OF THE HEAVENS AND THE EARTH. 287 



globe better, but would also make the problems thereon LECT. 

 much easier. vm.&ix. 



In order to form a true idea of the earth's motion 

 round its axis every 24 hours, which is the cause of day 

 and night ; and of its motion in the ecliptic round the 

 sun every year, which is the cause of the different 

 lengths of days ( and nights, and of the vicissitude of 

 seasons ; take the following method, which will be both 

 easy and pleasant. 



Let a small terrestrial globe, of about three inches An idea of 

 diameter, be suspended by a long thread of twisted 

 silk, fixed to its north pole : then having placed a lighted 

 candle on a table, to represent the sun, in thejcenter of a 

 hoop of a large cask, which may represent the eclip- 

 tic, the hoop making an angle of 23j degrees with the 

 plane of the table; hang the globe within the hoop near 

 to it ; and if the table be level, the equator of the globe 

 will be parallel to the table, and the plane of the hoop 

 will cut the equator at an angle of 23j degrees ; so that 

 one half of the equator will be above the hoop, and the 

 other half below it : and the candle will enlighten one 

 half of the globe, as the sun enlightens one half of the 

 earth, whilst the other half is in the dark. 



Things being thus prepared, twist the thread towards 

 the left hand, that it may turn the globe the same way 

 by untwisting ; that is, from west, by south, to east, 

 As the globe turns round its axis or thread, the differ- 

 ent places of its surface will go regularly through the 

 light and dark ; and have, as it were, an alternate re- 

 turn of day and night in each rotation. As the globe 

 continues to turn round, and to shew itself all around 

 to the candle, carry it slowly round the hoop by the 

 thread, from west, by south, to east ; which is the way 

 that the earth moves round the sun, once a year, in the 

 ecliptic : and you will see, that whilst the globe conti- 

 nues in the lower part of the hoop, the candle (being 

 then north of the equator) will constantly shine round 



