199
theory of small vortices [teoria de’ vorticetti]: anyway, this author seems to uselessly complicate the hypothesis with the assumption of the existence of certain
structures in the fluid....”
The reason for this lack of acknowledgment of Maxwell for his theory, which is
nowadays recognized as one of the milestones of physics, is that Secchi’s “unifying” concept was kinetic. In his view, every (microscopic or macroscopic) physical
phenomenon, including gravity, could be explained by the motion of its constituents. In this regard, in Chap. IV, page 5, he says: “In any event, gravity should not
be confused with light or heat because, although both arise from molecular agitation, they behave differently in the modification of the environment.” Appealing;
but wrong.
Secchi’s theory was not much different from Descartes’ theory of vortices. In
fact, Secchi’s reduction of gravity to kinetic theory required (as for the other forces)
a physical medium, i.e., the existence of a “luminiferous aether”, which would be
shown not to exist only in 1887, nine years after Secchi’s death, by the Michelson Morley experiment.
Another mistake lies in the statement that Secchi makes still in Chap. IV, page 5:
“…adding forza viva (i.e. kinetic energy) to a material system, corresponds to
increasing relative distances of its elements, by which we obtain as its sole effect a
reduction of gravity in a given space volume.” Why does he assert this? “Because,
if we heat a cube of dimension one meter, its volume will increase and a fraction of
its matter will be moved out of its original one meter size and so in that one meter
cube the mass (and gravity) will diminish.”
This is true on the Earth, where pressure is held constant, but not generally true.
However, in this case, he was not fully responsible for this error. It was only in 1870
(eight years before Secchi’s death) that Rudolf Clausius (1822–1888) proved the
virial theorem, which shows that a self-gravitating system in equilibrium (like our
Sun or a cluster of stars) can have a negative thermal capacity. This means that adding forza viva into the system, i.e., increasing its total energy, can have the result of
increasing potential energy but decreasing kinetic energy within the system. This
can be seen in the example of a satellite in orbit around a planet, where an addition
of energy brings it to a higher orbit, with more potential energy, but at a lower
speed – hence, kinetically speaking, a lower “temperature.”
Without going further into the details, we conclude this short note by admiring
the goal, if not the final conclusions, of this remarkable book from this great scientist. Even if some of the statements and theories therein were later shown to be
inadequate or incomplete, Secchi’s book nonetheless represented a formidable
attempt at a synthesis of the physical theories of his time.
Reference
Chinnici, I. (2019). Decoding the stars a biography of Anglo Secchi Jesuit and scientist. Leiden/
Boston: Brill.
11 Secchi’s Book on “The Unity of Physical Forces”
theory of small vortices [teoria de’ vorticetti]: anyway, this author seems to uselessly complicate the hypothesis with the assumption of the existence of certain
structures in the fluid....”
The reason for this lack of acknowledgment of Maxwell for his theory, which is
nowadays recognized as one of the milestones of physics, is that Secchi’s “unifying” concept was kinetic. In his view, every (microscopic or macroscopic) physical
phenomenon, including gravity, could be explained by the motion of its constituents. In this regard, in Chap. IV, page 5, he says: “In any event, gravity should not
be confused with light or heat because, although both arise from molecular agitation, they behave differently in the modification of the environment.” Appealing;
but wrong.
Secchi’s theory was not much different from Descartes’ theory of vortices. In
fact, Secchi’s reduction of gravity to kinetic theory required (as for the other forces)
a physical medium, i.e., the existence of a “luminiferous aether”, which would be
shown not to exist only in 1887, nine years after Secchi’s death, by the Michelson Morley experiment.
Another mistake lies in the statement that Secchi makes still in Chap. IV, page 5:
“…adding forza viva (i.e. kinetic energy) to a material system, corresponds to
increasing relative distances of its elements, by which we obtain as its sole effect a
reduction of gravity in a given space volume.” Why does he assert this? “Because,
if we heat a cube of dimension one meter, its volume will increase and a fraction of
its matter will be moved out of its original one meter size and so in that one meter
cube the mass (and gravity) will diminish.”
This is true on the Earth, where pressure is held constant, but not generally true.
However, in this case, he was not fully responsible for this error. It was only in 1870
(eight years before Secchi’s death) that Rudolf Clausius (1822–1888) proved the
virial theorem, which shows that a self-gravitating system in equilibrium (like our
Sun or a cluster of stars) can have a negative thermal capacity. This means that adding forza viva into the system, i.e., increasing its total energy, can have the result of
increasing potential energy but decreasing kinetic energy within the system. This
can be seen in the example of a satellite in orbit around a planet, where an addition
of energy brings it to a higher orbit, with more potential energy, but at a lower
speed – hence, kinetically speaking, a lower “temperature.”
Without going further into the details, we conclude this short note by admiring
the goal, if not the final conclusions, of this remarkable book from this great scientist. Even if some of the statements and theories therein were later shown to be
inadequate or incomplete, Secchi’s book nonetheless represented a formidable
attempt at a synthesis of the physical theories of his time.
Reference
Chinnici, I. (2019). Decoding the stars a biography of Anglo Secchi Jesuit and scientist. Leiden/
Boston: Brill.
11 Secchi’s Book on “The Unity of Physical Forces”