Fe ee 
1905] BRIEFER ARTICLES 147 
and vary not over one-thousandth of this weight from one another. These 
feed by gravity, one at a time, into a simple releasing valve, so arranged 
that when acted on by an electro-magnet a slide rises and allows one ball 
to drop through a tube into a scale pan, a new ball immediately taking its 
place in the releaser-slide. Attached to the releaser-slide is a bar carrving 
a pen, so adjusted that every time the slide moves, that is, every time a 
ball is dropped, the pen makes a vertical fine line with chronographic ink 
upon a record paper attached to a revolving drum. In use the plant to 
be studied is prepared in the manner usual for transpiration studies, and 
is balanced on a scale pan of any good balance, while the transpirometer 
is adjusted beside it. As the plant loses water this pan rises, and at the 
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top of its swing is made to touch a wire, thus closing an electric circuit; 
this excites the electro-magnet, which then raises the releaser-slide, drop- 
ping a ball into the scale pan (which is immediately depressed, breaking 
the circuit), and making a mark on the record paper. This operation is 
repeated thereafter every time the plant has lost a gram of water. The 
drum revolves once in twenty-four hours, and the record paper, a reduced 
copy of which is presented in the accompanying jig. 2, is divided into 
numbered spaces corresponding to the hours; these spaces are subdivided 
into twelve parts, each therefore representing five minutes,? and these in 
turn can easily be read by estimation to fifths, or one-minute intervals. 
It is possible, therefore, to read off from the drum directly the number of 
minutes it takes the plant to lose one gram of water, data which are readily 
transformable into other terms. The record paper is divided into seven 
horizontal spaces, marked by initial letters, one for each day of the week. 
The pen slides on the bar, which contains seven notches; and each day, 
when the plant is watered and the clockwork is wound, the pen is slipped 
along the bar one notch. Each record paper therefore contains a complete 
att five-minute spaces are exactly 1mm broad; hence millimeter cross-section 
Paper may be used instead of the record paper. This happened to be the case at the 
time the photograph (fig. 1) was made. 
