1305 
replace the person, who works a similar non-recording apparatus. 
In the simplest case his work consists in the reading and recording 
the position of a hand and of a time designer (e.p. aneroid-barometer 
and barograph). With the porometer of Darwin and Pertz however 
the working of the apparatus is more complicated, for besides the fact 
that for each observation two positions and two moments have to be 
read and recorded, the apparatus has to be brought into its original 
position after each observation. So there are several functions here, 
which will have to be done automatically by. a selfrecording poro- 
meter. In constructing the automatic apparatus I have tried to keep 
the principle of the original porometer unaltered as far as possible. 
The apparatus (see fig. 1 lower half) consists of a glass chamber 
cemented to the leaf (1) [provided with the side-tube (2) indicated 
by VAN SLOGTEREN *), which must for the present be considered closed, 
just as the tube 18 in fig. 1], connected with a U-shaped manometer, 
with distilled water. The closed limb M, has a side-tube with rubber 
tube (8). In the case of the ordinary porometer the observer would, 
in bringing about a certain pressure, push open the elastic clamp-cock 
suck at the rubber tube and then let the elastic clamp recoil. In 
this case however the rubber tube leads to the water-jet-air-pump 
(P) and passes a compression cock, which as a rule closes it, but 
at the required moments is pulled open by an electro-magnet K,, 
so that the connection between air-pump and porometer is brought 
about. When the required air-rarefaction has been attained, the 
current of the magnet is broken, the clamp recoils and the rare- 
faction can only be adjusted via the stomata. 
Since the air-pump works continuously a very great rarefaction 
would soon arise in the space outside the cock, which on opening 
the cock would also appear in the porometer. To prevent this, the 
tube leading from the air-pump is branched outside the cock and 
a second rubber tube (4) runs between the movable part (5) of the 
cock and a fixed metal block (6). 
In the position of rest of the cock, this rubber tube is open and 
connects the pump with the atmosphere (at 7). When however the 
cock is pulled open, 4 is closed off, so that now the pump can 
only work on the porometer (through 3). So the water-jet-air-pump 
and the electro-magnetic clamp replace the sucking with the mouth 
and the clamp cock of the ordinary porometer. 6 
Now it should be looked to, that the electro-magnet works at the 
right time. The open limb M, of the manometer is wider than M, 
Wte p: 1S. 
84 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
