THE POPULAR SCIENCE MONTHLY.
amount of capital engaged upon the several farms, and in the gross returns per acre. The gross returns and the amount of wages paid per acre were greatest in cases where market-gardening was in vogue. It was remarked that a large area of ordinary agricultural land attached to a sewage-farm does not always add to the profit of the undertaking. Statistical tables showing the number of persons living or working on the farms, and the number of children on them, make it appear that the average annual mortality upon them does not exceed three per thousand, and that "sewage-farming is not detrimental to life or health." About one hundred sewage-farms are in operation in England.
Habits of the Green Lizard.—Sarah P. Monks has contributed to "The American Naturalist" an interesting study of the habits of two green lizards, or American chameleons, which she has kept in her rooms. The first, a female, came from South Carolina in November, and was kept in a room warmed with a furnace. It was very lively and ran about a great deal during the winter, but paid no attention to the flies till the warm spring-days came, when it greedily devoured them and eagerly lapped water with its tongue. When a male lizard was put in the cage in May, a curious ceremonial courtship took place between the pair, each animal raising itself to the full extent of its forelegs and bowing its head and the forepart of the body in a regular and dignified manner as if it had a hinged joint at the shoulder. Both lizards would scamper off when they found that their actions were observed; and, if a fly came near them, they would dart after it "like a flash of green light." The changes of color in the creatures were frequent and marked, but the observations upon them were contradictory and unsatisfactory. The changes were different in the two specimens: the same causes did not affect them both alike; and the changes came on without regard to the object on which they were placed, or to the amount of light and darkness. They would become green or light-brown when placed in sunlight, but would also assume the same colors in the darkest room. When disturbed they would sometimes become darker, but at other times would not change. The changes were rapid, taking place in from two to eight minutes; and at one time one of the lizards changed from green to light-brown, then back to green again, in five minutes. They would go to sleep as soon as it became dark, and in the gloom of a storm, and would wake again on the appearance of the sun, although they were not exposed to its direct rays. They assumed various positions in sleeping—sometimes, when it was cool, lying close up under a bit of loose bark, sometimes curled in a corner behind a small jar, sometimes stretched out on a limb or along the twigs. When in a crevice or hole, they took any shape that was convenient, but on sticks and twigs they arranged themselves so as to imitate the general form of the branches. The changes of the skin do not appear to depend upon any particular time or season, but upon the general health and growth of the animal. One of the lizards changed twice in seventeen days, the other only four times in fire months. The skin split along the back and the upper sides of the legs, and came off in large fragments. The lizard would seize a bit in his mouth and pull it off as if it were an inverted glove, and would then eat it. The bits of skin that remained around the jaws and eyes seemed to annoy the animal very much. When the tail had been broken off and renewed, as was the case with one of the lizards, the exuviation of that part took place independently of the rest of the body.
The Safe Manufacture of Dynamite.—The French Academy of Sciences has recently awarded a prize of twenty-five hundred francs to Messrs. Boutmy and Foucher for introducing new modes of producing nitro-glycerine in quantity, by means of which the manufacture of dynamite has been rendered much safer than it has heretofore been. The old method, in which fuming nitric acid, or a mixture of that substance and sulphuric acid, was made to act on glycerine, and the mass was suddenly immersed in water, often resulted in the production of enough heat to decompose a part of the nitro-glycerine, and occasion a violent explosion in spite of the best refrigerating processes that could be employed. The principle of the new process consists in