167
mation, and not only to Paris but to Florence and Petersburg, in addition to the dissemination of such meteorological data through the newspapers […]. (Secchi 1877: 45)
12
At the same time, Secchi received from Paris the corresponding values measured in
the other observation points of Le Verrier’s European international network. “The
observations collected by Le Verrier were then lithographed and sent back to the
observatories in the form of bulletins. Based on these bulletins the laws of storms
were studied at the Observatory” (ibid.).
13
Although Secchi knew well that basing storm forecasts on observations “recorded
in the bulletins […] only once a day, namely at 7 am,” limited their success, he tried
to use all the information he received to thoroughly investigate atmospheric perturbations and their main trajectories (Secchi 1858: 97–98). It was for this purpose that
he introduced the graphic method, which he considered as the “only one useful in
this matter.”
9.5.3 Isobars and Isotherms for Weather Forecasting
Angelo Secchi was a pioneer in introducing isobars and isotherms in the nascent
field of storm forecasting. Drawing on data recorded in the European stations of the
“International Meteorological Exchange,” he would record atmospheric pressure
and thermometric values measured simultaneously on unlabeled European maps
and connect the values of equal pressure and temperature by isobars and isotherms,
respectively. These constituted the first charts of surface pressure and temperature
to be used for weather forecasting; today they are the foundation of the entire edifice
of synoptic meteorology.
14
As soon as the pressure, temperature, and wind data recorded at the various
European observatories at the established synoptic time (7 or 8 in the morning,
depending on the season) and reported in Le Verrier’s international Bulletins arrived
at the Collegio Romano Observatory, they were represented on a large map of
Europe, 1 meter high and 1.25 meters wide, with 20 cm long rods protruding from
the location of each station. So, for instance, the base level of barometric pressure
was arbitrarily fixed at 730 mm of mercury (corresponding to 973.1 hPa). Each rod
was made to protrude by half a centimeter for each mm of pressure above this level,
so that its maximum protrusion would be 20 cm, corresponding to a value of 770 mm
12 Ogni mattina si spediva a Parigi il telegramma delle osservazioni fatte alle 7 antimeridiane colle
altre informazioni richieste, e si continua anche oggidì a spedirlo non sola a Parigi, ma a Firenze e
Pietroburgo, oltre alla diffusione dei listini meteorologici nei giornali, come si disse.
13 Le osservazioni raccolte dal Leverrier venivano poscia litografate e rinviate così raccolte agli
osservatorii. Fu su questi bullettini che all’osservatorio si studiarono da principio le leggi delle
burrasche.
14 The branch of meteorology that analyses meteorological observations carried out simultaneously
over a large area of the globe in order to forecast the short, medium, and long-term evolution of
weather.
9 Angelo Secchi and Meteorology in Italy
mation, and not only to Paris but to Florence and Petersburg, in addition to the dissemination of such meteorological data through the newspapers […]. (Secchi 1877: 45)
12
At the same time, Secchi received from Paris the corresponding values measured in
the other observation points of Le Verrier’s European international network. “The
observations collected by Le Verrier were then lithographed and sent back to the
observatories in the form of bulletins. Based on these bulletins the laws of storms
were studied at the Observatory” (ibid.).
13
Although Secchi knew well that basing storm forecasts on observations “recorded
in the bulletins […] only once a day, namely at 7 am,” limited their success, he tried
to use all the information he received to thoroughly investigate atmospheric perturbations and their main trajectories (Secchi 1858: 97–98). It was for this purpose that
he introduced the graphic method, which he considered as the “only one useful in
this matter.”
9.5.3 Isobars and Isotherms for Weather Forecasting
Angelo Secchi was a pioneer in introducing isobars and isotherms in the nascent
field of storm forecasting. Drawing on data recorded in the European stations of the
“International Meteorological Exchange,” he would record atmospheric pressure
and thermometric values measured simultaneously on unlabeled European maps
and connect the values of equal pressure and temperature by isobars and isotherms,
respectively. These constituted the first charts of surface pressure and temperature
to be used for weather forecasting; today they are the foundation of the entire edifice
of synoptic meteorology.
14
As soon as the pressure, temperature, and wind data recorded at the various
European observatories at the established synoptic time (7 or 8 in the morning,
depending on the season) and reported in Le Verrier’s international Bulletins arrived
at the Collegio Romano Observatory, they were represented on a large map of
Europe, 1 meter high and 1.25 meters wide, with 20 cm long rods protruding from
the location of each station. So, for instance, the base level of barometric pressure
was arbitrarily fixed at 730 mm of mercury (corresponding to 973.1 hPa). Each rod
was made to protrude by half a centimeter for each mm of pressure above this level,
so that its maximum protrusion would be 20 cm, corresponding to a value of 770 mm
12 Ogni mattina si spediva a Parigi il telegramma delle osservazioni fatte alle 7 antimeridiane colle
altre informazioni richieste, e si continua anche oggidì a spedirlo non sola a Parigi, ma a Firenze e
Pietroburgo, oltre alla diffusione dei listini meteorologici nei giornali, come si disse.
13 Le osservazioni raccolte dal Leverrier venivano poscia litografate e rinviate così raccolte agli
osservatorii. Fu su questi bullettini che all’osservatorio si studiarono da principio le leggi delle
burrasche.
14 The branch of meteorology that analyses meteorological observations carried out simultaneously
over a large area of the globe in order to forecast the short, medium, and long-term evolution of
weather.
9 Angelo Secchi and Meteorology in Italy