246 Magnetic Influence of Solar Light, 



Section III. — On the magnetic action of the light, trans- 

 mitted through different coloured media. 



Section I. — On the magnetic action of uudecomposed light. 



In proceeding to detail the experiments of this section, 

 I would first describe the apparatus employed. The needles, 

 or rather cylinders, used were of soft steel, of various lengths 

 and diameters, as noted particularly in the subsequent 

 tables, and having surfaces brightly polished. Each needle 

 was fitted into a brass wire stirrup made in the following 

 manner : a piece of very thin wire about two inches in length 

 is bent double, a small loop is then formed by twisting 

 the bent wire twice or thrice, leaving the ends about three- 

 quarters of an inch long each — the wire is then placed on 

 the centre of the needle, the right hand end seized by a 

 piece of pincers and wrapped round the needle, and the 

 same being done with the left hand end, the stirrup is com- 

 plete. To the loop of the wire there were attached a few 

 filaments of silk, for the purpose of suspension, the length 

 of which, throughout the experiments, was 13 inches. The 

 detached extremity of the suspending filament was inserted 

 into the split made in a piece of straw, and on the needle 

 being introduced within a large glass shade, to protect it 

 from the wind or other disturbing causes, the straw was 

 placed across the aperture in the top of the shade, and thus 

 supported the needle during its oscillations. At the bottom 

 of the glass shade was placed a graduated circle, over 

 which the needle oscillated, and by which the oscillations 

 were regulated. 



Method of observation and adjustments. — The method of 

 observation employed throughout this section, was to ob- 

 serve the time required to perform a certain number of 

 oscillations before and after exposure to the sun's light. 

 Since the same dynamical laws are applicable to needles 

 oscillating under the influence of magnetic power, as to pen- 



