126 . Mr Watt mi the Principles ofAttracticyn. 



calculation, would present about a million of points to the light. 

 These facts agree with some principles generally received, as 

 establishing many coincidences between the phenomena of liglit 

 and electricity. 



Some farther observations were made on the effects of the 

 rays of light on bodies of different forms. While bodies 

 having planes, turned their edges towards the source of the 

 light, and their flat sides parallel to the line of incidence, bodies 

 of a concave shape vacillated continually in an arc of from 5° to 

 45% according to the intensity of the beam of light. Bodies of 

 a cylindrical form, crossed the line of incidence at an angle of 

 about 25°. Transparent lenses (as of amber) keep their axes 

 parallel with the incidental rays. And spherical opaque bodies, 

 when nicely suspended or balanced, have the tendency to re- 

 volve continually when the beams of the sun fall clearly upon 

 them. 



Some applications were made of the phenomena described, as 

 farther elucidating facts already known, as the attraction of the 

 leaves and petals of plants to the light, — the formation of crys- 

 tals, — the knowledge that birds and quadi-upeds seem to possess 

 of the cardinal points, as probably arising from the sensibility of 

 their hairs and feathers to the impressions of light, electricity, 

 and magnetism, and through them to the nervous system and 

 sensorium. As farther explanatory of the polarity of the needle, 

 if any current of magnetism is allowed to exist, and of the diur- 

 nal variation of the pointing and dip, as dependent on the mo- 

 tions of the sun : And from the principle thai light attracts bodies 

 or the parts of bodies that have been in the shade, and repels 

 that which has been for some time exposed to its influence, pro- 

 ducing by this means a continual revolution in bodies of a sphe- • 

 roidal form ; it is thought probable that this may be one cause 

 of the diurnal rotation of the earth and the planets. 



It has not been observed that any of these bodies indicate 

 the electrical changes of the atmosphere ; because the changes 

 in respect to them must be general, or affecting each part of 

 them equally. The silver-leaf, indeed, has sometimes a curious 

 vibratory motion ; but these vibrations are evidently regulated 

 by any beam of light falling on the disc. Two of the discs 

 suspended on two pivots, and opposed to each other, would no 

 doubt act as an electroscope. 



