Anderson: registering BALANCE. 179 



The armature having a recess to correspond with this para- 

 boloid, is placed between the two sides of the frame, being 

 pivoted at one end; the other end has a lever communicating 

 with the weight dropping mechanism by a connecting link. 

 This construction of the magnet gives a double magnetic cir- 

 cuit of low resistance, and also a maximum pull and greater 

 range of movement of the armature. The current from a sin- 

 gle good carbon-zinc cell is sufficient to operate the weight 

 dropping mechanism. The current from the battery passes 

 through the magnet to a mercury cup, thence through a pla- 

 tinum contact point on the scale beam to the binding post on 

 the case and back to the battery. 



The case is twelve by eighteen inches and is made of ena- 

 melled sheet iron riveted to a frame work of wrought iron. The 

 edges of the sheet iron are turned in so as to make with the 

 frame work a groove on each side for two sliding glass doors. 

 Thus the whole inside of the registering balance can be seen 

 and watched from without, and either side of the case opened 

 as desired. The case is leveled by means of four milled headed 

 brass screws. A circular spirit level is placed on the iron 

 plate immediately in front of the scale beam supports and thus 

 the entire apparatus can be leveled in a few moments. The 

 whole case is made so that it can be used in a green-house or 

 in the open air without interference from moisture or rain. 



The registering balance can be used for registering any con- 

 tinuous increase in weight. For transpiration a combined 

 calcium chloride and sulphuric acid absorber is placed on one 

 scale pan, and the previously dried air that takes up the trans- 

 pired moisture from the plant chamber (bell glass) is forced 

 through the absorber by means of an aspirator. Two light 

 pieces of rubber tubing connect the absorber with the plant 

 chamber and aspirator, by means of pieces of glass tubing in 

 rubber stoppers fitted into the case. The rubber tubes are 

 thus inside of the case and can not be disturbed by any outward 

 influence. They buoy up and down with the scale pan and 

 absorber. In balancing the scale for the beginning of an ex- 

 periment these pieces of rubber tubing are partly weighed and 

 continue to be a part of the weight on the absorber pan, but as 

 their weight is approximately constant no error results. 



An attachment is made to the balance when used for weigh- 

 ing large fruits, which necessarily must be grown outside of 

 the case. This is made by elongating the scale pan support to 



