“Maidens that nightly toil the tangled fleece
Divine the coming tempest; in the lamp
Crackles the oil, the gathering wick grows dim.”
Virgil did not live in our cold climate, and knew nothing of the crackling in the fire, or in the ashes or coals which remain after the wood is consumed. The lamp exhibits it on a smaller scale, and perhaps he had noticed it when in company with the maidens. But it is sometimes noticeable even in the lamp or candle with us. A small particle of moisture will produce it, in a marked degree, at any time.
In winter, when the air is highly positive and cold, the candle can be blown out, and by another puff of the breath relighted, with ease. But when the electricity before a storm becomes negative, and partial condensation takes place, this can not be done. This partial condensation before storms and showers shows itself upon vessels containing cold-water, in summer. It seems to be the received opinion, that the condensation is evidence of a greater quantity of moisture in the atmosphere. But this, too, is a mistake, and hence the little reliance to be placed on hygrometers.
This partial condensation is sometimes visible. When the sun shines clearly, at the east or west, through a small opening in the clouds, the condensing vapor is shown by the streaks of sunlight, just as the fine particles of dust are seen in a dark room, when a few rays of sunlight are admitted through a small aperture. This phenomenon is often observed, and it is said of it—“It’s a going to rain; the sun is drawing water.”
Virgil alludes to this as seen in the east in the morning, thus:
“But when beneath the dawn red-fingered rays
Through the dense band of clouds diverging break,
*******
Ill does the leaf defend the mellowing grape;
Leaps on the noisy roof the plenteous hail,
Fearfully crackling.”
It is well ascertained that storm-clouds of great intensity have polarity in the different portions, and that in the less intense magneto-electrical climate of England isolated showers are often of this character—the polarity existing in rings. Showers are doubtless thus found with us. Mr. Wise got into one of them; see his description (Theory and Practice of Aeronautics page 240).
I have, in another place, alluded to the upward attraction of the dust beneath the advance condensation of a shower. Jenner alludes to it in the following lines:
“The whirling winds the dust obeys,
And in the rapid eddy plays.”
So Virgil: