History Forum / General / General Topics / September 2007

Hi Toady,

It's difficult to see in the small picture online, but there are
two mousetraps in the picture: the one on the table is 'armed'
and the one on the windowsill in the background is 'at rest'.  

How do they work?  I could draw this to show you, much
easier than trying to describe it with words, but here's how
they worked:  

What's difficult to see about the one on the table is that
there is a slab extending at a downward slope, almost
directly away from the viewer, from the upraised crossbar
to the rear edge of the base of the contraption.  Campin's
technique renders the slab almost invisible, and one wonders
whether he did it to prove his mastery of perspective, or to
theologically minimize the importance of the device's lethal
purpose, since it obviously represents Jesus.  

The slab would have been brick or stone in these models,
because they are not very thick.  If it was wooden, it would
be much larger to get the necessary weight, heavy enough
to crush a mouse.  

Between the upright arms which support the crossbar, a pin
is inserted to support the slab.  The lower end of the pin rests
on a movable piece of wood directly below the crossbar.  
The skill factor comes into play here.  The lower sill must
contact the trigger, but also be free to move.  Then you
must try to balance the pin on top of it as precariously as
you can, while still supporting the weight of the slab.  

The ridge you see along the base serves two purposes.  
First, it helps to stabilize the slab when setting the trap.  
Second, it provides another few milliseconds of indecision
in the mouse's brain, greatly improving the trap's value.  

Below the loose piece of wood, a curved piece is inserted
with the ends pointing upwards... one end thick and the
other one, thinner and pointy, on the inside of the trap.  
This is the trigger.  

What looks like a keyhole in the base in your image is actually
the left edge of the thicker end of this curved piece, facing
outward.  Campin was pretty good at perspective, but he still
had issues with visualizing light sources.  The leftmost panel
in this triptych has a shadow pattern with the light emanating
from the central panel, the Annunciation.  

The rightmost panel of Joseph has two light sources: an
emanation from the central panel as reflected in the tools,
and another source from the open shutters.  For his reasons,
Campin chose to shadow everything above the mousetrap
as illuminated by the windows.  So what did he do at the
border between these two light sources?  He places the
main mousetrap and a small bowl.  Follow that horizontal
line across Joseph's chest.  Everything above is lit by
window, everything below is lit by the Annunciation.  

The bowl and his clothes are smoothly lit from both lights,
but the mousetrap is lit unevenly, with some parts reflecting
only from the windows, and other parts only reflecting light
from the central panel.  The face of the mousetrap's base
which shows towards the viewer is shadowed by light
through the windows, but the higher crossbar is shadowed
as if lit from the central panel of the triptych.  

This is why it looks like there is a hole in the base of the
trap.  Rather, this is the thick end of the curved trigger,
with a mistake in shadowing, either unintended by Campin
or by design to emphasize the mysticality of the device.  

The pointy end of the trigger is behind the pin in this image,
directly under the slab.  The pointy end is to secure the bait,
to make the mouse work hard to get it.  It's curved to ensure
that moving the thinner end will disturb the thicker end.  

The idea is that when jostling the bait, the mouse jiggles
the curved piece, which then dislodges the free piece of
wood supporting the lower end of the pin.  As soon as
that moves, the pin flies out and the slab comes down,
crushing the mouse.  

Why is the trigger curved?  So it doesn't break when the
slab crashes down, and also to minimize the space it allows
between the slab and the base.  The outward end pivots
upward when the slab crashes down, so you don't have
to replace the trigger every time you smoosh a rodent.  

The pin has an eyelet at the top to attach a string.  
When the trap springs, the pin will fly out.  If you don't
want to spend fifteen minutes fishing the pin out from
under a cupboard, you tie a string to it.  In fact, this
design won't work if a string is not suspending the
pin from above.  As the slab comes down, it pushes
the string outward, ensuring that the pin flies outward.  

Without a string, or with a string attached to any other
place, the pin will fall inwards half the time, allowing the
mouse some wiggle room and a half-caught mouse will
have a chance to survive.  

This is why the upright arms and crossbar are
necessary: the pin must fly outwards or it's now
a mousescarer, not a mousetrapper.  

Why is the base sloped in a wedge shape?  That
decreases the distance the slab must travel, and
so decreases the time that an alert mouse has to
escape.  It's a game of milliseconds.  

For the same reason, the triggers on both mousetraps
in this image are on the right side of the mechanism.  
It was meant to be placed along a wall with the trigger
close in, blocking off the victim's quickest exit route.  

This website has a short video of a similar mousetrap
in operation.  This one uses a brick as the slab, and
clearly has forgotten some useful design elements
which the Dutch knew about in the early 1400's...  

http://youtube.com/watch?v=HmvMEyyStYM

As for the explanation of the presence of a mousetrap in
Joseph's workshop, the page you link to does a good job
of relating Joseph's religious role in producing God's Cosmic
Deviltrap.  But this image is full of other double-meanings...  

The upper mousetrap (outside the house) is already sprung
and the one on the table is ready to go.  This expresses the
idea that Jesus is forever protecting the faithful, but mankind
must toil to keep their spiritual defenses ready.  This attitude
was a key philosophy in the European executions of witches
at the time it was painted.  

Note Campin's crafty use of perspective in placing the
mousetrap on the windowsill... look just above it and see
the relative size of the people in the city square.  The
mousetrap would be the size of a gallows sitting in the
square, and Campin has adjusted the position of the
upright arms and crossbar to reinforce this impression.  

The theological double-entendre is clear.  The same trap
that snares the devil is also the basis for justice in a good
god-fearing society.  What undoes the devil also spells
doom for the townsfolk who the devil himself has snared.  

Remember the string hanging down on the upper mousetrap?  
As a gallows, this is the noose.  As a mousetrap, this is the
technological innovation that ensures the mouse's demise.  
The two meanings are that man's laws reflect god's laws,
and that mankind is expected to fight the devil, using Jesus
(the vigilant mousetrap on the table) as an example.  

Joseph is making a sieve, but over the arm of his bench, not
on the table next to the mousetrap.  Thus leaning to his left,
Joseph is out of the arc of the shutters precariously suspended
from the ceiling.  If the shutter (slab?) above him should fall,
Joseph is safe.  The double-entendre about Joseph's posture
is that divine protection is bestowed to Joseph because he is
making an object which separates the good from the bad...
and that he is blessed because he separates his pious work
on God's Cosmic Mousetrap from his daily carpentry tasks.  

I know it sounds goofy, but in the early 1400's this was meaty
stuff!  In those days, all European art was religious.  The only
measure of creative expression a Dutch artist of the early
1400's could show was in the level of cleverness he could
inject while depicting biblical scenes.  

Hope that answers your question about the trap (and the painting)  

SL