134 Mrs. M. SoMERViLLE on the magnetizing power 



they were free from magnetism. The needles were placed 

 in various directions in the plane of the magnetic meridian^ 

 sometimes in the angle of the dip, sometimes perpendicular 

 to the magnetic meridian, and also at various angles with 

 regard to it. In some cases the heads of the needles were 

 exposed in place of the points, to the violet rays. Perhaps it 

 might have been expected that the influence would have 

 been greater in those instances in which the needles were 

 placed in the plane of the magnetic meridian, and at the 

 angle of the dip ; and, consequently, polarity might have 

 been expected to take place in a shorter time under these 

 circumstances ; yet in fact there seemed to be no difference ; 

 most of the needles became magnetic, some in longer, others 

 in shorter periods, varying from about half an hour to four 

 hours, but depending on circumstances which I have not yet 

 been able to detect, further than that a number of results 

 induced me to believe, that the experiments were more suc- 

 cessful from ten to twelve, or one o'clock, than later in the 

 day. The portion of the needle exposed was almost always 

 a north pole, whether it pointed upwards or downwards. In 

 a few instances in which the contrary occurred, it may possi- 

 bly have arisen from some previous disposition in the needle 

 to magnetism, too shght to be observed. 



The distance of the needle from the prism was frequently 

 varied by fixing the needle to the wooden pole of a fire- 

 screen, but without material variation in the effect. I found 

 it unnecessary to darken the room ; it was sufficient to place 

 the prism so as throw the spectrum on any place out of the 

 sun's rays. 



My next object was to endeavour to ascertain whether any 



