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THERMOMETER

Much annoyance is caused by the great difference of thermometer scales in use in the different civilized countries. The scale of Reaumur prevails in Germany. As is well known, he divides the space between the freezing and boiling points into 80 deg. France uses that of Celsius, who graduated his scale on the decimal system. The most peculiar scale of all, however. is that of Fahrenheit, a renowned German physicist, who in 1714 or 1715, composed his scale, having ascertained that water can be cooled under the freezing point, without congealing. He therefore did not take the congealing point of water, but composed a mix

SCALES.

ture of equal parts of snow_and_sal ammoniac, about 14 deg. R. The conversion of any one of these scales to another is very simple, and easily made. To change a temperature as given by Fahrenheit's scale into the same as given by the centigrade scale subtract 32 deg. from Fahrenheit's degrees, and multiply the remainder by 5-9. The product will be the temperature in centigrade degrees.

To change from Fahrenheit's to Reaumur's scale, subtract 32 deg. from Fahrenheit's degrees, and multiply the remainder by 4-9. The product will be the temperature in Reaumur's degrees.

COMPARATIVE SCALES OF THERMOMETER.

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To change the temperature as given by the centigrade scale into the same as given by Fahrenheit, multiply the centigrade degrees by 9-5 and add 32 deg. to the product. The sum will be the temperature by Fahrenheit's scale.

To change from Reaumur's to Fahr

enheit's scale, multiply the degrees on Reaumur's scale by 9-4 and add 32 deg. to the product. The sum will be the temperature by Fahrenheit's scale.

For those who wish to save themselves the trouble we have calculated the preceding comparative table.

CHAPTER II.

ASTRONOMY AND TIME.

EDITED BY A. RUSSELL BOND.

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The temperature increases on an average about 1° F. for every,64 feet descent. But this amount is variable according to the locality, geological formation, and dip of strata. In the Calumet and Hecla Mines, observations show an increase of 1° in about every 125 feet. At Bendigo it is shown to be 1° per 80 feet of descent. At Ronchamp Collieries, on the other hand, the temperature increases 1° F. in only 49 feet.

The mean density of the earth is 5.53 times as great as that of an equal bulk of water. Area in sq. miles:

Africa.

North America.

11,514,000

6,446,000 6,837,000 14,710,000 3,288,000

3,555,000 4,888,800

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-Science Year Book.

The Earth is not always at the sume distance from the Sun. In the Nautical Almanac the sun's apparent semi-diameter is given for every day in the year. The apparent semi-diameter was 16′ 17′′. 89 on January 1st, 1912, and on July 1st of the same year it was 15' 45". 68. This proves that a greater distance separates us from the sun in summer than in winter.

PERIHELION AND APHELION.-When the earth is nearest to the sun it is said to be in Perihelion, and when farthest from the sun it is said to be in Aphelion.

THE EARTH MOVES WITH VARYING VELOCITY IN ITS ORBIT.-This is ascertained by measuring the sun's longitude for two successive days at different times of the year. by which means it is found in December to move over 61'10.0" within a period of twenty-four hours, while in June it only moves over 57'10.8" in the same time.

KEPLER'S LAW OF EQUAL AREAS.-Kepler found that the line joining the center of the sun with the center of the earth moved over equal areas in equal times, that is, the greater distance of the earth from the sun in June compensated for the smaller arc of motion in longitude, so that lines drawn from the sun to the extremities of the arcs moved over make equal triangles.

REVOLUTION OF THE EARTH IN ITS ORBIT. -The stars which are seen nearest to the sun after sunset at different times of the year are not the same, but belong to different signs of the zodiac. This change of position of the sun with respect to the stars takes place at the rate of about 1° a day, so that the whole heavens appear to revolve once in a year independent of their diurnal revolution. This is due to the real revolution of the earth in its orbit. The stars appear to describe little ellipses in the course of a year, but, as a matter of fact, it is the light coming from the stars that is displaced by the motion of the earth in its orbit. This phenomenon is known as the aberration of light. There is also an apparent displacement of the nearer stars with respect to those more distant, which is known as annular parallax and is used to measure the distance of stars; for the greater the displacement the nearer must be the star.

