ATMOMETKY AND THE AT.MOMETER 101 



mounting. As Harvey has suggested (loc. cit.), a stopcock 

 might replace valve D, though experience with too frequently 

 leaky cocks leads the writer to maintain that the mercury valve 

 is as simple as, and far more certain than any possible cock. 

 When the cup is to be removed it is simply lifted from its stopper 

 and the contained water is allowed to escape at random. A new 

 cup is placed on the stopper and suction is applied to tube F as 

 at first. 



To avoid possible disturbance of the valves and tubes at each 

 reading, they being attached to a support, a large mouth bottle 

 has been latterly employed, fitted with a tight and permanent 

 waxed cork stopper. This stopper is perforated for the tube E 

 and also bears a glass tube of large bore (about 1 cm.) and about 

 10 cm. long, reaching nearly through the cork from above. The 

 lower surface of the cork is reamed away to form a broadly coni- 

 cal opening to conduct air bubbles upward into the large tube. 

 This tube serves as does the small neck of the bottle in figure 5 

 and bears a file mark for the zero point. Still better, the large 

 tube may be graduated in cubic centimeters, thus making the 

 reading of small losses possible. The bottle is filled through this 

 tube by use of a small funnel. This arrangement is shown in a 

 diagram of the atmometer furnished by the writer, for publica- 

 tion by D. T. MacDougal. 22 The same arrangement is shown 

 in Shive's diagram, about to be mentioned, which is here repro- 

 duced, with its author's kind permission, as figure 7. 



Shive 23 has recently greatly improved the details of the non- 

 absorbing mounting so that no extra support is necessary and both 

 mercury valves (as bulbed glass tubes) are brought to lie within 

 the reservoir. The Shive arrangement seems practically per- 

 fect. It is shown in figure 8, which is self-explanatory. It is 

 to be noted that the suction tube here projects to the outside, 

 through the cork stopper, far enough for the attachment of a rub- 

 ber tube. Only mercury enough to give a column about 3 cm. 



22 MacDougal, D. T., The measure of environic factors and their biologic 

 effects. Pop. Sci. Monthly 84: 417-433, 1914. The diagram here mentioned is 

 on page 421, and was unfortunately inverted by mistake. It represents a spher- 

 ical porous cup. 



23 Shive, J. W. ■ 



