20 Mr Watt on a New Magnetical Instrument, 



parted by the concentration of any of these bodies. When the 

 rays of the sun were collected into a focus by a lens, and made 

 to impinge on the needles, they moved rapidly on the water 

 from the solar beam. The same effect was produced by a piece 

 of metal heated, and held over the points of the needles. Elec- 

 tricity also seemed to attract or repel them, in proportbn to its 

 force. 



I also found, that, if the small seeds of plants are dried, and 

 laid upon any good electric, which has been smartly rubbed, 

 and the poles of a strong horse-shoe magnet is moved slowly 

 over the seeds, they will spring from the electric to the magnet 

 more readily than to any other body not magnetic. 



Observing, therefore, a considerable similarity between the 

 effects of all these imponderable bodies on plants (the petals of 

 which contain iron), and on iron, I formed a thin piece of silver- 

 plated copper into the shape of the calyx of a flower, and fitted 

 a thin circle of cork to the edges of the copper cup. Into this 

 circle I fixed twenty needles, highly magnetic, at equal distan- 

 ces from each other, in the form of the extended radii of the 

 circle (as represented by the first sketch), with all their south 

 poles pointing outwards, and their north poles directed to the 

 centre of the circle, (destroying by this arrangement their power 

 of indicating their polarity, in respect to the earth). I suspend- 

 ed this by a very delicate filament of silk, from the centre of a 

 glass cover, excluding any current of air, by fixing the cover to 

 a smooth board by wax. I exposed this star of needles to the 

 influence of the solar rays, and it continued first to revolve, and 

 then to vacillate, for the most part of the day ; exhibiting, 

 however, when it ceased to revolve, a movement corresponding 

 to the position of the earth in reference to the sun, as the sun 

 was always found opposite to the centre of the arc of vibration. 

 After repeating the experiment for four or five days, the vibra- 

 tions diminished in the extension of the arc they described ; and 

 the movement corresponding to the rising and setting of the 

 sun was more regular and certain. The first combination of 

 this sort which I made was very light. The next I formed in- 

 tentionally of an ounce weight, to mark the extent of the influ- 

 ence of the solar rays. It was formed in the same manner as 

 the first, with the addition of a circle of zinc round the copper 



