1911.] 



The Stomatograph. 



43 



addition the most direct relation to irrigation matters, which are of great 

 economic importance for Egypt. 



§ 4. Summary. 



The stomatograph is an air-pump measuring and recording the quantity of 

 air which it forces through a leaf on the chamber of Mr. Francis Darwin's- 

 porometer, and so recording any changes in stomatal aperture. 



It is extremely easy to use, and having been so constructed as to be 

 independent of weather changes, is specially adapted to obtaining records 

 from plants under normal out-door conditions of environment, such as are 

 required in agricultural and ecological studies. 



Eecords obtained in this way with the Egyptian cotton crop show that 

 the instrument may be of great utility in the study of purely economic 

 matters connected with irrigation. 



Apart from its use for the special purpose, the form of pump adopted 

 seems likely to be of use in replacing aspirators for many kinds of scientific 

 research. 



My thanks are due to Mr. Francis Darwin for the interest which he has 

 taken in this modification of his porometer, and to Mr. Horace Darwin for 

 suggestions as to its improvement. My colleague, Mr. Frank Hughes, is 

 responsible for many ideas, and for assistance in making the various working 

 models. 



DESCRIPTION OF THE FIGURES. 

 General : The drawings of apparatus are all semi-diagrammatic, sectional and super- 

 ficial views being combined in the same figure. Figure 4 is plotted from the chronograph 

 records. 



Fig. 1a. — Interior of case containing pump, relay, and battery. Gas-holder and solenoid 

 in section, remainder in diagrammatic view. Insulated wire represented by dotted 

 lines, or by spirals. Battery (CZ) is actually stored at the back of the case, behind 

 the pump. 



p. Pump nozzle for connection to chamber. 

 t, t. Telegraph connections to recording apparatus. 



a. End of rod which depresses the contact arm, Ca. 



b. End of similar rod which knocks off the contact arm. 



B. Pillar of balance, bearing quadrant beam in front, and contact arm behind 



on same pivot. 

 Ca. Contact arm, during contact. 

 Ca', Ca'. Normal position of contact arm. 



A. Light armature on contact arm. 



M. Holding down magnet, maintaining contact of Ca by means of A. 

 Br. Bracket supporting insulated fixed contact at tip. 



