The plant on which the Cochineal Insect is found, is called the _Nopal_, a species of Opuntia, or Prickly Pear, which abounds on all the coasts of the Mediterranean; and is thus described by Mr. Thompson, in his work entitled, _Official Visit to Guatemala;_ "The nopal is a plant consisting of little stems, but expanding itself into wide, thick leaves, more or less prickly according to its different kind: one or two of these leaves being set as one plant, at the distance of two or three feet square from each other, are inoculated with the cochineal, which, I scarcely need say, is an insect; it is the same as if you would take the blight off an apple or other common tree, and rub a small portion of it on another tree free from the contagion, when the consequence would be, that the tree so inoculated would become covered with the blight; a small quantity of the insects in question is sufficient for each plant, which in proportion as it increases its leaves, is sure to be covered with this costly parasite. When the plant is perfectly saturated, the cochineal is scraped off with great care. The plants are not very valuable for the first year, but they may be estimated as yielding after the second year, from a dollar and a half profit on each plant." The insect is famous for the fine scarlet dye which it communicates to wool and silk. The females yield the best colour, and are in number to the males as three hundred to one. Cochineal was at first supposed to be a grain, which name it retains by way of eminence among dyers, but naturalists soon discovered it to be an insect. Its present importance in dyeing is an excellent illustration of chemistry applied to the arts; for long after its introduction, it gave but a dull kind of _crimson_, till a chemist named Kuster, who settled at Bow, near London, about the middle of the sixteenth century, discovered the use of the solution of tin, and the means of preparing with it and cochineal, a durable and beautiful scarlet. Fine cochineal, which has been well dried and properly kept, ought to be of a grey colour inclining to purple. The grey is owing to a powder which covers it naturally, a part of which it still retains; the purple tinge proceeds from the colour extracted by the water in which it has been killed. Cochineal will keep a long time in a dry place. Hellot says, that he tried some one hundred and thirty years old, and found it produce the same effect as new. * * * * * LARGE CHESTNUT-TREE. There is now in the neigbourhood of Dovercourt, in Essex, upon the estate of Sir T. Gaisford, a chestnut-tree fifty-six feet in circumference, which flourishes well, and has had a very good crop of chestnuts for many years. J.T. * * * * * SPIRIT OF THE PUBLIC JOURNALS. * * * * * I'D BE AN ALDERMAN