RIEHL'S AUTOGRAPHIC APPARATUS. 231 



load. But in the case of ductile metals the actual breaking 

 load is usually less than the maximum. It is between these 

 two points that the local contraction is taking place, and 

 the load-strain curve shows a turning backwards at this 

 point, the load decreasing as the extension goes on rapidly 

 increasing. It is when this period is reached that there is 

 some difficulty in manipulating the poise Aveight so as to 

 keep the beam floating until fracture takes place. As soon 

 as the local contraction sets in the speed of extension 

 begins to increase rapidly, and it requires a considerable 

 amount of skill and quickness to run the weight back 

 quickly enough to keep the beam floating. If the beam 

 can be kept floating until fracture does take place, the 

 diagram produced by the present apparatus w r ill be correct 

 and satisfactory except for the effect of backlash, but if 

 the operator is unable to prevent the beam from falling on 

 to its lower stop, the diagram will be incomplete. What 

 has be.en said on this point also applies to other machines 

 which depend for their load indications on the movement 

 of the poise-weight. 



In the somewhat similar apparatus of Professor Hele- 

 Shaw, instead of the drum motion being taken from the 

 weight through the screw gearing, the motion is taken direct 

 by means of an endless band connected direct to the poise 

 weight and passing over guide pulleys. Mr. Aspinall's 

 arrangement is very similar. 



128. Richie's Autographic Apparatus. On Fig. 109 is 

 shown a general view of one of Messrs. Riehle' Bros, standard 

 machines (capacity 100,000 Ib.) fitted with automatic con- 

 trolling apparatus and autographic gear. The automatic 

 apparatus constitutes the arrangement whereby the position 

 01 the poise-weight is controlled automatically. At the 

 outer end of the beam are two electrical contact points, 

 so arranged that when the beam rises to its highest position 

 the points come into contact. The effect of this contact 

 is to complete the circuit of a current provided by means 

 of a battery of two cells. When this circuit is completed, 

 the armature of a magnet is attracted, and this puts the 

 screw controlling the poise-weight in gear with the driving 

 mechanism of the machine, and the weight is carried out- 

 wards towards the end of the beam. As the load on the 

 specimen is in this way increased, a further extension 

 takes place, the beam again falls, and the contact is broken. 

 The straining mechanism continues to pull on the lower end 



