17. The plate under thy riet is descryved with 3 principal cercles; of which the leste is cleped the cercle of Cancer, by-cause that the heved of Cancer turneth evermor consentrik up-on the same cercle. In this heved of Cancer is the grettest declinacioun northward of the sonne. And ther-for is he cleped the 5 Solsticioun of Somer; whiche declinacioun, aftur Ptholome, is 23 degrees and 50 minutes, as wel in Cancer as in Capricorne. This signe of Cancre is cleped the Tropik of Somer, of _tropos_, that is to seyn 'agaynward'; for thanne by-ginneth the sonne to passe fro us-ward. And for the more declaracioun, lo here the figure. 10 The middel cercle in wydnesse, of thise 3, is cleped the Cercle Equinoxial; up-on whiche turneth evermo the hedes of Aries and Libra. And understond wel, that evermo this Cercle Equinoxial turneth iustly fro verrey est to verrey west; as I have shewed thee in the spere solide. This same cercle is cleped also the Weyere, 15 _equator_, of the day; for whan the sonne is in the hevedes of Aries and Libra, than ben the dayes and the nightes ilyke of lengthe in al the world. And ther-fore ben thise two signes called the Equinoxies. And alle that moeveth with-in the hevedes of thise Aries and Libra, his moeving is cleped northward; and alle that moeveth with-oute thise hevedes, his moeving is cleped south-ward as fro the equinoxial. Tak keep of thise latitudes north and sowth, and forget it nat. By this Cercle Equinoxial ben considered the 24 houres of the clokke; for everemo the arysing of 15 degrees of the equinoxial maketh an 25 houre equal of the clokke. This equinoxial is cleped the girdel of the firste moeving, or elles of the _angulus primi motus vel primi mobilis_. And _nota_, that firste moeving is cleped 'moeving' of the firste moevable of the 8 spere, whiche moeving is fro est to west, and eft agayn in-to est; also it is clepid 'girdel' of the first 30 moeving, for it departeth the firste moevable, that is to seyn, the spere, in two ilyke parties, evene-distantz fro the poles of this world. The wydeste of thise three principal cercles is cleped the Cercle of Capricorne, by-cause that the heved of Capricorne 35 turneth evermo consentrik up-on the same cercle. In the heved of this for-seide Capricorne is the grettest declinacioun southward of the sonne, and ther-for is it cleped the Solsticioun of Winter. This signe of Capricorne is also cleped the Tropik of Winter, for thanne byginneth the sonne to come agayn to us-ward. And for 40 the more declaracioun, lo here thy figure.