FARMERS' INSTITUTES. 151 



Forces Utilized by Macliinery. 



Another great consideration is this : Macliines enahle ns to perform useful 

 labor with force that would otherwise would be of little or no account. To this 

 class belong all our powerful and costly machines, including all those that move 

 by steam power, by water power, and by electricity. If no objections, we shall 

 increase this list, and include all those that are run by horse power ; for cer- 

 tainly horse power would be of no benefit without some contrivance or machinery. 

 The various animal forces, also heat, electricity, and gravity are made of prac- 

 tical utility to man only by aid of machines. Gravity gives weight to all bodies 

 on the earth, and is the force which finally brings a moving body to rest, or 

 causes a body to fall. It is gravity that causes the descending water of the 

 torrent to tremble, to shake, to foam, and to move with the velocity of the light- 

 ning over the cataract ; but it is only through machinery that this velocity and 

 this power can be utilized and made to do the former laborious work of man. 



Electricity is a force of which as yet but little is known, but by aid of 

 machinery we magnetize hundreds and even thousands of miles of soft iron wire 

 in an instant, and attract a bit of iron on the other end. We drop the key and 

 the wire is as instantly unmagnetized, and the bit of iron on the other end falls, 

 producing the familiar click of the telegraph sounder. Thus we make this 

 subtle force a medium of conversation, and force it to be our principal means of 

 raj)id communication. Besides this use for telegraphy it has been made the 

 motive power for engines. 



Heat is not usually regarded as a force, though it is a well-known fact that as 

 substances absorb heat they increase in length, or as it is usually said, "they 

 expand." The principal use of heat in connection with machinery is in con- 

 verting water into the steam ^\ liich is the apparent motive power of the steam 

 engine. 



Though steam as a motive power is being used to a certain extent to run agri- 

 cultural machines, yet, on account of the danger attending the use of fire, and 

 also on account of the high salaries of skillful engineers, it is not probable that 

 it will come into any general use for some time to come. Most of the motive 

 power needful for agricultural purposes can come only from animal forces, and 

 fortunately we have machines that may be run by appljdng these forces in a 

 variety of ways. For instance, we have the tread power, which is run by the 

 weight of the animal ; the ordinary rotary power, in which the motive force is 

 obtained by the animal pulling while walking in the circumference of a circle ; 

 and machines whose power is developed by the animal continually moving in one 

 direction. 



Action of Macliines. 



The action of a machine is to produce motion against a resistance. For 

 instance, if the machine is one for lifting solid bodies, as a crane, or fluid bodies, 

 a pump, the action is to produce upward motion of the lifted body against the 

 resistance arising from its weight. If the machine is one for propulsion, as the 

 locomotive, its action is to produce motion of a load against the resistance aris- 

 ing from friction and from gravity. If a mowing machine, the action is to 

 produce such a motion in certain parts a5 shall overcome the resistance of the 

 standing grass. 



Lost Worh — Friction. 



Should we measure the amount of force transmitted to the mowing machine 

 by the team that pulls it, we would find it considerably in excess of that needed 



