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XLII. On the Production of Statical Electricity by the Action 

 of Heat and Light. By Prof. G. Melander *. 



F j^HE problems of atmospheric electricity were among the 

 A first to occupy the attention of investigators of elec- 

 trical phenomena. {Since the classical experiment of Franklin 

 in 1751, several physicists have shown that there exists an 

 electrical field over the surface of the earth in clear as well 

 as in cloudy weather. Experiments on atmospheric elec- 

 tricity were at first carried out by means of kites, which 

 occasionally reached considerable heights and collected 

 electricity from the clouds. Afterwards balloons were em- 

 ployed and observations were made on the ionization of the 

 air. These experiments showed that the air is nearly always 

 electrically charged, and that in fine weather the air is 

 positively, and the earth negatively charged. That a connexion 

 exists between the intensity of sunshine and the phenomena 

 of terrestrial magnetism, appears to me probable from my 

 experiments on illuminated magnets, and the question arises 

 whether the rays of the sun might not be the indirect cause 

 of the magnetism of the earth, i.e. whether the earth-currents 

 might not be the effect of sunshine. 



In order to investigate this question I procured a Dolezalek 

 quadrant electrometer. This electrometer is so sensitive 

 that by using sufficiently fine quartz fibres a deflexion of 

 17 mm. per millivolt maybe obtained, but it is not advisable 

 to use fibres of smaller diameter than '004 mm., as then 

 the needle, owing to the friction of the air, takes a very long 

 time to come to rest. The needle, which is of silvered paper, 

 was charged to a potential of 89 volts by means of a 

 water-battery. The charge was led to the needle through 

 the quartz fibre, which was rendered conducting by dipping- 

 it in a solution of chloride of magnesium. One pair of 

 quadrants was connected to earth, and the other to a small 

 piece of brass, which was hung free in the air with an 

 insulated wire. The charge on a body may be easily measured 

 by bringing it near the brass piece and observing the de- 

 flexion of the electrometer, and the sign of the charge may 

 be determined in the usual way. In order to avoid all 

 external disturbances the apparatus was completely enclosed 

 in a cage of fine wire gauze. The arrangement of the appa- 

 ratus is shown in the accompanying figure. The cage and 

 the zinc plate ZZ on which it was placed were connected to 

 earth. The door TT allows the body whose electrification is 



* Communicated by the Author. 



