76 MR. J. P. JOULE ON THE LIFE AND WRITINGS 



meteor extended over a period of more than twenty years. 

 Its cause he attributes to a sudden change of temperature in 

 the upper regions of the atmosphere, giving rise to a corre- 

 sponding disturbance of the electric fluid. The attenuated air 

 is, he conceives, illuminated by these extensive movements 

 of electricity, which at the same time agitate the magnetic 

 needle in conformity with the laws of electro-magnetic action. 

 I think it must be allowed that a more intimate connexion 

 subsists between the magnetism of the earth and the aurora 

 than he seems disposed to admit, although few will, probably, 

 embrace the very artificial hypothesis of Dal ton. Mr. Stur- 

 geon shows an excellent example of the spirit with which all 

 mere hypothesis ought to be enunciated, in the concluding 

 sentence of his " Observations on the Aurora Borealis," in 

 which he says with much modesty, " It is possible, however, 

 that the theoretical views which I have here advanced may 

 be open to objections that I do not myself perceive, and may 

 require the corrections of a more diligent observer, and a 

 sounder reasoner on the facts observed." 



The last contribution I shall notice is one on a subject of 

 great scientific interest and practical importance, " the 

 electro-culture of farm crops." Many philosophers of emi- 

 nence had made the observation that plants grow more 

 vigorously when they are electrified or galvanized ; but the 

 experiments of Dr. Forster, in 1845, appear to have been the 

 earliest in which the atmosphere was employed as the elec- 

 trifying agent. He suspended a wire in the air communi- 

 cating metallically with a wire buried three inches deep and 

 surrounding the plot experimented on. He found the yield 

 of the ground, so electrified, to be considerably greater than 

 that of the rest of the field. The experiments of Dr. Forster, 

 variously modified, were repeated by Mr. Sturgeon with re- 

 sults sufficiently successful to encourage further investigation. 

 I do not know whether any further trials have been made, 

 but when we reflect upon the enormous quantity of electricity 



