52 National Geographic Magazme. 
and appears to undergo a series of successive transformations, 
more or less affected by the topographical nature of the country 
passed over. . 
Ferari thinks their principal cause is to be found in high tem- 
peratures coincident with high vapor pressures. ‘Thunder storms, 
he considers, are essentially local phenomena, superposed on the 
general atmospheric phenomena. A principal general cause of 
thunder-storms in Italy is the existence of a deep depression in — 
northwest Europe, with a secondary depression in Italy depend- 
ent on the first. This secondary feeble area remains for several 
days over upper Italy, and nearly always is followed by thunder 
storms. Minimum relative humidity precedes, and maximum 
follows a storm, while the vapor pressure conditions are exactly 
reversed. Ferari notes, as one matter of interest, the passage of 
fully developed thunder storms from France into Italy over 
mountains 4,000 metres (18,000 feet) in elevation. 
Dr. Meyer, at Gottingen, has investigated the annual periodic- 
ity of thunder storms, while Carl Prohaska has made a statistical 
study of similar storms in the German and Austrian Alps. The 
latter writer thinks they are most likely to occur when the 
barometer is beginning to rise Se a fall, thus resembling heavy 
down-pours of rain. 
In connection with Schmucher’s theory on the origin of thun- 
der storm electricity, Dr. Less has been able to satisfactorily 
answer in the affirmative an important point in the theory, as to 
whether the vertical decrement of temperature is especially 
rapid. Less finds evidences of very rapid decrement of tempera- 
ture during thunder storms, as shown by the examination of 
records of 120 stations for ten years. 
Mohn and Hildebrandsson have also published a work on the 
thunder storms of the Scandinavian peninsula. The rise in the 
barometer at the beginning of rain, they agree with Masecart in 
attributing largely to the formation of vapor and the evaporation 
of moisture from rain falling through relatively dry air. 
A. Croffins has discussed thunder storms at Hamberg from 
observations for ten years. He believes that all such storms are 
due to the mechanical interaction of at least two barometric 
depressions. ‘ 
As a matter of interest bearing on the much discussed phe- 
nomena of globular lightning, an incident is recounted by F. 
Roth, where a man feeding a horse was struck by lightning and 
