On the evening of the 3rd of the latter month, Mr. Cooper, of Markree Castle, observed a most singular cloud, which extended itself over the east of the range called the Ox Mountains, in the County Sligo, accurately imitating, in shape, a higher range of mountains somewhat more distant; afterwards an extremely white vapour, resembling a snow-storm, appeared along the southern declivity of the range. Mr. Cooper remarked to a friend at the time, that he thought this vapour might be charged with the fluid causing the disease in the potato. The friend to whom this observation was made, being a resident near those mountains, Mr. Cooper requested him to make enquiries on the subject. He afterwards informed him that on the same evening, or night, the blight fell upon the whole of that side of the mountain, where they had witnessed the strange appearance. It was noticed in various districts, that some days before the disease appeared on the potatoes, a dense cloud, resembling a thick fog, overspread the entire country, but differing from a common fog in being dry instead of moist, and in having, in almost every instance, a disagreeable odour. It is worthy of remark that from observations made by Mr. Cooper for a series of years, the average number of fogs for each year was a fraction under four,--the night fogs for each year not being quite two. In the year 1846, the night fogs were ten, the day two, being a striking increase of night fogs, in the year of greatest potato blight in Ireland.[114]