1317 
outline of the pulley 18 is such, that the trolley is drawn on with 
a speed of 1 mm. per minute. 
[It is essential, that the lever, in which T, turns, is kept steadily 
in the required position. Therefore after every movement it shoots 
behind an elastic pawl. Consequently the solenoids S, and S, must 
possess great strength in order to draw the lever back along 
the pawl. The electric current yielded by the battery could not 
perform this, and therefore use has been made for this arrangement 
of the alternate current of 220 Volt taken from the plug-switch SC. 
The circuits IV and V (drawn as an undulating line in the illus- 
tration) carry the alternate current. Mr. Mrssias invented an arran- 
gement, which prevented the current to pass longer than strictly 
necessary. In fact, the vertical shaft, to which the cores of soft 
iron are fixed in S, and S,, ends on both sides in a bone tip and 
this breaks the current in a gold-contact when the extreme position 
is reached. (This is not indicated in the picture). 
VII. Lhe tracing-pencil. The tracing is done in recording-ink i.e. 
with red, because the common lilae ink is not well reproduced in an 
ordinary photograph. The glass needles are made according to a 
model, used in the Royal Dutch Metereological Institute at De Bilt’). 
Every needle consists of a bulb, (capable of containing ink enough 
for recording during 48 hours), from which issues a pointed capil- 
lary tube, which rests on the paper. This tube is fixed to the bulb 
with the aid of sealing-wax. The whole is seized in a small clamp 
at the end of the shaft of the trolley. 
IX. The recording-drum revolves in 24 hours and has an outline of 
72 ems. Each hour is therefore 3 cms. and the minutes of 4 mm. 
are easily read. For paper millimeter-paper is used, so that after- 
wards a scale has not to be added and the data can immediately 
be accurately read. The paper is fastened round the drum by means 
of narrow brass hoops. 
The lines, written by the pencil when the trolley is drawn on 
by the clockwork U,, form an angle with the ordinate, the tangent 
of which is: the quotient of the distance, travelled by the recording- 
drum in one minute and that which the trolley travels along its 
rail in one minute, or >. 
As has already been mentioned above, the trolley is stopped after 
having run for 15 minutes. The clockwork need not stop, because 
the shaft of T, turns with friction. During that time the pencil 
writes a line parallel to the abscis (see fig. 2 and 3). 
5 Dr. C. ScHoure, Director of the Institute, was kind enough to explain this 
method to me. 
