320 SIR JOHN HERSCHEL. 



5. Reversal of the effect with that of the cause. 

 He adds, that we are not to deny the existence 

 of a cause in favour of which we have a unani- 

 mous agreement of strong analogies, though it 

 may not be apparent how such a cause produces 

 the effect. (Discourse on the Study of Natural 

 Philosophy, section 145 and 148.) 



The above general rules apply with great 

 force to the connexion between temperature and 

 the phenomena of lightning. 



1. It has been shewn, in accordance with the 

 first rule, that a certain range of solar tempera- 

 ture is indispensable to the existence of lightning, 

 which are therefore invariably connected together 

 as antecedent and consequence, or cause and effect. 



2. It has also been shewn, in conformity with 

 the second rule, that in the absence of condensa- 

 tion and precipitation of vapour there is no light- 

 ning : 



3. That other things being equal, the amount 

 of evaporation, condensation, and lightning, are 

 increased and diminished with the augmentation 

 and decrease of temperature. 



4. That the quantity and splendour of this 

 wonderful meteor are proportional to the accumu- 

 lation and intensity of solar heat, from the equator 

 to the poles and 



5. That the effect is reversed on passing from 

 the regions of perpetual cold to the torrid zone, 

 and from winter to summer. 



