569 



ever, on the directions of the ray and of the magnetic force. In 

 this respect it differs essentially from the rotatory power naturally 

 possessed by many bodies, such as quartz, sugar, oil of turpentine, 

 &c., which exhibit the phenomena of circular polarization ; for in 

 some of these the rotation takes place to the right, and in others to 

 the left. When, therefore, such substances are employed as diamag- 

 netics, the natural and the superinduced powers tend to produce 

 either the same or opposite rotations ; and the resulting effects are 

 modified according as they are cumulative in the former case, and 

 differential in the latter. 



In the concluding section of the paper, the author enters into ge- 

 neral considerations on the nature of the newly-discovered influence 

 of electricity and magnetism over light, and remarks that all these 

 powers possess in common a duality of character which constitutes 

 them a peculiar class, and affords an opening which before was 

 wanting for the appliance of these powers to the investigation of 

 this and other radiant agencies. The phenomena thus brought to 

 light confirm the views entertained by the author relative to the con- 

 stitution of matter as being spheres of power, for the operation of 

 which the conception of a solid nucleus is not necessary; and leads 

 to the presumption that the influence of magnetism on bodies which 

 exhibit no magnetic properties consists in producing in them a state 

 of electric tension tending to a current ; while on iron, nickel, and 

 other bodies susceptible of magnetism, currents are actually esta- 

 blished by the same influence. 



The author states that he is still engaged in the prosecution of 

 these inquiries. 



On the Action of the Rays of the Spectrum on Vegetable 

 Juices : " being an Extract from a Letter by Mrs. M. Somerville to 

 Sir John F. W. Herschel, Bart., dated Rome, September 20, 184-5. 

 Communicated by Sir John F. W. Herschel, Bart., F.R.S. 



In the experiments of which the results are here recorded, the solar 

 spectrum was condensed by a lens of flint glass of seven inches and 

 a half focus, maintained in the same part of the screen by keeping a 

 pin-hole or pencil-mark constantly at the corner of the red rays, 

 which were sharply defined by being viewed through blue spec- 

 tacles ; and the apparatus was covered with black cloth in order to 

 exclude extraneous light. Thick white letter-paper, moistened with 

 the liquid to be examined, was exposed wet to the spectrum, as it 

 was found that the action of the coloured light was thus rendered 

 more immediate and more intense, than when the surface of the 

 paper was dry. 



The action of the spectrum at the junction of the lavender with 

 the violet rays was found in soiHe cases to be different from what it 

 is with either of these colours separately, indicating a break in the 

 continuity of action, and suggesting the idea of a secondary spec- 

 trum. In many instances the yellow and green rays exert a power- 

 ful influence on vegetable substances, an influence apparently un- 

 connected with heat; for the darkening is generally least under 



