BOW THE TESTS WERE CONDUCTED. 19 



manner of using them, also the methods employed in calibrating 

 the springs, require notice. 



In nearly all the indicator work on the Corliss, and similar 

 types of slow-speed engines, the driving-rig has been some 

 form of pantagraph, and in the large majority of cases, that 

 form known as the " lazy-tongs," working horizontally and 

 operated from the cross-head. The fixed end of the lazy-tongs 

 has generally been applied to one of two wooden posts, attached 

 to a base-board, which in turn is fastened to the floor. The 

 second post, suitably located with reference to the first, is used 

 for the support of a carrier-pulley, and both posts are securely 

 fixed in position by means of three wooden braces fastened to 

 the floor. This method of attaching the lazy-tongs has the 

 advantage of rigidity, which is so essential to a correctly driven 

 indicator; and the use of the carrier-pulley enables the driving- 

 cord to be always led oft' in a line parallel to the direction of 

 motion of the cross-head, whatever the position of the indi- 

 cators with reference to the cord-pin of the lazy-tongs. The 

 construction of a stand for supporting the lazy-tongs in this 

 manner may be considered crude and clumsy for permanent 

 use ; but the author has often found permanent rigs defective 

 fmin improper design or insecurity, due to gradual wear, and 

 substituted the one described. Being made throughout of 

 wood, it is a device which can be quickly put together, even 

 where there is no carpenter-shop at hand and little material. 

 As it is built in such form as to easily and positively accom- 

 plish the desired ends, it has been found most useful. 



1 '>! a driving-cord, a strong braided linen fish-line having an 

 unbraided core is used, extending a little beyond the carrier- 

 pulley ; and from this point to the indicators, pieces of annealed 

 brass wire are used, about No. 25 B.W.G. ( 5 y in diameter). 

 Km- ;i single cylinder two cords are thus brought into use lead- 

 ing from the same initial point. In the case of tandem cylin- 

 ders, either four independent cords are used, or two independent 

 cords, each having branch loops at appropriate points for con- 

 necting to the two instruments. In some cases the cords have 

 been displaced by a light wooden rod driven by the cord pin of 



