_ Sxor. IT] FORM AND SIZE OF THE EARTH. ia 
and which is surrounded with an atmosphere of glowing vapour. 
According to Mr. Lockyer, those stars which have the highest tem- 
perature have the simplest spectra, and in proportion as they cool 
their materials become more and more differentiated into what we 
eall elements. He remarks that the most brilliant or hottest stars 
show in their spectra only the lines of gases, as hydrogen. Cooler 
stars, like our sun, give indications of the presence, in addition, 
of the metals—magnesium, sodium, calcium, iron. A still lower 
temperature he regards as marked by the appearance of the other 
metals, metalloids, and compounds.” The sun would thus be a star 
considerably advanced in the process of differentiation or association 
of its atoms. It contains, so far as we know, no metalloid except 
carbon, and possibly oxygen, nor any compound, while stars like 
_ Sirius show the presence only of hydrogen, with but a feeble pro- 
portion of metallic vapours; and on the other hand, the red stars 
indicate by their spectra that their metallic vapours have entered 
into combination, whence it is inferred that their temperature is 
lower than that of our sun. 
Il. ForM AND SIZE OF THE EHARTH. 
Further confirmation of the foregoing views as to the order of 
planetary evolution is furnished by the form of the earth and the 
arrangement of its component materials. 
That the earth is an oblate spheroid, and not a perfectly spherical 
globe, was discovered and demonstrated by Newton. He even 
calculated the amount of ellipticity long before any measurement 
had confirmed such a conclusion. During the present century 
numerous arcs of the meridian have been measured, chiefly in the 
northern hemisphere. From a series made by different observers 
between the latitudes of Sweden and the Cape of Good Hope, Bessel 
obtained the following data for the dimensions of the earth :— 
Equatorial diameter . . 41,847,192 feet, or 7925°604 miles. 
Polar diameters. 4 . 41,707,314 ~ ,, - 7899-114, 
Amount of polar flattening 395768 © sy 2OP STS 5, 
The equatorial circumference is thus a little less than 25,000 
miles, and the difference between the polar and equatorial diameters 
(nearly 263 miles) amounts to about ;1,th of the equatorial 
diameter.* More recently, however, it has been shown that the oblate 
spheroid indicated by these measurements is not a symmetrical body, 
the equatorial circumference being an ellipse instead of a circle. 
The greater axis of the equator lies in long. 8° 15’ W.—a meridian 
passing through Ireland, Portugal and the north-west corner of Africa, 
and cutting off thenorth-east corner of Asia inthe opposite hemisphere.# 
* Huggins, Proc. Roy. Soc. 1863-66, and Brit. Assoc. Lecture (Nottingham, 1866) ; 
Huggins and Miller, Phil. Trans. 1864. 
Lockyer, Comptes-rendus, Dee. 1873. __ 3 Herschel, Astronomy, p. 139. 
* A, R. Clarke, Phil. Mag. August 1878 ;' Encyclopedia Britannica, 9th edit. x, 172. 

