33 



tip. These are intended to direct the 'line through the 

 ring at the summit, so as to make it keep close to the rod 

 all the way (whereby it is not allowed to hang about in a 

 loose manner), and to give to every part a due bend. 



The rings should be rather numerous than scanty, espe- 

 cially on the thinner parts ; for, the closer the line is kept, 

 the greater are the angles it makes between any two con- 

 tiguous rings, and consequently, the more equable is die 

 bend throughout every part of the arch described by a 

 rod when in a state of exertion. 



When the rings are too distant, they frequently tear 

 out, or the rod snaps in the too long interval between 

 them, which rs thus obliged to bear more than its due 

 proportion of the stress. 



The following scale will, perhaps, be found as good a* 

 any that can be devised. Place your first ring at two 

 inches and a half from that on the tip of the rod. Now 

 the inches on most rulers being divided into eight equal- 

 parts, in the above distance there will be twenty equal 

 spaces, each equal to the eighth of an inch. 



Let every succeeding space be increased by the addition 

 of one- fifth of the measure of its preceding interval. 



Thus, the uppermost interval being twenty-eighths, 

 one -fifth of that added to itself, will give twenty- four 

 eighths (i. e. three inches) for the second interval. 



Then, for the third interval, take twenty-four eighths, 

 and its fifth, which is nearly five-eighths, and its measure- 

 ment will be about twenty- nine eighths, or something 

 jnore than three inches and a half. 



The fourth interval will be twenty-nine, added to its- 

 fifth, say six-eighths, which give a total of three inches 

 jind three-eighths* 



c 5 This. 



