changes in atmospheric pressure at the first light
of day. Similar observations were made in Jena and
Potsdam, in Germany, but also in Washington,
where they appeared less intense than the Euro-
pean ones. The few Asian recordings were far more
marked. Particularly interesting were the Potsdam
measurements, which revealed both direct waves,
recorded on the morning of June 30 , and return
waves, recorded on the morning of July 1 st. Similar
measurements were made by observation stations
in Cambridge and Petersfield, England, thanks to
which it was possible to establish that the pressure
wave had passed at a speed of just over 300 meters
per second, absolutely comparable to that pro-
duced in 1883 by the Krakatoa volcano explosion.
Further east in Kansk, Siberia (about 500 km north
of Mongolia), an observing station recorded violent
seismographic and barographic oscillations and in-
formed the Central Seismic Commission of St. Pe-
tersburg. The Commission, however, considered the
report to be senseless since Siberia was not consid-
ered a seismic zone. Recordings of that same type
performed by the Irkutsk Magnetic and Meteoro-
logical Observatory, another observational stationTunguska 111 EN_l'Astrofilo 29/08/2019 15:43 Page 27