Franklin and Le Roy: Report on Lightning Rods
at Strasbourg
als (draft): Académie royale des sciences, Paris
<May 12, 1780, in French: The Académie has asked us to report
on a memoir by M. Barbier on the means of arming the Strasbourg
cathedral with lightning rods.
Strasbourg is located in the middle of rather flat countryside
dominated by the cathedral’s very high spire—so high indeed
that no attempt at devising a protective system for so tall a building
has ever been made. Its exterior, furthermore, is studded
with a large number of iron bars and clamps which add to the
danger posed by the frequent storms. Those storms originate
southwest of the city, in the Vosges, and proceed in a northeasterly
direction.
The two crucial issues we shall discuss are the shape given to
the lightning rods’ ends and the means by which the lightning’s
fire is brought down to earth.
On the first question, M. Barbier wisely prefers the rods with
pointed ends and suggests that they be gilded so as to preserve
them from the weather, and also to create an effect pleasant to
the eye. As to the second problem, about which one cannot be
too cautious, it should be noted that the spire is divided into three
parts. Starting from the top, they are a tier made up of cross,
lantern, and crown; then a pyramid in the shape of an octagon
consisting of eight small winding stairs and turrets; and finally,
resting on the platform, a square construction flanked by an
openwork turret containing a staircase.
M. Barbier proposes, for the top part, a scaffolding of vertical
iron rods off the northeast and southwest sides—those most often
hit by storms—to join a “necklace” of horizontal rods just
below the crown. From this necklace there would jut four rods
descending between the little staircases of the pyramid and corresponding
to the four turrets. They would finally follow at a
distance the outer walls of the turrets belonging to the lowest
part, which rests on the platform.
Protruding from the long drop between the cross and the turrets,
a number of secondary conductors, five or six feet long and
ending in copper-covered joints, would have to be installed for
extra security. More of the same should be placed at each angle
of the platform.
One third of the way down between the platform and the
ground there runs a circular gallery, and more rods could be
placed there, as well as a protective system extending to the copper
roof of the nave. For better safety still, lead washers should
be inserted between the various screws.
The final step is to connect this protective framework to the
ground.
M. Barbier’s solution is to establish a tight metallic connection
between the copper roof of the Mitre and the three adjacent copper
roofs, two of which are well suited to attract lightning since
they are garnished with very pointed pyramids.
Such a system would provide excellent protection against
storms coming from the east. Since that part of the cathedral is
so far removed from the tower, M. Barbier plans to give it extra
safety by adding still sharper points to those of the pyramids.
The next step is to take advantage of the two gutters situated
right there, which can be made to communicate, through a
leaden pipe, with an already established well. As usual, there will
be a duplicate fallback system in case of accident, in the shape of
metal rods constructed in the same way as those in the front of
the cathedral. Both systems will be joined at the bottom by a
thick iron bar pushed at least one foot into the ground at the bottom
of the well.
Let us add, to complete this description, that M. Barbier proposes
to secure the rods by flattening their extremities as well as
those of the “necklace,” then drilling a hole through these flattened
parts and attaching them to each other by means of a
square-headed screw tightly shut by two keys.
It is our opinion that M. Barbier’s system would present still
greater security if the Mitre were provided with more points and
if the descending rods were made thicker. We agree with his observation
that the work should proceed from bottom to top. We
conclude by praising his plan and expressing the hope that, given
the disastrous history of Strasbourg’s tower, it will become a reality.
Thus protected, the tower will be a model for the rest of the
kingdom and a symbol of the progress accomplished by physics
in France when it is considered that only fifteen years ago lightning
rods were still viewed as dangerous.>
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