F. Dellmann on Atmospheric Electricity. 417 



electric uiiclei- such circumstances. Wlien rain commences, the 

 drops are generally negatively electric like the air. In still air 

 the tension of atmospheric electricity is much less variable than 

 in strong winds : it varies most quickly when the electricity 

 passes from the negative to the positive state, or vice versa. At 

 4-20 P.M. on the 14th of December, the tension during a very 

 slight shower of rain was —918-7. Seven minutes afterwards it 

 was 0, and the rain had quite ceased. Two minutes afterwards, 

 when a little rain again fell, it amounted to +41-5 ; two minutes 

 after this, however, it rose to 281-4, when rain had ceased. 

 Three minutes later the tension was 547-5 ; and after another 

 interval of four minutes it rose as high as 831. At 2 p.m. on 

 the loth of December, the tension changed in a few minutes 

 from C6-5 to —447-1. Such examples occur in all months, and 

 particularly in rain and storms. 



The electricity of the clouds and that of the air are so related 

 to one another, that a considerable amount of cloud or storm- 

 electricity is accompanied by a considerable tension in the at- 

 mospheric electricitjr, though the latter may exist without the 

 former. The electricity of the air may be very great for hours 

 or even for days, without the least trace of a storm being pre- 

 sent ; this is always the case on cloudy wintry days, particularly 

 when there is a north-west wind. On a single occasion, between 

 4^ and 5^ p.m. on the 16th of November, after the air had been 

 found in a high degree negatively electric at 2 p.m., a thick mist 

 was suddenly dissipated by a storm which was announced by 

 negative electricity, though generally positive electricity mani- 

 fests itself with a thick mist. 



It is only free air, not in contact with objects on the earth's 

 surface, that exhibits electricity with the above-described appa- 

 ratus ; no trace of electricity can be detected in the house, even 

 when a strong tension exists outside. This appears to be at 

 variance with a fact above recorded touching the smaller loss of 

 l)ositive electricity; nevertheless the positive electricity in the 

 house maybe too small for the apparatus to indicate. 



During a fire whose smoke, almost exactly in the shape of an 

 arch, drew near the place of observation, the tension of 149 

 rose in a few minutes to 383 ; it then diminished again as the 

 fire decreased, so that 17 minutes after the first tension it still 

 amounted to 250-7. On the rekindling of the fire the tension 

 rose again a few times until an hour and a half after the fire 

 broke out; and after it had been long extinguished, the tension 

 still amounted to 120. The site of the fire was ^th of a mile * 

 distant from the observatory. From the above it follows that in 

 a town where there arc many smoking chimneys, no eleclricul 

 • The measiirenu-nts are all .icconliiip; to Prussian units. 

 rhil. M(t<j. S. 4. Vol. 18. No. 122. Dec. 1859. 2 E 



