150 STATE BOAED OF AGKICULTUKE. 



You Avell know liow you can make one pound balance two pounds, — or in 

 otlier words, how a man weighing 150 j)ound3 can raise any thing less than 300 

 jiounds ; but you notice that the lever arm on which he works is twice the length 

 of that of the weight, and that he moves twice as fast, or passes through any 

 given space in half the time that the weight occupies in going through. So it 

 is with all machinery, from the simple grindstone to the complicated time-piece ; 

 from the horse pitch-fork to the steam locomotive. All recognize the great law 

 that any increase of power is always accompanied by a corresponding loss, 

 either of velocity or of time ; and vice versa, any increase of velocity, and con- 

 sequent saving of time, can only be done at the expense of power. An example 

 of this last is seen in the steam locomotive. When the driver Avishes to go faster 

 he cither reduces his load or increases his head of steam, which constitutes the 

 driving power ; but in no case can he increase his velocity without first increas- 

 ing his power, or, what has the same effect, reducing his load. 



The second law is that of moinentum, whose poAverful effects deserve a few 

 remarks. Its great force is shown by such simple operations as driving nails 

 with a hammer, or wedges with a beetle. The weight of the hammer with the 

 strength of the arm added would not drive the nail, but the momentum, — that 

 is, the combination of velocity and weight, — does the work in an instant. 

 Inventors of machinery are sometimes much puzzled because of the failure of 

 full-sized machines, where models have worked perfectly. They did not take 

 into account the enormous increase of momentum caused by increasing the 

 parts. For instance, if a model six inches long be made into a machine five feet 

 long, the momentum of the moving parts will be 10,000 times increased. This 

 fact should lead us to be cautious in tlie purchase of implements or machinery 

 of any kind from seeing the work of a model. N"o neAV implement should be 

 purchased Avithout an exhaustive and satisfactory trial of a working machine. 



WorJc of a JlacJiine. 



The sole work of a machine, Avliatever be its kind, consists in transmitting 

 and modifying force or motion. There is no machine, nor can there be any, 

 that will give any increase of both poAver and velocity. There are an endless 

 variety of machines that Avill giA'e a marked increase of one of these, but investi- 

 gation Avill invariably shoAV that this increase is accompanied by a corresponding 

 decrease of the other. 



In the yards of the copper-smelting works at Detroit there is a large crane, 

 by means of Avhich eighteen tons can easily be lifted by six men. Now the men 

 do not exert over 80 pounds of force apiece, consequently Ave have 480 poiTnds of 

 force lifting 3C,000 pounds, or one pound of force lifting 75 pounds. But we 

 notice another thing, Adz., that it takes 75 revolutions of the driving-Avheel to 

 produce one revolution of the drum or Avheel that does the lifting. Consequently, 

 although the men lift 75 times as much as they could Avithout the aid of the 

 crane, they nevertheless are required to move 75 times as far. 



The great advantage of machines is found principally in this one thing : they 

 giA'e us poAver when Ave Avant it, or they give us velocity Avhen Ave Avant it. Of 

 Avhat use would velocity be in the crane? None at all; and it might even be, 

 damaging, as a body as heavy as 18 tons, moving Avitli much speed, Avould be 

 not only uuAvieldy, but positively dangerous. Again, in the case of the buzz-saw 

 Ave need a great deal of velocity, and A^ery little or no lifting poAver ; but in order 

 to get that velocity Ave require the united strength of ten horses. 



