48 Analyses of Books. [July, 



Chap. VIII.— Of Magnetism. 



Magnetism has been always considered as analogous to elec- 

 tricity. Its phenomena of course must be the result of the action 

 of the same kind of forces. There is only one difficulty that 

 occurs to oppose our concluding that the electric and magnetic 

 forces are the same, and that is, that electric bodies act upon 

 magnetic bodies as if they were not endowed with any peculiar 

 force. Our author not being able to deny the existence of this 

 difficulty, endeavours to elude by pointing out some phenomena 

 in electricity itself of somewhat an analogous nature. 



He notices in this chapter an opinion of Ritter, which has 

 since been confirmed ; namely, that the aurora borealis is a 

 magnetical phenomenon. Hansten, a Danish mathematician, 

 has proved that the earth has four magnetic poles, as Halley had 

 conjectured. He has found that the aurora borealis appear 

 always in their greatest intensity round these four poles, and 

 that the radii are parallel to the magnetical inclination. 



Chap. IX. — Considerations on the Theories in the Experimental 

 Sciences, and Synoptical Vieiu of' the Principles of the Dynamic 

 System. 



After some very judicious observations on the way in which 

 the experimental sciences advance, and on the necessity under 

 which we are to connect the facts in them by means of theory, 

 our author terminates his work by the following epitome of the 

 theory which he has endeavoured to establish in it. 



Two opposite forces exist in all bodies, and of which they 

 never can be altogether deprived. Each of these forces has an 

 expansive and repulsive action in the medium in which it predo- 

 minates ; but they attract each other, and produce a contraction 

 when they act on each other. The most free action of these 

 forces produces the electric phenomena. These forces may be 

 condensed, retained in a certain space, and even rendered 

 entirely latent, by their attraction for each other. 



Their passage from one point to another is so much the more 

 difficult the greater their quantity and the smaller their intensity 

 is. But when they are at once feeble, in great quantity and 

 latent, or almost latent, they cease to be transmitted even by 

 contact, if this change is not favoured either by the intervention 

 of very intense forces, or by an augmentation of the conducting 

 power. 



It is in this state when the forces are too latent to produce the 

 electric phenomena that they constitute the chemical properties 

 of bodies. The way in which these two forces are disposed, and 

 the state of cohesion and of conductibility which proceeds from it, 

 as well as degree of preponderance of one of these forces over 

 the other, form the principal differences which exist between 

 bodies. The quantity of the preponderating force is always very 



