Aurora and Thunder-storms.
Aurora and thunder-storms. Silbermann’s theory.
Silbermann asserts that Auroræ are produced by the same general phenomena as thunder-storms, and concludes that the Auroræ of 1859 and 1869 assumed the character of thunder-storms which, instead of bursting in thunder, had been drawn into the upper parts of the atmosphere, and their vapour being crystallized in tiny prisms by the intense cold, the electricity became luminous in flowing over these icy particles.
Prof. Piazzi Smyth on monthly frequency of Auroræ and storms.
Professor Piazzi Smyth has observed that the monthly frequency of Auroræ varies inversely with that of thunder-storms. His Table of comparisons is as follows:—
His table of observations.
| Month. | Lightning. | Auroræ. |
|---|---|---|
| January | 24·0 | 29·7 |
| February | 14·4 | 42·5 |
| March | 7·0 | 35·0 |
| April | 15·4 | 27·5 |
| May | 37·4 | 4·8 |
| June | 48·0 | 0·0 |
| July | 55·2 | 0·5 |
| August | 38·4 | 12·6 |
| September | 22·4 | 36·6 |
| October | 20·8 | 49·4 |
| November | 15·0 | 32·4 |
| December | 15·0 | 28·8 |
| Mean of whole year | 24·0 | 20·1 |
Silbermann’s observations 15th April, 1869. 30th April, 1865.
Silbermann, on 15th April, 1869, observed a fall of rain (tiny crystals of ice) on the disappearance of an Aurora and its change into cloud forms (see section, “Auroræ and Clouds,” p. 53). He also observed a rain of little sparkling ice-prisms on 30th April, 1865, at Paris, the city being then enveloped in a cirrus of vertical fibres similar to that which frequently accompanies the Aurora.