THE BAR-MAGNET iii 



number as polar regions or poles. They are, so to speak, points of distribution and convergence. They are also 

 foci or points of intensity. 



In studying Fig. 1, Plate Iv., which represents the effect produced by the contact of a lodestone or natural 

 magnet with iron-filings equally distributed on a horizontal sheet of white paper, it is important to note the general 

 appearance of radiation so well seen in cross sections of the stems and other parts of plants, and in cross sections 

 of the muscles, bones, teeth, horns, and other parts of animals. It is also important to observe the first traces 

 of curve, and circular formations, in the several parts of plants and animals. Compare with Plates xxii., xxiv., 

 and xxvii. 



The idea presented by the contact of the lodestone with the iron-fihngs is that of a power radiating its energy 

 in more or less straight lines, stellate-fashion, and in more or less curved lines, concentric-fashion. Both the 

 radiating and concentric forms of energy occur in plants and animals, and the two kinds of energy are to be 

 credited with the radiating and concentric arrangements so common in plants and animals, and to which plants 

 and animals largely owe their symmetry and their strength. The radiating and concentric arrangements are also 

 seen in crystals (compare Plates i. and ii.). The radiating and concentric arrangements in question point to a 

 common law of construction in crystals, plants, and animals. 



From what has been stated it will be apparent that the iron-filings equally distributed on a horizontal sheet of 

 white paper are acted upon and influenced by the lodestone or natural magnet. The fiUngs form the so-called 

 " magnetic field " ; this consisting of the space to which the influences of the magnet extend. As the external 

 surface of the magnet and the magnetic influences exerted thereby only have to be considered, it is permissible to 

 speak of the magnetic field as confined to one or more planes. As, however, the interior portions of the magnets 

 and the magnetic influence exerted by them are also to be considered, it follows that the magnetic field must be 

 enlarged, the field of the magnet being extended in three directions. As a matter of fact, the magnetic field in the 

 extended or ultimate sense surrounds or invests the magnet as a whole. It is therefore best represented as a spherical 

 space with the magnet in the centre ; the lines of force emanating from the magnet radiating into space to a 

 practically unlimited extent. 



As the polar regions or poles of the lodestone or natural magnet are unequally distributed, from irregularity of 

 shape and other circumstances, it is necessary to direct and concentrate the magnetic influences within hmited areas. 

 This is best done by the employment of soft iron shields and rods which are readily permeable to magnetism. The 

 iron shields and rods are applied to the polar regions of the lodestone ; the polarity being transmitted to the 

 exterior of the so-called " pole-pieces " in an intensified form. 



When the pole-pieces are applied to iron-filings evenly distributed on a horizontal sheet of white paper a lines 

 of force picture is produced, as shown at Fig. 2 of Plate Iv. The fines of force picture is remarkable for its symmetry, 

 and for the locafisation of the poles. There is radiation of the iron particles round each pole as a centre, and between 

 the poles the iron particles are disposed in what are virtually concentric lines. The radiating and concentric 

 arrangements indicated in Fig. 1, Plate Iv., reappear in a slightly modified form, and produce arrangements met 

 with in crystals, plants, and animals. 



The pole-pieces of the lodestone may be connected and the magnetic circle closed by applying a band or bridge 

 of soft iron, known as the keeper, to them. In this case the magnetic properties of the lodestone are conserved. 

 The keeper aggregates and transmits through it the lines of force which pass from pole to pole. It adheres to the 

 pole-pieces and so overcomes gravity. 



As will be seen, the magnetic properties of the lodestone may be intensified, directed, and conserved by the 

 aid of the pole-pieces and keeper. Whatever the nature of the magnetic power, it is evidently non-material. This 

 follows because the finest and most sensitive scales or balances fail to detect any increase in weight of substances 

 after magnetisation. In other words, the substance magnetised is of exactly the same weight as the substance 

 unmagnetised. Magnetisation can only consist of a: rearrangement of the matter already existing in the substance, 

 or in giving to the particles of the substance, and those surrounding it, some kind of motion, most probably of 

 a cycUcal or rotatory nature ; the motion not affecting the magnet as a whole, but only its component parts. 



§23. The Bar-Magnet. 



The production of fines of force pictures is facilitated by the employment of artificial magnets, as these can be 

 made of suitable sizes and of convenient shapes. The simplest is the bar-magnet. This consists of an elongated 

 bar of steel magnetised by stroking it with the pole-piece of a lodestone in the same direction forty or fifty times. 

 Its magnetic properties are most marked at, and indeed almost exclusively confined to, its free ends ; these constituting 

 its poles. The bar-magnet, when apphed to iron-fihngs evenly distributed on a horizontal sheet of white paper, as 



