THE FARMER AT HOME. 175 



imount of crops, and the profits of the farmer, it deserves serious con- 

 sideration . 



FRICTION. Denotes the resistance a moving body meets with 

 from the surface, on which it moves. Friction arises from the rough- 

 ness or asperity of the surface of the body moved on, and that of the 

 body moving ; for such surfaces consisting alternately of eminences 

 and cavities, either the eminences of the one must be raised over those 

 of the other, or they must be both broke and worn off; but neither 

 can happen without motion, nor can motion be produced without a 

 force impressed. Hence, the force applied to move the body is either 

 wholly or partly spent, on this effect ; and consequently there arises 

 a resistance, or friction, which will be greater, other things being 

 equal, as the eminences are the greater, and the substance the hard- 

 er ; and as the body, by continual friction, becomes more and more 

 polished, the friction diminishes. 



A very large part of the power requisite to move a threshing ma- 

 chine, a wagon, or a plough, is expended in overcoming the passive 

 resistance of simple friction ; and the greater in any case the space 

 on which this acts, the greater will be the force required to overcome 

 it. A wagon, the axles of which run on rollers, where the friction 

 is reduced to its minimum, will move over a surface with much less 

 force applied, than one where the whole surface of the axle comes in 

 contact with the inner part of the hub, and the friction of course is 

 at its maximum. The experiments of Mr. Pusey of the English 

 Royal Agricultural Society, proved that in all soils the celebrated 

 Scotch plough, and consequently all ploughs similarly constructed, 

 which, from its structure of share and mould-board, exposes a great 

 extent of surface to friction, was so much impeded from that cause, 

 that a large part of the power of the team was expended in overcom- 

 ing it ; and that in tenacious soils at least one-half of the force ex- 

 erted was required to overcome the effect of this cause. It is clear, 

 then, that a light plough, with a part of the weight supported on a 

 wheel or wheels, and with the least possible surface exposed to fric- 

 tion, will move the easiest for the team ; and in all implements and 

 machinery, the lessening of the friction is one of the most important 

 things to be aimed at in their construction. 



FROG-. The external figure of the frog is too well known to 

 require being particularly described ; its active powers are astonish- 

 ingly great, when compared with its unwieldy shape ; it is the best 

 swimmer of all four-footed animals ; and Nature has finely adapted 

 it for those ends ; the arms being light and pliant, the legs long, and 

 endowed with great muscular strength. A single female produces 

 from six to eleven hundred eggs at a time ; but this only happens 

 once a year. The male is of a greyish brown color ; but the skin oi 

 the female is of a yellow hue ; these colors grow deeper every time 

 they change them, which frequently happens every eighth day. The 



