a hand-barrow drawn by a rigid 

 trace. 



the shocks. But it is not the ordinary dynamometer 

 which I have used in my experiments, but a special 

 dynamometer which undergoes under the strongest trac- 

 tions only an almost insignificant elongation. This 

 elongation, amplified by certain organs and transmitted 

 to a distance by a lever fitted with a pen, is recorded in 

 the form of a wavy curve in conditions referred to above. 

 To sum up, in the employment of animated motors for 

 the drawing of burdens, to find out wherever they produce 

 shocks and vibrations, and to absorb them in elastic 

 springs which restores to useful work a force that seemed 

 only to destroy vehicles, tear up the roads, cause the 

 animals to suffei' — such is the direction in which much 

 progress has been realised, and much more may still be 

 realised. 



2. Of the Speed, of Animated Motors. — I shall per- 



