W. Neilson Jones. 
3 62 
recording porometer: a similar record is made when the index 
reaches the terminals t't'. 
The rate of water loss is determined by the distance between 
these two records on the recording drum. 
If the index continues to pass up the tube BB', it reaches the 
wider portion B' A' where it collects in a globule and the water is 
drawn past it: the mercury therefore cannot be drawn out of the 
tube ABB' A '. 
If now the tube EE' is pulled vertically upwards so as to 
stretch still further the rubber tubing connecting F and C, the wider 
portion of the end E' is withdrawn from contact with the rubber 
cork closing C'. The drawn out portion of the tube, fitting loosely 
in the hole in the cork, serves as a guide to keep the tube EE 1 
straight, but allows through communication between the tubes EE' 
or BA and the tube CC '. 
The water current flowing to the transpiring branch passes now 
along the course EE' C'DGH since by this route the necessity is 
avoided of moving and supporting the mercury index. 
The mercury index meanwhile, being no longer supported by 
the “ pull ” of the transpiring branch, falls down the inclined tube B' B 
until it reaches the lowest point B. 
On allowing the tube EE' to return to its original position, the 
valve at C' closes and the mercury index once more passes up the 
tube BB' , recording its passage as described. 
Briefly—in order to cause the mercury index to return to B 
after it has run its course towards B', it is only necessary to 
momentarily open the valve at C by exerting a slight pull upwards 
on the tube EE'. 
There remains to be described the automatic arrangement for 
effecting this object. 
4. The Electrical Control. A sufficiently powerful electro¬ 
magnet M is fixed in the position shown, the tube EE' passing 
through a hole in the iron plate connecting the two bobbins at the 
top. 
The iron plate P, which forms the armature of this magnet, has 
an opening in the centre to permit the passage of the tube EE' and 
is fixed firmly to it by means of a collar 0 and a rubber cork Q. 
Thus, when a current passes through the magnet M, the tube 
EE' is drawn upwards and the valve at C opened. The terminals 
mm' of the magnet M are joined up to a battery of several cells Z 
and a relay R' is inserted in the circuit. This relay R' and also the 
