Page:Popular Science Monthly Volume 29.djvu/148
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��THE POPULAR SCIENCE MONTHLY.
��sites of a good sprinkler are that the solder should fuse at a low and well-defined tem- perature, without any appreciable prior soft- ening; that the mechanism should not be liable to get out of order or stick ; that the parts opened by heat should be capable of ready replacement without skilled labor; that there should be no leakage at the valve ; and that the quantity of solder to be melted should be small, and so placed that it is not cooled by contact with too great a mass of metal, or exposed to the drip of the opening valve. Closely allied to the auto- matic sprinkler proper is the system of sprinkling by perforated pipes through an automatic valve. The automatic fire-door, which should not be of iron, because it curls up, but of wood protected by sheathings of tin-plate, is arranged to shut on an inclined track, and is kept open by a rod made with a scarf -joint in two parts twisted in the center, and secured by a fusible solder ; or the door may be held by a cord holding a weight, the fall of which releases the door ; the fall to be produced by the melting of a solder set in some convenient part of the cord. Another class of devices depends upon the introduction into the electric cir- cuit of a fusible link, the melting of which breaks the circuit ; or into the broken cir- cuit of a strained catgut band, the contrac- tion of which by the heat brings the wires into contact. In one of the applications of this system a reservoir of carbonic acid is opened and the acid distributed. Mr. John has invented an arrangement for making the hand grenade extinguisher automatic. He proposes to hang the grenade at the top of a room in a sort of a cage, which is pro- vided with a small button held together with fusible alloy. When that is affected by the ascending hot air, the button bursts, and the cage opens and allows the grenade to fall, while an iron weight follows it, and, break- ing it in mid-air, causes the liquid to be sprinkled about.
Parasitic Fungi on Plants. Professor T. J. Burrill, in a paper of the Illinois State Laboratory of Natural History on the para- sitic fungi of the State, remarks with ref- erence to the nature of these pests, that " during the last part of the first half of this century learned discussions arose upon
��the specific distinction between the parasite and the host, and esteemed botanists held the view that what was taken for the for- mer was but a diseased condition of the lat- ter the rust of wheat, for example, was only the degraded cell-tissues of the wheat itself. Such difference of opinion, however, no longer exists among those who have pos- session of the information now acquired. The tissues of higher plants do not change by any process of degradation or transfor- mation into the things called fungi, neither do the latter originate in any other manner than as descendants of pre-existing forms through as rigid specific lines as can be traced among any animals or plants. It is known, too, that however much the fungus is found within the tissues of the host-plant, it began its growth outside of the latter, and gained introduction only by forcible en- trance. Spores are never taken up by ab- sorption and carried by the aqueous cur- rents from part to part of the plant. The fungus passes through the tissues very much as roots pass through soil, sometimes appar- ently without in any degree successful op- position, sometimes nearly or quite baffled in the struggle by the mechanical and physio- logical resistances of the host-plant."
The Punjab. The Punjab derives its name which means " five waters " from the five great rivers traversing it the Jhe- lum, Chenab, Ravi, Beas, and Sutlej which, united, flow into the Indus about five hun- dred miles above its mouth. In early times the country was called the land of the " seven rivers," and the Indus itself, on the one side, and the Saraswati, on the other side, were counted in addition to the five streams already named. The Saraswati, according to General R. Maclagan, presents an interesting problem. All the other rivers of the seven take their rise in the snows of lofty mountains, and, being fed from unfail- ing sources, are always great streams ; but the Saraswati rises in the low outer hills, depends on periodical rains only, and, while subject to floods, is dry for a great part of the vear. Even in the flood season, the water with which its upper valley is inun- dated runs off so quickly that it all disap- pears before it can reach the Sutlej or the Indus. Yet in the ancient Indian writings