1^ Mr Watt on the Principles of' Aitractton^ 



following the moon's apparent course, like the shadow of the 

 gnomon of a dial. 



The silver-leaf only continued a vibratory movement, but the 

 arcs of vibration were evidently regulated by the position of the 

 luminary in the hemisphere. 



The movements of the feathers, and of the discs made of the 

 gold and silver leaf, are the most constant and decided. The 

 tips of the feathers are always attracted to the moon. And they 

 have frequently been observed to commence their motion a few 

 seconds after the beam has been allowed to fall upon them, in 

 whatever angle their planes may have been resting, in relation 

 to the incident ray. They have traversed, occasionally, 170° in 

 a minute ; and when the tips of the feathers came nearly oppo- 

 site to the satellite, they stopped. It is only those feathers of 

 the peacock that have a greenish hue when we look down up- 

 on their surfaces, that seem to be most attracted to the light of 

 the moon. Those feathers where the bright purplish colour 

 prevails, evince a more uncertain effect. These instruments will 

 stand for hours in a room without moving, if placed in a situa- 

 tion where the beams do not impinge upon them. 



These experiments have been often repeated, as opportunities 

 occurred, for the last six months, and with every possible pre- 

 caution. And there appears to be the greatest powers of attrac- 

 tion and repulsion in the moon's influence, from the time she 

 has completed her first octant, till she is in quadrature or gib- 

 bous. There seems less attraction when she is full, and this 

 may arise from the moon's being then in opposition, and the 

 light must be reflected from it at that time almost directly 

 against the light of the sun ; whilst, when passing through her 

 other phases, her reflected light will cross the light of the sun at 

 acute or right angles. 



It is not mere motion that has been observed in these instru- 

 ments, but a movement evidently regulated by the source from 

 which the light is emitted. 



In performing these experiments, attention must be paid to 

 the following circumstances : The cover used should be large, 

 thin, and purely transparent ; a card should be placed in the 

 centre of the stand, divided into quadrants and points, to mark 

 the progress of the revolving bar ; regard must be had to great 



