100 MECHANICS. 



Fig. 85. 



'n: 



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1 



^5 ^ ^ 



The first is equally strong with the second, and much 

 lighter.* The same form doubled must be given if 

 the bar is supported at the middle, with a weight at 

 each end, or with the weight at the middle, supported 

 at each end, as c. This form, therefore, is a proper 

 one for many parts of implements, as the bars of whip- 

 pie trees, the rounds of ladders, string-pieces of bridges, 

 and any cross-beams for supporting weights. One 

 half of this form, as a, is the proper form for rake- 

 teeth, wheel-barrow handles, spade handles, &o. On 

 fence-posts, the pressure being nearly alike on all parts, 

 they should be nearly in the form of a wedge. There- 

 fore a post of equal size throughout contains nearly 

 twice as much timber as is needed for strength only. 



The form of these parts must, however, be modified 

 to suit circumstances ; as whipple-trees must be large 

 enough at the ends to receive the iron hooks, wagon- 



* The simple style of this work precludes an explanation of the 

 mode of calculation for determining the exact form. Where the 

 stick tapers only on one side, it is a common parabola ; if on all 

 sides, a cubic parabola. 