THE MOON.

The moon, our only satellite, is on the average 238,850 miles away, measuring from centre of the earth to the centre of the moon. Its maximum distance is 252,830 and minimum 221,520. After subtracting the semidiameter of the earth, and the semi-diameter of the moon from this figure, we find that the minimum possible distance between the surfaces of the planets is 216,476 miles. The moon is only 2,162 miles in diameter, and its surface area is 14,685,000 miles, or a little less than the combined areas of North and South America. The volume of the earth is 49 times that of the moon and its weight, or more strictly speaking, its mass, is 81 times greater. A man weighing 140 pounds on earth would weigh but 21 pounds on the moon. The surface of the moon is covered with tall mountains reaching 20,000 feet high, with deep craters and crevasses. The moon has no atmosphere and apparently is a dead world. It revolves about the earth once in 27d., 7h., 43m., 11.55s. or 27.32166 days. However, as the earth is also revolving about the sun the synodical period or the time from new moon to new moon is 29d., 12h., 44m., 2.86s. or 29.53059 days. During the synodical period the moon makes one complete rotation about its axis, and hence the moon's day is almost a month long. During this period it keeps the same face always toward the earth. However, we can see more than half of the moon because the moon's axis is inclined 5° 8'from the perpendicular to its orbit, so that we can see alternately its north and south pole. Also because its angular velocity about its orbit varies, we can see a little more now of the western side and now of the eastern. The moon does not revolve about the centre of the earth, but about a centre of gravity common to both earth and moon. This centre is 1,063 miles below the surface of the earth. The earth's revolutions about this centre are known as librations. The plane of the moon's orbit is also inclined to the earth's orbit 5° 5. The points where this plane crosses the plane of the earth's orbit are called the nodes. Eclipses occur only when the moon is at or near the nodes. For only then can its shadow fall on the earth or the earth's shadow fall on the moon. The nodes are not fixed, but move at the rate of one complete revolution in 18y., 218d., 21h., 22m., 46s. This period was known to the ancients as a saros for it was noted that eclipses repeated themselves at the lapse of such a period.

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Showing approximately

TE

SECTION OF THE EARTH.

At about this height is the "isothermal layer,' above which But this increase of temperature is, of course, solely a matter of conjecture, and many theoriess deny the possibility of the curvature, the relative heights of the loftiest mountains and highest clouds, the greatest depth of the ocean, and The thickness of the black line suggests the limits practically inhabited by man, i.e., from the bottom of the deepest mine to the highest At an elevation of about seven miles (36,000 feet) the atmospheric pressure is one-third that at sea level, so that two-thirds of the atmosphere Presuming the temperature to increase at a rate of 1° F. for each 60 feet of descent into the earth (a general average as found at depths up to 1 mile), then at 10 miles all would be at red-heat, and at 30 miles a temperature would be reached at which all known substances would this thin crust of solid earth enclosing so vast a bulk of molten and liquid matter. The pressure of the superincumbent crust may also raise is below this line, the remainder extending upwards in increasing attenuated form. the melting point of mineral matter down below. habitation in Europe, about 10,000 feet. the temperature of the air changes but little. the thickness of the solid crust. be in a molten state.

