PRACTICAL EXERCISES IX GEOGRAPHY 77 



grams that one usually finds in text-books, although they are much 

 less serviceable than globes* Whether children of under fourteen 

 years of age can discover this solution of the problem or not remains 

 to be proved. At least they should have a good chance to show their 

 capacity to discover it, a carefully prepared chance, approached by 

 the slow accumulation of pertinent observations, all familiarized by 

 repetition. 



A simple construction of the earth's orbit is also serviceable at this 

 stage. Draw upon a sheet of pajjer about a foot square a line througli 

 its middle j^arallel to one side. Locate the middle point of the line. 

 Construct a scale whose units are ^^-^ of the side of the paper, so that 

 two pins, three units apart, can be driven into the middle line sym- 

 metrically on either side of the middle point. Lay a loop of thread 

 or fine string 189 units in perimeter over the pins ; stretch it tight 

 with a ])encil, and draw a curve thus guided. This curve shows the 

 true pattern of the earth's orbit, the units of the scale being millions 

 of miles. The orbit is as sensibl}^ circular as are the earth's meridians. 

 Take out one of the pins, and around the other draw a little circle, 

 a trifle less than a unit in diameter, to represent the sun ; a good- 

 sized pin-head will not be much too small for it. Assuming that the 

 North star is above the plane of the orbit (or paper), the earth moves 

 around the orbit so as to pass from right to left when viewed from 

 the sun. Find the point on the orbit that is nearest to the sun 

 (it must lie where the orbit is cut by that half of the middle line 

 which passes through the sun). Conveniently for our memories, 

 the sun celebrates New-Year's day by passing through this near-sun 

 point, or perihelion. July 1 sees the earth at the opi)Osite far sun 

 point, or ai)helion. Go backward along the orljit from perihelion 

 one-ninth of a quadrant arc ; this is the point occupied on Decem- 

 ber 21, the date of the sun's least midday altitude, or the winter 

 solstice. Draw a line from this point through the sun; it intersects 

 the orbit at the summer solstice, which the earth passes on June 21. 

 Draw a line through the sun at right angles to the solsticial line; it 

 intersects the orbit in the equinoctial points. Set up a small ball on 

 a vertical axis to represent the earth at the winter solstice; the sun 

 can then be imagined to illuminate the near half of the eartli ; the 

 day-and-night circle will se[)arate the illuminated half from the dark 

 half of tlie earth. As the earth now stands, with a vertical axis, tlie 



* A Sim pi o, small uml i-heaii " cIcnii'iilMfy «lolic," divi'stcd i<\' nearly all iiannv-. and sIm.u inn 

 only tin; most geniTul ri.'llef, i.-i pn'ilisliril l,y A. Donnelly, ( ».\ li.r.l, N. \. 



