Mr Watt 071 a New Mag^ietkal Instrument. 17 



From observing, in particular, the daily variation of the baro- 

 meter and the magnetic needle, and remarking that a similar series 

 of alternate changes was more or less observable in every instru- 

 ment capable of indicating a slight alteration in the impressions 

 made on them, as the hygrometer, aethrioscope, photometer, &c. ; 

 and that these diurnal changes bore a proportionate relation to the 

 latitude in whicli the instruments were placed, or to the degrees 

 of solar influence that might exist in the regions in which they 

 were used, and of which they would partake ; and from noti- 

 cing, in coincidence with these movements, the daily expansion 

 and contraction of the petals and leaves of most plants, and that 

 the different species of the heliotropium and chrysanthemum 

 turned their corollas round toward the sun for many hours du- 

 ring the day, when the atmosphere was clear, I could not help 

 concluding, for a long time past, that what was thus partially 

 exhibited by some instruments, and more perfectly by the co- 

 rollas of plants, might be still more clearly shewn, by an instru- 

 ment constructed upon principles nearly similar to the laws 

 which regulate these motions in plants ; and that one might be 

 formed, that would, when suspended, move to the sun's appa- 

 rent course, or that would, from the attracting or repelling in^ 

 fluence of the solar rays, stand still, in opposition to the diurnal 

 revolution of the earth. 



Having an opportunity, last spring, of making some simple 

 experiments in pursuit of what had become with me rather a 

 plausible idea, I commenced, by attempting to trace the gene- 

 ral connection that appears to subsist between the solar rays, 

 electricity, magnetism, and the radiation of caloric, in as far as 

 they had any reference to the object I had in view ; to mark 

 their natural effect on plants, and to observe if metals, or other 

 substances, when placed in favourable circumstances, were not 

 susceptible of similar impressions from these general agents, at 

 least so far as to indicate by their motion when suspended, the 

 same attraction or repulsion, in respect to the sun's influence 

 that the daily alterations in the positions of the corollae of plants 

 evinced. 



In the course of those investigations, I observed, amongs 

 other things, (which it would be unnecessary here to detail. 



OCTOBER DECEMBER 1827. B 



