292 APPENDIX. 



4 A C, then W will be supported by a power = } of its 

 weight. Example. If a wagon with its load weigh 40 cwt. 

 and may be drawn on level ground by a force equal to 8 

 cwt, in drawing it to the top of a hill which rises 20 yds. 

 in a XOO, the horses will have to pull with an additional 

 force =3 i of 40 cwt., that is, 8 cwt. more than on level 

 ground, or with double their former force. 



LESSON 22. 



T/ie Wedge, Jig. 6. — A BCD may be divided into two 

 inclined planes, ADC and B D C, which may be used se- 

 parately, and will gain advantage as such ; therefore, when 

 united at D C, the advantage gained will be in the same pro- 

 portion as when they were used in different parts. The 

 Screw, jig. 3. A must turn once round before the resistance 

 can be moved from one spiral winding to another, as from x 

 to z = ^ an inch. If the lever A :=: 36 inches, then the 

 circle described by its end a will be about 226 inches or 

 452 half inches; therefore one pound at « will balance a 

 resistance of 452 pounds, [Note. Since the lever m 36 

 inches, the diameter of the circle will be 72 inches, and the 

 circumference of a circle is 3.1416 times the diameter, there- 

 fore, 72x3.1416 z=L the circumference z=z 226 inches or 452 

 half inches.] 



LESSON 23. 



Pressure of Fluids. — In the vessel A B, Jig. 25. Engr. 

 II. the bottom C B does not sustain a pressure equal to the 

 quantity of the whole fluid, but only of a column, whose base 

 is C B, and height C F. In the vessel F G,/^. 24. the bot- 

 tom sustains a pressure equal to what it would if the vessel 

 were as wide at the top as bottom. If to the wide vessel 

 A B, Jig. 23. a tube C D be attached, and water poured into 

 either of them, it will stand at the same height in both ; of 

 course the small quantity in C D balances the large quantity 

 in A B. This has been called the hydro statical paradox, 

 because any quantity, hoicevcr small, may be made to coun- 

 terpoise any quantity, however large, but it is no paradox, when 

 we consider that the particles of a fluid press against each 

 other in every direction, not only downwards, but upwards 

 and sideways. 



