286 



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 re- 

 marked that a lufrge area of ordinary agri- 

 cultural land attached to a sewage-farm 

 does not always add to the profit of the un- 

 dertaking. 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 hab- 

 its of two green lizards, or American cha- 

 meleons, which she has kept in her rooms. 

 The first, a female, came from South Caro- 

 lina in November, and was kept in a room 

 warmed with a furnace. It was very lively 

 and ran about a great deal during the win- 

 ter, but paid no attention to the flies till the 

 warm spring-days came, when it greedily de- 

 voured them and eagerly lapped water with 

 its tongue. "When a male lizard was put in 

 the cage in May, a curious ceremonial court- 

 ship took place between the pair, each ani- 

 mal raising itself to the full extent of its 

 forelegs and bowing its head and the fore- 

 part 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 ob- 

 served ; and, if a fly came near them, they 

 would dart after it " like a flash of green 

 light." The changes of color in the creat- 

 ures were frequent and marked, but the 

 observations upon them were contradictory 

 and unsatisfactor)'. The changes were dif- 

 ferent 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 sunliirht, 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 chanjres 

 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 di- 

 rect 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 conven- 

 ient, 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 particu- 

 lar 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 frag- 

 ments. The lizard would seize a bit in his 

 mouth and pull it off as if it were an invert- 

 ed 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 re- 

 newed, as was the case with one of the liz- 

 ards, 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 re- 

 cently awarded a prize of twenty-five hun- 

 dred 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 here- 

 tofore 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 refrig- 

 erating processes that could be employed. 

 The principle of the new process consists in 



