454 Analyses of Books. [June, 



sion of the work, his papers, " On the Effects produced in the 

 Rates of Chronometers by the Proximity of Masses of Iron ;" and 

 " On the anomalous magnetic Action of hot Iron between the 

 bright and blood-red Heat," first published in the Phil. Trans, 

 for 1821 and 1822; and already noticed in the Annals. 



After describing the additional experiments and observations 

 on the local attraction, which fully confirm his former conclu- 

 sions, Mr. B. concludes the consideration of that subject in the 

 following manner : 



" Such is the present state of this method of correcting the 

 local attraction or vessels ; and here I must take my leave of the 

 subject, on which I have already bestowed much time, and 

 have incurred some pecuniary charge in carrying the experi- 

 ments into execution. I have, I trust, shown very clearly by 

 the results reported in the preceding part of this section, parti- 

 cularly in those of the Barracouta, that the errors arising from 

 the local attraction are of such a nature and amount, as to 

 require correction. I have also explained a simple method by 

 which this is proposed to be effected ; and I have given testi- 

 monials of its efficacy, in a case where it was submitted to trial 

 during a voyage of sixteen months." 



The second part of this Essay contains " A Theoretical Inves- 

 tigation of the Laios of Induced and Terrestrial Magnetism," 

 consisting of the following sections : " I. Investigation of the 

 laws of magnetism peculiar to iron bodies — Of the horizontal 

 needle — Of the dipping needle — General results. II. On the 

 change of magnetic intensity of a needle as affected by iron 

 spheres. III. On the magnetic action of bars of iron — Supple- 

 mentary experiments on the action of iron plates. IV. Appli- 

 cation of the preceding formula? to the magnetism of the terres- 

 trial sphere. V. On the situation of the terrestrial magnetic 

 axis, and on its annual motion." 



Mr. Barlow founds the investigation in the first section upon 

 the following hypothesis, which is a modification of that pro- 

 posed by Mr. Bonnycastle in the Philosophical Magazine, 

 vol. lv. p. 132, 446. 



" 1. Magnetic phenomena are due to the existence of two 

 fluids in a greater or less degree of combination, and such, that 

 the particles of the same fluid repel, and those of an opposite 

 nature attract, each other. 



" 2. These fluids in iron bodies exist naturally in a state of 

 combination and equilibrium, till that state is disturbed by some 

 exciting cause. 



" 3. But if a body, already magnetic, i. e. one in which these 

 fluids are held in a state of separation, be brought within the 

 vicinity of a mass of iron, such as is supposed above, the concen- 

 trated action of each fluid in the magnetized body will act upon 

 the latent fluids in the quiescent body, by repelling those of the 

 same, and attracting those of the contrary kind, and thus impress 

 upon the latter a temporary state of magnetic action, which will 



