THE WEATHER DOG--It frequently happens in unsettled weather that banks of rain-cloud gather around the horizon, and that, over isolated tracts, the rain falls. If these depositions from this low stratum of clouds occur opposite to the sun, the lower limb of a bow is formed, often appearing like a pillar of decomposed light; and sometimes two of these coloured bands will be seen, forming indeed the two extremities of the arch. These are "weather dogs," and they are regarded as certain prognostications of showery or stormy weather. [a]
The usual proverb with regard to the full bow, which prevails generally, is common in Cornwall--
"The rainbow in the morning
Is the shepherd's warning;
The rainbow at night
Is the shepherd's delight."
But, as far as I know, the "weather dog" is peculiarly Cornish,
[a] "There appeared in the northeast the frustrum of a large rainbow; all the colour, were lively and distinct, and it was three times as wide as the arch of an ordinary complete rainbow, but no higher than it was wide. They call it here, in Cornwall, a weather dog; but in the Cornish language, Lagas-auel,--that is, the weather's eye,--and pronounced it a certain sign of hard rain."--Borlase's Natural History of Cornwall.