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M

O

THE SUN,

-Solar Parallax (equatorial horizontal), 8.80"+0.02". Mean distance of the sun from the earth, 92,885,000 miles; 149,480,000 kilometers. Variation of the distance of the sun from the earth between January and July, 3,100,000 miles: 4,950,000 kilometers. Linear value of 1" on the sun's surface, 450.3 miles; 724.7 kilometers. Mean angular semidiameter of the sun, 16′ 02.0". Sun's linear diameter, 866,400 miles; 1,394,300 kilometers. (This may, perhaps, be variable to the extent of several hundred miles.) Ratio of the sun's diameter to the earth's 109.3. Surface of the sun compared with the earth, 11,940. Volume, or cubic contents, of the sun compared with the earth, 1,305,000. Mass, or quantity of matter, of the sun compared with the earth, 330,000+3000. Mean density of the sun compared with the earth, 0.253. Mean density of the sun compared with water, 1.406. Force of gravity on the sun's surface compared with that on the earth, 27.6. Distance a body would fall in one second, 444.4 feet; 135.5 meters. Inclination of the sun's axis to the ecliptic, 70° 15'. Longitude of its ascending node 74°. Date when the sun is at the node, June 4, 5. Mean time of the sun's rotation (Carrington), 25.38 days. Time of rotation of the sun's equator, 25 days. Time of rotation at latitude 20°, 25.75 days. Time of rotation at latitude 30°. 26.5 days. Time of rotation at latitude 45°, 27.5 days. (These last four numbers are somewhat doubtful, the formulæ of various authorities giving results differing by several hours in some cases.) Linear velocity of the sun's rotation at its equator, 1:261 miles per second; 2.028 kilometers per second. Total quantity of sunlight, 1,575,000,000,000,000,000,000,000,000 candles. Intensity of the sunlight at the surface of the sun, 190,000 times that of a candle flame; 5300 times that of metal in a Bessemer convertor; 146 times that of a calcium light; 3.4 times that of an electric arc. Brightness of a point on the sun's limb compared with that of a point near the center of the disk, 25 per cent. received per minute from the sun upon a square meter, perpendicularly exposed to the solar radiation, at the upper surface of the earth's atmosphere (the solar constant), 20 calories. Heat radiation at the surface of the sun, per square meter per minute, 1,117,000 calories. Thickness of a shell of ice which would be melted from the surface of the sun per minute, 481⁄2 feet, or 14 34 meters. Mechanical equivalent of the solar radiation at the sun's surface, continuously acting, 109,000 horse power per square meter; or, 10,000 (nearly) per square foot. Effective temperature of the solar surface about 5,000° C., or 9,000° F.

Heat

ECLIPTIC.-If the brilliance of the sun did not obscure the stars, in other words, if we were able to see the stars by day as we do at night, we should note that the sun travels eastward among them, making a complete revolution in a year. The path of the sun among the stars is known as the "Ecliptic." The angle (2310) between the plane of the ecliptic and that of the celestial equator is known as the obliquity of the ecliptic. The sun's motion is only apparent. The plane of the ecliptic is really the plane of the earth's revolution about the sun, while the plane of

the celestial equator is the plane of the earth's rotation on its axis.

NODES.-The two points where the plane of the ecliptic crosses the plane of the celestial equator or equinoctial are called nodes, that point at which the sun appears to come up from below the equator being called the ascending node, and that at which the sun appears to descend from above the same plane being called the descending node.

THE FIRST POINT OF ARIES.-The ascending node above referred to is the first point of Aries. It is universally used for fixing the right ascension of celestial bodies.

PRECESSION AND NUTATION.-The sun and moon attract the protuberant portion of the earth's equator more on that side nearest to them than on that side farthest away, and in this way the differential attraction tends to tilt the axis a little, so that it describes a circle in about 25,800 years. The moon's differential attraction is greater than that of the sun. On account of the moon's continually changing its relation to the earth's equator, it causes the axis of the earth to describe a circle with a wavy circumference, known as nutation, or nodding of the earth's axis.

AND

LATITUDE, LONGITUDE, RIGHT ASCENSION, DECLINATION.-Terrestrial latitude is measured from the equator to the poles, north and south. Terrestrial longitude is commonly measured from the meridian of Greenwich, but some countries use their own meridians. Right ascension is measured from the first point of Aries. Declination is measured from the celestial equator. Celestial longitude is measured from the first point of Aries, celestial latitude from the ecliptic.

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1. Mimas..... 2. Enceladus. 3. Tethys.... 4. Dione. 5. Rhea.

6. Titan.

22 37 6: W. Herschel. 1853 7 W. Herschel.

1 21 18 26 J. D. Cassini.

July 18, 1780

Aug 29, 1789

934.000 21 6 39 27 G. P. Bond. 2,225.000 70 7 54 17 J. D. Cassini. 8.000.000 546 5 d. WH Pickering 906,000 20 20 24 of W.H.Pickering

Oct. 25. 1671

1895 1905

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