3£» 



Mr. I. Newton on an improved Cross. 431 



good deal of labour, I hope the following description of an 

 improved cross, lately invented by myself, as it is calculated 

 to abridge in a great measure the labour here complained of, 

 will not be found uninteresting to some of the readers of the 

 Philosophical Magazine. 



A B D G represents the upright staif, and C the cross fixed 

 at the upper end of a slight straight rod of wood F H, and 

 resting on an horizontal arm or 

 flat and straight piece of wood 

 E B F, having two circular holes 

 at B and F, large enough through 

 which to admit the staff and rod 

 at right angles to the arm ; which ^ 

 arm is moveable about the staff, 

 and may revolve about it at plea- 

 sure. A E D is a small spring or 

 bent piece of iron, capping the 

 arm at E, where, being riveted, it 

 presses on the staff at A and D, 

 above and below the arm, and 

 serves to adjust the arm to any 

 height on the staff, and to keep 

 the arm in any required horizontal 

 direction. The rod F H being 

 fixed to the cross at F, and paral- 

 lel to the staff, and also free to 

 turn in the hole at F, answers a 

 threefold use ; as it keeps the cross 

 on the arm, turns the sights in any 

 direction, and points out where, 

 on the ground, the chain must fall. In practice I think it will 

 be found most convenient to have the radius or part of the arm 

 B F about 1 8 inches long, and the rod F H about 3 feet and 

 a half in length. 



In measuring diagonals, &c. by means of the chain and 

 common cross, the young practitioner is frequently obliged to 

 prick his staff in six or seven different places before he can 

 succeed in finding the diagonal, &c. ; but in using the above, 

 he will seldom find it requisite to ground his staff more than 

 once, in order to answer the same purpose. For instance, 

 having brought his cross as near to the diagonal, &;c. as he can 

 guess, the error, if any there be, may easily be corrected by 

 tiie radius B F, which, as before observed, is made to revolve 

 about the staff. I remain, sir, youi'Sj &c. 



WUbecli, June K, 1825. Isaac NewTON. 



P. S. 



