CHAP, iv.] ELECTRICITY AND MAGNETISM. 253 



this Lesson frequent differences between the behaviour 

 of positive and negative electrification. The striking dis- 

 similarity in the Lichtenberg's figures, the displacement 

 of the perforation - point in Lullin's experiment, the 

 unequal tendency to dissipation at surfaces, the remark- 

 able differences in the various forms of brush and glow 

 discharge, are all points that claim attention. Gassiot 

 described the appearance in vacuum tubes as of a force 

 emanating from the negative pole. Crookes's experi- 

 ments in high vacua show molecules to be violently 

 discharged from the negative electrode, the vanes of a 

 little fly enclosed in such tubes being moved from the 

 side struck by the negative discharge. Holtz found that 

 when funnel-like partitions were fixed in a vacuum tube 

 the resistance is much less when the open mouths of the 

 funnels face the negative electrode. These matters- are 

 yet quite unaccounted for by any existing theory of 

 electricity. 



The author of these Lessons is disposed to take the following view on this 

 point : If electricity be really one and not two, either the so-called positive 

 or the negative electrification must be a state in which there is more electricity 

 than in the surrounding space, and the other must be a state in which there 

 is less. The student was told, in Art. 6, that in the present state of the science 

 we do not know for certain whether "positive" electrification is really an 

 excess of electricity or a defect. Now some of the phenomena alluded to in 

 this Article seem to indicate that the so-called "negative" electrification 

 really is the state of excess. In particular, the fact that the rate of dissipa- 

 tion of charge is greater for negative electrification than for positive, points 

 this way ; because the law of loss of charge is the exact counterpart of the 

 law of the loss of heat, in which it is quite certain that, for equal differences 

 of temperature between a body and its surroundings, the rate of loss of heat 

 is greater at higher temperatures than at lower ; or the body that is really 

 hotter loses its heat fastest. 



LESSON XXIV. Atmospheric Electricity. 



3O1. The phenomena of atmospheric electricity are 

 of two kinds. There are the well-known electrical pheno- 

 mena of thunderstorms ; and there are the phenomena 



