288 Researches in the Theory and Calculus of Operations. 



their opposing directions : a north and south, determined 

 * by the Sun and the poles of the earth; an east and west, 

 determined by the rising and setting of the Sun; and an 

 ascending and descending pair of forces, due to the action 

 of the emanation from the centre of the earth (force of gra- 

 vity), as opposed by the centrifugal force generated by ro- 

 tation. When material substances have been liquified by 

 warmth or heat and subsequently left to cool in quiet, the 

 gentle but pertinaceous forces alluded to make themselves 

 felt by the yielding atoms, which may thus be deformed, 

 each element according to its peculiar density, into sphe- 

 roidal or ellipsoidal shape. The lines of maximum and 

 minimum density of an atom, which will become the crys- 

 tallagrophic axes of the accretion, may be forced into incli- 

 nation to one or all three of any set of perpendicular axes, 

 and thus give rise to the various shapes of crystals formed 

 by nature or artificial chemical conduct; the planes of cleavage 

 of which would seem to occur where the atomic forces just 

 meet with touch and mutual equilibrium, or rather form 

 nodal planes across which the atomic forces are transmitted 

 from layer to layer. A certain number of atoms, peculiar 

 in different substances, unite in linear groups to form the 

 laminae of the crystal. The direction of greatest atomic den- 

 sity, whether produced by crystallization or by artificial 

 pressure, appears to determine the distinction .between 

 paramagnetic and diamagnetic substances. 



26. As the rising of the Sun first touches a meridian 

 (here regarded as an atmospheric ring) upon its eastern 

 horizontal trace, the heating effects of the rays travel in a 

 hclicoidal path around the centre of the ring, towards the 

 equator from the poles. The magnetised needle consists of 

 a small cylinder or bar generally of steel, the particles or 

 molecules of which have been brought into a state of heli- 

 coidal tension around the axis of the bar; so that when 

 freely suspended by its centre of gravity, the rotative ten- 



