all known Substances to the Magnetic Influence^ &^c. 113 



amply verified, and, by which an increasing influence, under 

 improved arrangements, was progressively produced. 



The first experiment in which any very great distance was 

 attempted, was made with four straight bar-magnets of two feet 

 in length each (two of them, however, were very weak, and 

 added little to the result), with a view of endeavouring to con- 

 vey the magnetic influence through my own house. The com- 

 pass, in this instance, was placed outside of the northern, or 

 main back-wall, a little above the level of the dining-room floor, 

 and the magnets were placed on the south side of the southern 

 or main front-wall, a little below the level of the dining-room 

 floor, — so that the magnetic influence, if it should aff*ect the 

 compass, might pass, not only through the intermediate space 

 of 25 feet 6 inches, but, at the same time, through the two prin- 

 cipal walls of the house, and obliquely through all the joists of 

 the floor, with other interposing substances. In order to render 

 the compass as susceptible as possible, the directive force of the 

 earth's magnetism was very greatly diminished by a neutralizing 

 magnet placed near it ; whilst, in each experiment, the magnets 

 on the opposite front of the house were simultaneously turned, 

 with their analogous poles the same way, so as to influence the 

 compass by the sum of their action. Three sets of experiments 

 were now made, when the results gave an amount of deviations 

 of 0° 2(y, 0° 15', and 0° 15'. Whilst the compass, with its neu- 

 tralizing and directing bar were undisturbed, the magnets were 

 brought round into the back garden, and placed at the distance 

 of 25 feet 6 inches from the compass in the opposite direction, 

 in which there was no interposing object ; — the deviations now 

 produced by changing the poles of the magnets simultaneously, 

 were, in this position, very nearly the same as before, being, on 

 each of three successive experiments, 0° 15'. This was decided 

 evidence of the great extent at which the directive power of the 

 magnet is capable of influencing the compass, and indicated 

 that the measure of distances, even within a quarter of a degree 

 of deviation, or less, might be accomplished with considerable 

 precision. 



On subsequent trials, however, a visible action on the com- 

 pass was produced by the influence of a pair of two feet mag- 

 nets only, at much greater distances. 



VOB. XIII. NO. XXV. JULY 1832. H 



