THE YOUNG FAKMER's MANUAL. 445 



697. There have been of late several patent improvements in 

 squares and measuring rules. But I shall notice none of them 

 except the one in which the blade of a common hand-saw is 

 graduated on both sides, atnts back edge. There can be no par 

 ticular objection to this manner of having a measuring rule. 

 But they who use this kind only, will find it, many times, 

 very inconvenient ; and, besides, the teeth of the saw would be 

 very liable to get a dulling oftener than we like to file them, and 

 it makes an awkward, clumsy rule at best. A saw and a good 

 carpenters' square cannot very well be judiciously and conven 

 iently combined. 



698. For measuring the circumference of anything, or the out 

 side or inside of the rim of a wheel, or drum, it is not very prac 

 ticable to do it with a straight rule. For such purposes a meas 

 uring wheel is made use of, which is represented by Fig. 188. 



FIG. 188. 



A MEASURING WHBBL. 



The wheel should be about six or eight inches in diameter, and 

 instead of being flat on the surface of the circumference, the 

 wheel at the circumference should be formed to a sharp edge 

 entirely around it. If it is three or four eighths wide at the cir 

 cumference, it is much more liable to vary from the correct meas 

 urement of anything which is measured with it. In measuring 

 with the wheel, the operator must be careful to have it roll in a 

 straight direction, and not from right to left, as that would indi 

 cate a greater distance than it really is. 



