158
He well understood that the Earth’s weather and climate are strictly dependent on
the Sun’s activity (Secchi 1863), as well as bearing a close correlation with the
nature of the geomagnetic field.
9.3.2 A New Hailstone Formation Theory
Inspired in part by the report of a sudden and very violent “aerial vortex” (Secchi
1876: 1–2) that the balloonist Madame Louise Poitevin (1819–1908) had experienced at an altitude of about 1200 meters above sea level, so strong that in less than
five minutes a bowl of water froze, Father Secchi became very interested in the
formation of hail. As a physicist, Secchi applied the new laws of dynamics and
thermodynamics to this study.
At that time there were different hypotheses on the subject. The prevailing theory, advanced by the authoritative physicist Alessandro Volta (1745–1827) in the
early nineteenth century, proposed an electrical origin for hail. But Secchi’s explanation was the first to be based on the laws of atmospheric dynamics and thermodynamics. For him, the role played by atmospheric electricity in the formation and fall
of hail was secondary; instead, latent heat played the leading role (Secchi 1876).
He connected the origin of this icy precipitation with the rapid whirling motion
generated by ascending warm air currents and obliquely descending colder ones
coming from the upper atmospheric layers. According to him, geographical conditions favorable to the formation of hail would be the presence of a large overheated
plain and a mountain system immediately adjacent to it. The repeated ascending and
descending motions within the vortex would lead to the freezing of water vapor in
the form of ice crystals (in the upper part of the thundercloud) which, transported
upward and downward by convective motions, would grow by overlapping new layers, alternately opaque and transparent. Father Secchi pointed out that most grains
would follow the strongest gusts of wind connected to “whirlwinds” with a predominately horizontal axis, thus falling on narrow and irregularly distributed bands.
9.3.3 The Urban Heat Island and Climate Change
Angelo Secchi was concerned with the well-being of the citizens of Rome, where he
spent most of his life. His studies were summarized in two remarkable lectures
given at the Accademia degli Arcadi, in 1865 and 1866.
In a booklet on the sanitary conditions of Rome (Secchi 1865), he underscored
how its climate is favorable for its people and for agricultural activity:
The climate of Rome is […] excellent and privileged by nature. The robustness of its citizens, their attractiveness and their very flowery color in winter, is enough to say that it is the
healthiest in the world. Foreigners know it and they […] spend the cold season there. Its sky
is proverbially bright, the temperature is moderate, extreme cold is unknown in winter […].
L. Iafrate and M. C. Beltrano
He well understood that the Earth’s weather and climate are strictly dependent on
the Sun’s activity (Secchi 1863), as well as bearing a close correlation with the
nature of the geomagnetic field.
9.3.2 A New Hailstone Formation Theory
Inspired in part by the report of a sudden and very violent “aerial vortex” (Secchi
1876: 1–2) that the balloonist Madame Louise Poitevin (1819–1908) had experienced at an altitude of about 1200 meters above sea level, so strong that in less than
five minutes a bowl of water froze, Father Secchi became very interested in the
formation of hail. As a physicist, Secchi applied the new laws of dynamics and
thermodynamics to this study.
At that time there were different hypotheses on the subject. The prevailing theory, advanced by the authoritative physicist Alessandro Volta (1745–1827) in the
early nineteenth century, proposed an electrical origin for hail. But Secchi’s explanation was the first to be based on the laws of atmospheric dynamics and thermodynamics. For him, the role played by atmospheric electricity in the formation and fall
of hail was secondary; instead, latent heat played the leading role (Secchi 1876).
He connected the origin of this icy precipitation with the rapid whirling motion
generated by ascending warm air currents and obliquely descending colder ones
coming from the upper atmospheric layers. According to him, geographical conditions favorable to the formation of hail would be the presence of a large overheated
plain and a mountain system immediately adjacent to it. The repeated ascending and
descending motions within the vortex would lead to the freezing of water vapor in
the form of ice crystals (in the upper part of the thundercloud) which, transported
upward and downward by convective motions, would grow by overlapping new layers, alternately opaque and transparent. Father Secchi pointed out that most grains
would follow the strongest gusts of wind connected to “whirlwinds” with a predominately horizontal axis, thus falling on narrow and irregularly distributed bands.
9.3.3 The Urban Heat Island and Climate Change
Angelo Secchi was concerned with the well-being of the citizens of Rome, where he
spent most of his life. His studies were summarized in two remarkable lectures
given at the Accademia degli Arcadi, in 1865 and 1866.
In a booklet on the sanitary conditions of Rome (Secchi 1865), he underscored
how its climate is favorable for its people and for agricultural activity:
The climate of Rome is […] excellent and privileged by nature. The robustness of its citizens, their attractiveness and their very flowery color in winter, is enough to say that it is the
healthiest in the world. Foreigners know it and they […] spend the cold season there. Its sky
is proverbially bright, the temperature is moderate, extreme cold is unknown in winter […].
L. Iafrate and M. C. Beltrano