Magnetic Influence of Solar Light. 243 



effect, however, was not confined to needles that had been 

 magnetised, since it was found to apply also to unmagne- 

 tised needles, to needles of glass and copper, vibrated by 

 the force of torsion, with all of these it was found the arcs 

 of vibration diminished in amplitude more rapidly in the 

 sun's light than in the shade, in the following proportions ; 

 the terminal excess (that is, the excess of the terminal arc 

 in the shade above that in the sun, after the same number 

 of vibrations commencing from the same point in each case) 

 would by the first series of experiments, be for the magne- 

 tised needle 13° 75' ; for the copper needle 5° 24' ; and for the 

 glass needle 4° 71' — and by the second series of experiments, 

 for the magnetised needle \\\° '•> for the unmagnetised 

 needle 7° jg ; for the glass needle 6°~ ; and for the copper 

 needle 5°. ei To whatever cause," Mr. Christie remarks, " we 

 are to attribute the singular fact, that any needle will come 

 sooner to rest when vibrated exposed to the sun than when 

 screened, the great increase of effect which is observed 

 when a magnetised needle is made use of, proves, I think 

 decidedly, that the compound rays possess a very decided 

 magnetic influence." 



The experiments of Mr. Christie were repeated by Mr. 

 Zantedeschi of Pavia, who found that by exposing the north 

 pole of a needle, a foot in length, the semi-amplitude of the 



! last oscillation was 6° less than the first ; while on exposing 

 the south pole, the last oscillation became actually greater 



j than the first, a result, it must be remarked, of the most 

 extraordinary character. This observer, however, admits, that 

 he frequently met with the most inexplicable anomalies in 

 his experiments ; and in the abstract of them which I have 

 seen, they are recorded in a style of peculiar vagueness and 

 indecision. 



The results now stated appear to afford a very marked 

 confirmation to the idea of a magnetic power being resi- 

 dent in the solar rays, and yet a series of careful and 



