J. L. LOBLEY — THE STUDr OF GEOLOGY. 175 



circumstances, or state of tilings, -which will bring new forces into 

 play, which will produce a new set of powers acting differently, 

 and perhaps producing similar results in less or in greater periods ? 



Permit me, now, to say a word or two on the use of what are 

 called scientific words or terms. These scientific words are, I 

 know, a terror to many, and prevent not a few from undertaking a 

 systematic study of science. But they ai-e by no means so for- 

 midable as they appear to the unaccustomed eye ; the eye and the 

 ear very soon become familiar with those that it is necessary to use 

 most frequently ; and when these are known, study is found to be 

 greatly facilitated. Scientific words are precise terms used to ex- 

 press clearly- defined ideas, and they accordingly frequently prevent 

 the necessity for the employment of a long phrase, a circumlocution, 

 or even an entire sentence. When, therefore, a scientific word is 

 used, the hearer knows at once exactly what is meant, and a precise 

 and definite idea is without any difiiculty immediately conveyed to 

 the mind, which would otherwise have been required to be con- 

 centrated upon the endeavour to obtain the full and correct meaning 

 of, perhaps, a long sentence. Another advantage which scientific 

 terminology has over ordinary expressions arises from the fact that 

 scientific words are usually made up of parts, each of which has a 

 definite meaning, and that they are therefore very expressive and 

 descriptive, and so greatly assist the memory. When it is borne in 

 mind, also, that, being classical, they can be used in all languages, 

 their great value and superiority over ordinary words and terms 

 will be at once acknowledged. 



Since our science relates to the earth and the materials of which 

 it is composed, it is, in the first place, necessary that we should 

 endeavour to obtain a clear and definite idea of the shape and size 

 of the earth. We have all been taught at school that the earth is 

 round, that it is a globe ; and we have, moreover, been told that it 

 is round like an orange. Now this latter statement is to be dis- 

 tinctly remembered. The earth is globular, it is true ; but it is 

 round, not like a ball or perfect sphere, but simply round like an 

 orange ; or, in other words, it is a globe slightly flattened at 

 each side. To be more exact, the earth is an oblate spheroid or 

 ellipsoid. 



If we take a sphere made of wire, or any material not rigid, and 

 cause it to rotate rapidly around an axis on which it is free to 

 collapse, we shall see that the axial diameter, or the diameter 

 around which the sphere is rotating or revolving, decreases in 

 length, and that the diameter at right angles to the axis, the 

 transverse or equatorial diameter, increases correspondingly. The 

 sphere will consequently be slightly flattened at each side, and will 

 thus assume the shape of the earth, the flattened sides of which 

 are also at the ends of the axis around which it rotates, or at 

 the north and south poles. The -bulging out or increase of the 

 equatorial diameter of the sphere, and the consequent flattening 

 at the poles, are due to centrifugal force which gives to mutter 

 rapidly revolving a tendency to fly outwards. This supports the 



