all known Substances to the Magnetic Influence, Sfc. 331 



directive force of a magnetic bar, then, we might infer, that the 

 combined action of two or more equal and similar magnets, 

 ouglit to be equivalent to the amount of the tangents of their 

 several deviations. But, although the results of many experi- 

 ments are found to approximate the ratio indicated by this co- 

 rollary, yet in almost every instance the tangent of the angle of 

 deviation produced by different bars in juxtaposition, falls short 

 of the amount of the tangents of their individual deviations. 

 This general fact suggested the idea, that, notwithstanding tlie 

 bars were not placed in contact, when their combined influence 

 was tried, yet their very proximity might operate to the dimi- 

 nution of their influence. And this, on trial, was found to be 

 the case, especially with the pair of two feet magnets (B), tem- 

 pered only at the ends. The deviations produced by the two 

 bars separately, at a given distance from the compass, were 

 6° 15' and 6° 3(y, amounting together to 12° 45', or, reckoning 

 the sum of their tangents, to 1^° 36'. When the same bars 

 were presented simultaneously to the compass, (at the same dis- 

 tance as before), parallel to each other, and 12 inches asunder, 

 their combined action- was 12° 20' ; at 3J inches asunder the 

 deviation produced by them was 12° 0' ; at I inch, 11° 30' ; at 

 :Jth of an inch 11° C. Being again separated to 3 J inches apart, 

 their action was now 11° 30' ; and to 12 inches it increased to 

 11° 55', — indicating, however, a loss of power by their proxi- 

 mity from tangents 12* 20' to 11° 55', or of about /^th part of 

 their force. Their separate action was now found to be 6° 5' 

 and 6° 0', amounting to 12° 5'. The amount of the tangents 

 of these two deviations observed separately, is 21168 ; whilst the 

 tangent of the two, taken in combination at 1 2 inches distance, 

 is 21104, being very nearly the same. Part of the loss of power 

 in this experiment, is to be ascribed to the imperfect tempering 

 of this pair of magnets, which, as I have stated, were not tem- 

 pered throughout, but only at the poles. Still we find, that, 

 when placed very near, though not in contact, their united ac- 

 tion was considerably diminished, but not permanently, so that 

 their power in juxtaposition, at the distance of ^th of an inch 

 from each other, was less than when they were a foot asunder, 

 in the proportion of the tangents of 11° 0', and 11° 55\ — indi- 



