3 2o THE POPULAR SCIENCE MONTHLY. 



effects. The employment of suspending springs has rendered the 

 double service of suppressing injurious vibrations and of collecting 

 into a useful form all the work which they represent. 



Is this all ? Do there not remain, even with the best carriages, 

 other vibrations and other shocks which must be pursued and de- 

 stroyed in order to render more perfect the conditions of traction ? 

 You have all experienced, at the moment of the sudden start of a car- 

 riage, and even at each stroke of the whip on a living horse, horizontal 

 shocks which sometimes throw you to the bottom of the carriage. In 

 a less degree, shocks of the same kind are produced at each instant of 

 traction, for the speed of the horse is far from being uniform, and the 

 traces are subjected to alternate tension and slackness. Here are veri- 

 table shocks which use up part of the work of the horse in giving only 

 hurtful effects which bruise and contuse the breast of the animal, injur- 

 ing his muscles, and, in spite of the padding of the collar, sometimes 

 wounding him. To prove the disadvantages of this kind of shocks, 

 some experiments are necessary. I have borrowed one from Poncelet ; 

 it is easily made, and any one may repeat it. I attach a weight of 

 five kilos to the extremity of a small string ; taking hold of the free 

 extremity of this, if I gently raise the weight, you see that the cord 

 resists the weight of five kilos and holds it suspended. But if I at- 

 tempt to raise the same weight more rapidly, I bruise my fingers, the 

 cord breaks, and the weight has not budged. The effort which I have 

 made has been greater than the preceding, since it has exceeded the re- 

 sistance of the cord ; but the duration of this effort has been too short, 

 and, the inertia of the weight not being overcome, all my exertion 

 has been expended in injurious work. If, instead of an inextensible 

 cord, I had attached to the weight a cord a little extensible, the sud- 

 den effort of elevation which I made would have been transformed 

 into an action more prolonged, and the weight would have been raised 

 without breaking the cord and bruising my fingers. To render the 

 phenomenon more easy of comprehension, I shall make a new experi- 

 ment under conditions a little different. 



You see on a vertical support (Fig. 1) a sort of balance-beam, 

 which bears on one of its arms a weight of one hundred grammes, on 

 the other a weight of ten grammes suspended at the end of a cord one 

 metre long. Between these two unequal weights the beam is main- 

 tained by a spring-catch, which prevents it from falling to the side of 

 the heavier weight, but which, on the other hand, permits the beam to 

 incline in the opposite direction, if we bring to bear on the end of the 

 cord an effort greater than the weight of one hundred grammes. But, 

 by letting the smaller weight fall from a sufficient height, at the 

 moment when this reaches the end of its course, it will stretch the 

 cord which holds it, and will develop what is called a vis viva, capa- 

 ble of raising the weight of one hundred grammes to a certain height ; 

 but this elevation will only take plnce on condition that the applica- 



