1911.] 



The Stomatograph. 



39 



50 metres away, and connected with the binding-screws from the relay by 

 double flexible wiring. 



The Marker. — This (p) was simply a single-beat electric bell, bearing a pen 

 in place of the hammer, and so marking a vertical dash across its trail on the 

 drum whenever the circuit was closed and broken. 



The Battery. — A single " W.-O." cell was amply powerful for this circuit. 

 The Drum. — The drum was required to differentiate between marks made 

 at intervals of only 5 seconds, and to record for 30 hours continuously. 

 A vertical chronograph was therefore adopted, descending on a screw, with 

 one rotation of 15 cm. circumference in every hour. 



A brief note on its construction, which was remarkably cheap, may perhaps be 

 included. The proper screw was replaced by a spiral (sp) of stout brass wire, 

 extended to the requisite pitch, and fitted closely over a glass rod (r). The nut (n) 

 consisted of three needle-points, chocked to their correct relative heights round a hole 

 in the centre of a piece of tin, which clipped the lower end of the drum ; their points 

 bore on the central glass rod, and their lower sides on the brass wire. With the 

 screw-pitch and weight of drum employed, the clock (CI) was more nearly a brake 

 than a motor. 



The hour spindle of the clock was fitted with a double " L " piece, over the 

 upturned ends of which were dropped the lower ends of two vertical glass tubes 

 (g, g). These passed upwards, parallel with the screw-axis and inside the drum, 

 through two guide holes in the tin nut, and then through two more in the top 

 cover (c) of the drum, which was thus free to move vertically down these two 

 driving rods, though constrained to a spiral motion by the screw. 



A retort-stand served to hold the axial screw, and a cheap American clock, placed 

 centrally beneath it, drove the drum. The timing was corrected by marking the 

 time at the beginning and end of a record, and cutting the paper off the drum along 

 the hour-line. 



(f) The Chamber. — Some difficulty has been experienced by workers with 

 the porometer in the cementing of the leaf to the chamber. A method 

 devised by the writer appears to be an improvement, since a tight joint 

 can be made or broken in a few seconds, and may be maintained for 

 several days without direct injury to the leaf. The flange of the chamber 

 (fig. 3a) contains a deep groove, concentric with the chamber itself, this 



groove being filled to overflowing with paraffin of some melting-point 

 suitable to the particular circumstances, from 50° C. to 30° C. The wax 



A 



Fig. 3. 



