270 THE FARMER AT HOME. 



instruments or machines in the hands of man. by which he is enabled 

 to raise great weights, and overcome such resistances as his natural 

 strength could never effect without them. They are six in number, 

 the lever, the pulley, the wheel and axle, the inclined plane, the 

 wedge, arid the screw, one or more of which enters into the composi- 

 tion of every machine. In order to understand the power of a 

 machine, four things are to be considered ; the power that acts, which 

 consists in the effort of men and horses, of weights, springs, running 

 waters, wind, and steam ; the resistance which is to be overcome by 

 the power, which is generally a weight to be moved ; the centre of 

 motion, or, as it is termed in mechanics, the fulcrum, which is the 

 point about which all the parts of a body move ; and lastly, the 

 respective velocities of the power, and of the resistance, which must 

 depend upon their respective distances from the axis of motion. The 

 power and weight are said to balance each other, or to be in equili- 

 brium, when the effort of the one to produce motion in one direction, is 

 equal to the effort of the other to produce it in the opposite direction. 

 The power of a machine is calculated, when it is in a state of equi- 

 librium, that is, when the power just balances the resistance opposed, 

 and the momentum of each is equal. 



MELON. A species of cucumber, indigenous in warm climates, 

 where its juicy fruit is highly acceptable. In cold ones, its coolness 

 is somewhat dangerous. The cantalupe melon is in principal estima- 

 tion. To raise melons with a proper regard to wholesomeness and 

 flavor, that water which is usually given, in order to increase their 

 size, should be kept away. 



MERCURY. This a mineral or metallic fluid, vulgarly called 

 quicksilver, and distinguished from all other metals by its extreme 

 fusibility, which is such, that it does not assume the solid state, until 

 cooled to the 39th degree below on Fahrenheit's thermometer, and 

 of course is always fluid in temperate climates. It is volatile, and 

 rises in ' small portions at the common temperature of the air ; it 

 readily combines with gold, silver, lead, tin, bismuth, and zinc, and 

 on that account is usefully employed in the silvering of looking-glasses, 

 making barometers and thermometers, and for various other purposes. 



MERIDIAN. Meridian is a great circle passing through the 

 poles of the earth, and some given place on its surface. It therefore 

 divides this surface into two hemispheres, the eastern and the western. 

 As the terrestrial meridian is the circle over which the sun is at noon, 

 it is consequently in the plane of the celestial meridian with which 

 the centre of the sun coincides at that time. Now as, by the earth's 

 revolution about its axis from west to east once in twenty-four hours, 

 every part of the equator is successively presented to the sun, all 

 places that are situated eastward or westward of each other have 

 their respective meridians. It is, therefore, always the same hour of 

 the day at all places situated on the same meridian. The first meri 



