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formed, for if liquid is driven from the reservoir into the plant, it 
is replaced by the mercury which flows off over the open leg of 
the U-shaped tube. So in this apparatus there is neither a falling 
nor a rising column of mercury; the lower level of the column of 
mercury being always equal with the upper edge of the open leg 
of the U-shaped tube. The volume of the overflowing mercury is 
equal to that of the water driven into the plant; this mercury can 
be drawn off and measured at any time. These are the principles 
on which the apparatus is founded. 
I shall now pass on to a brief description of the various parts, 
for which I wish to refer the reader to the plate added to this 
paper, and in the first place to ask his attention for fig. A. At the 
top on the right side at 1 is the mercury reservoir which can be 
placed at different heights. It is arranged as wil] be seen like a flask 
of MARIOTTE, so that on the level a there is always atmospherical 
pressure. The tube b fits on the neck of the reservoir as a stopper 
and to secure it better is closed wich mercury. 
The mercury flowing from the reservoir passes through an india- 
rubber tube (2), with a wall-thickness of 2,5 mm. and a lumen of 
the same diameter, to the water-reservoir 3, to which also the plant 
is attached. Into this the mercury enters through the U-shaped tube 
c which possesses a glass tap d outside the reservoir. When the 
plant takes in water out of the reservoir 3, an equal volume of 
mercury will flow at e over the edge of the open leg of the U-shaped 
tube, and collect at the bottom of the reservoir 3. So the lower level 
of the pressing column of mercury is always in the plane ee’ and 
the distance ae, to be regulated arbitrarily, indicates the constant 
pressure under which water or any other liquid is driven into the plant. 
Three tubes more are attached to the water-reservoir 3: 
1°. the tube f leading to the plant; this tube is fixed high on 
to the reservoir, to let this contain as much mercury as possible thus the 
necessity of frequently drawing off the mercury being avoided. However, 
the tube soon bends downwards, passing into an open horizontal end. 
By this arrangement joining-pieces of simple shape can be used at 
g into which nevertheless the plant can be easily fixed with its 
plane of section in the level ee’. The connection at g is formed by 
means of the same thick-walled kind of india-rubber tube, which 
draws the mercury from the upper reservoir. This tube is so firm, 
and the surface upon which the pressure operates is so small, that 
even with a pressure of a full atmosphere the expansion is not of 
the slightest importance. The joining-pieces may have any shape, 
