EARTH-SHINE 



EARTHWORM 



Earth-shine. Illumination of 

 the moon by reflected light from 

 the earth. It can be observed 

 with greater or less distinctness, 

 according to locality and atmo- 

 spheric conditions, when the por- 

 tion of the moon illuminated by 

 the sun appears only as a slender 

 crescent. The earth-shine on the 

 new moon was successfully photo- 

 graphed in Feb., 1895, at the Lick 

 Observatory by Prof. Barnard, 

 who thus described it : *' The earth- 

 lit globe stands out beautifully 

 round, encircled by the slender 

 crescent. All the seas are conspicu- 

 ously visible, as are also the other 

 prominent features, especially the 

 region about Tycho. Aristarchus 

 and Copernicus appear as bright 

 specks." Huniboldt endorses an 

 observation that the light reflected 

 thus on the moon changes in colour 

 according to the region of the 

 earth which reflects it. See Moon. 



Earth-star (Geaster). Genus 

 of fungi, of the natural order 

 Gastromycetes. They are distin- 



Earth-star. Specimen of the fungus 

 showing its pointed segments 



guished from the puff-balls (Lyco- 

 perdon) by the two outermost 

 layers splitting from the apex into 

 several pointed segments which 

 expand and give the plant its 

 stellate form. The numerous 

 species grow upon the ground. 



Earthwork. Ancient strong- 

 hold defended by earthen mounds. 

 There are several thousands in 

 England and Wales. Promontory 

 forts, utilising natural defences, 

 are either coastal or inland. They 

 developed into cliff castles. Hill- 

 forts are characteristic of neolithic 

 Britain. Plateau forts are on 

 flatter ground. When round or 

 oval they are pre-Roman, but often 

 were used successively by neo- 

 lithic, Celtic, Roman, Saxon, and 

 Norman occupants. There is a 

 good earthen hill-fort on Midhill 

 Head, Midlothian, but Scottish 

 strongholds are mostly of stone. 

 See Caesar's Camp ; Dyke ; Rath. 



Earthwork. In engineering, the 

 excavation and disposal of ma- 

 terials which can be loosened with- 



out blasting. Railway engineers, 

 when running their surveys, en- 

 deavour to fix formation levels 

 which will balance excavation and 

 embankment, preventing useless 



Earthwork. Diagram illustrating angle 

 of repose 



dumping and too much borrowing 

 from outside areas. 



The cubic contents of a cutting 

 or embankment relatively to its 

 average depth is governed by the 

 angle of repose of the material 

 under the conditions to which it 

 will be exposed when the work is 

 completed. If dry sand is poured 

 on to a horizontal surface A B (see 

 diagram), it forms a conical pile, 

 the slopes of which make an angle 

 of about 35 with A B. As long as 

 the heap remains dry, the angle is 

 unchanged, and the heap is stable. 

 Therefore angle C A B (= angle 

 C B A) is the natural angle of re- 

 pose. Addition of water reduces the 

 friction between the particles, and 

 the heap spreads out until a 

 condition of equilibrium is re- 

 established, the angle of repose 

 being reduced to 22-26. 



The angles of repose of other 

 substances are approximately : 

 damp clay, 45 ; wet clay, 16 ; 

 earth deposited in layers and 

 rammed, 60-70 ; damp earth 

 piled in bulk, 45 ; dry earth, 30 ; 

 wet earth, 16-18 ; gravel, 45- 

 50. Assuming that proper provi- 

 sion is made for drainage, a slope 

 in which A D : C D : : If : 1 is 

 safe for average earthwork in both 

 cutting and embankment. To 

 allow for the effect of heavy rain, 

 it may be prudent to make the 

 slope more gentle than this, as 

 extra work done in the first in- 

 stance is less expensive. The 

 shoulders and toes of embank- 

 ments should be rounded off, and 

 the slopes covered with grass, 

 which protects the earth against 

 the loosening influence of rain. 

 Ditches and Drainage 



If there be any likelihood of water 

 flowing down into a cut from higher 

 ground, a ditch is dug near the 

 edge to intercept the water and 

 carry it to a point where it can 

 pass away without doing damage. 

 In clay it is often necessary to 

 cut Y-shaped ditches in the direc- 

 tion of the slope and fill them in 

 with lump chalk, clinkers, etc. The 

 arms of a Y catch the water, 

 which flows down the leg into 

 permanent drains along the foot. 



A cutting is usually excavated 

 in successive 'lifts or layers, each 

 opened out by deep trenches tra- 

 versing the whole length of the 

 cutting. The faces of the trenches 

 are attacked by men working about 

 5 ft. apart, and extended laterally 

 till they meet the slopes or one 

 another. For very large cuttings 

 a system of terracing is sometimes 

 adopted, and work proceeds on a 

 number of longitudinal benches 

 on both sides at different levels, 

 each provided with its own tem- 

 porary way. A cut is made near 

 the centre line, and widened out to 

 three or four times its original 

 width, after which a second cut 

 is sunk under the first. While this 

 is being extended, the limits of 

 the cut above also are receding. 

 The process is repeated till forma- 

 tion level is reached. The same 

 system of benches is useful on side- 

 long ground, i.e. where a notch has 

 to be cut along the face of a hill. 

 Economic Removal of Spoil 



Mechanical excavators are em- 

 ployed wherever the scale of work 

 justifies their use. With hand- 

 work, 14-60 cubic yds. per man 

 per day can be loosened by picks ; 

 and 10-30 cubic yds. shovelled, 

 according to the nature of the 

 ground. Removal of the spoil is 

 effected most economically by 

 barrows over distances up to 

 500 ft., by two-wheeled carts, 

 500 ft.-l,700 ft.; by four-wheeled 

 carts, 1,700 ft. -3,500 ft. ; and by 

 wagons on rails for longer hauls. 



Railway embankments are gener- 

 ally formed by tipping over the end, 

 and allowing the debris to find its 

 own angle. Settlement of the 

 material by consolidation must be 

 allowed for to the extent of T ^ 

 to y of the height of the pile. 

 If the earth be spread in layers, 

 subsequent shrinkage is small. To 

 open the road quickly it may prove 

 economical to run a temporary 

 trestle across a fill and dump earth 

 from it to both sides. The stringers 

 are removed as the earth reaches 

 them ; the uprights and cross- 

 bracings are left in position and 

 help to give solidity. 



If the maximum density be 

 required, as for the embankments 

 of reservoirs and behind retaining 

 walls, earth is spread in layers a 

 few inches thick, and well rammed. 

 See Embankment ; Engineering. 



Earthworm. Segmented worm 

 living in the soiL Their rounded 

 shape and the short bristles with 

 which the segments are provided 

 enable the worms to push their way 

 through the soil and to form bur- 

 rows. They eat their way also, and 

 derive their food largely from the 

 vegetable matter contained in the 

 soil swallowed. When this has 



