Science Sittings

New Zealand Tablet, Volume XXXVII, Issue 20, 20 May 1909, Page 35

Science Sittings

BY * VOLT

The Heat of the Sun.

There is one thing in connection with the heat of the sun that many people do not understand (says the Chicago News). Citing the well-known fact that the nearer we get to a fire the more we feel its heat, they ask why it is that we find the air so much colder on the top of a high mountain than on the plain below. On the plain the sun's rays pour down with an intensity that causes actual suffering, while on the mountain three miles nearer the source of heat there is perpetual snow. That apparent inconsistency is perfectly understood 'by those that have given even casual study to atmospheric phenomena, for it is in the earth's atmosphere that the cause may be found. The sun's rays impart little of their heat to the air. It is the surface of the earth that they warm, and their radiation from the surface warms the superincumbent air. It is a law of nature that all hot bodies throw off their heat into space. The earth throws off at night part of the heat that it receives from the sun during the day. It would throw it off with almost equal facility during the day if it were not for the atmospheric coat that surrounds it. That atmospheric coat may be compared to the glass roof of a hothouse — it permits the sun's heat to enter readily, but prevents it from escaping. We see, therefore, why in precisely the same latitude the heat on the plains may be so great as to parch the vegetation, while on the mountain top there may be snow and ice the •whole year around. The air is so dense on the lower levels that free radiation of heat from the earth's surface is impossible. Therefore the lower levels are warm. But on the mountain top the air is not nearly so dense, and heat is thrown off into space almost as fast as it is received.

Isinglass and Gelatine.

The difference between isinglass and gelatine is mainly one of source and quality, isinglass being a very pure variety of fish gelatine. Originally isinglass was obtained from the sturgeon only, and consisted of the dried air bladder of that fish. This is still the source of the finestqualities, which come from Russia, but it is also obtained from the sounds of other fishes. Isinglass is largely 'used for clarifying liquors, its chief value in this respect being due to its fibrous structure, the crossing threads formng a fine network in the liquid, which mechanically carries down all the minute particles that render the liquor cloudy and turbid. Gelatine, which generally occurs in thin, elastic, brittle plates, is obtained from bones, skin, tendons, horns, hoofs, etc., by boiling in water. On cooling, the solution gelatinises, or forms a jelly, which, when dried, becomes gelatine, size, or glue, according to the source from which it is derived. The best gelatine for dietic purposes is obtained from calves' heads and feet, but it is not desirable to inquire too closely into the source of what we find at table.

World's Largest Bridge.

The Pennsylvania Railroad has filed plans for building the largest bridge in the world. It will connect the mainland of New York with Long Island, and, with its approaches, will be three miles long. The greatest span over Hell Gate Channel will be 1000 feet long. The bridge will be 140 feet over the water, permitting the passage of the biggest vessels. The entire structure, except the piers for the arch, will be of steel, having an estimated weight of 80,000 tons. It- will have four tracks — two for passenger trains and two for freights — and is designed for live loads on each of the tracks of two 190-ton locomotives, followed by a uniform load of 50001 b per lineal foot. The estimated cost is between £3,000,000 and £4,000,000. -

-^Thunderstorms and Milk.

It is well known that milk often turns gour during a thunderstorm, and various reasons have been assigned (says the Chicago News). One of the reasons is that lightning causes the gases of the air to combine and produce nitrio acid, and that some of this acid mixes with the milk, thus souring it. But the most probable reason is that the souring is due to -the growth of a fungus in the milk which forms at other times than during a, storm, but more freely then because the atmospheric conditions favor it. Scientists have investigated this matter, and they say that milk will seldom turn sour if the cows are given the right kind of food and the milk vessels are kept perfectly clean.

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