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



obviates the great risk which might arise from lateral explosion 

 near the combustible or explosive materials of a cargo, and 

 particularly should any accident have occasioned any interrup- 

 tion of the complete continuity of a conductor passing through 

 the hull. 3rd. The magnetizing effects on chronometers are 

 diminished. And 4th. The labour and expense of the fitting 

 a ship with conductors are considerably lessened. I have said 

 that Mr. Sturgeon's system, however excellent, did not receive 

 much attention from the existing authorities. In addition to 

 this disappointment, he found himself involved in a dispute with 

 Mr. Harris, who had been largely successful in introducing 

 Mr. Henley's plan into the navy. The advancement of 

 science is seldom facilitated by warm controversy, and in this 

 instance it must be allowed that Mr. Sturgeon suffered himself 

 to be betrayed into stronger language than was suitable to the 

 occasion. But with respect to the scientific portion of the 

 argument, I cannot but be of opinion that he had a decided 

 advantage over his opponent. The chief subject of dispute was 

 whether a vertical conductor communicating by its lower end 

 with the earth will, when struck by lightning, produce strong 

 electric disturbance to vicinal conducting bodies not in metallic 

 connexion with the earth. Mr. Harris insists that the spark 

 which is observed to pass between an insulated discharging 

 rod and an insulated conductor very near it, is owing to an 

 excess of electricity on one coating of the ley den jar, as com- 

 pared with that on the other ; so that complete neutralization 

 not taking place, the discharging rod receives a charge which 

 it is able to communicate to neighbouring bodies. This hypo- 

 thesis is, however, entirely at variance with Dr. Priestley's 

 investigation of the phenomenon, as well as the experiments 

 of Weekes, and many others. But there can be no doubt that 

 even admitting Mr. Harris's hypothesis, the lateral explosion 

 must exist pre-eminently in a thunderstorm, the circumstances 

 of which render it almost impossible to conceive that the 

 total electricity of a cloud is just equal in amount to 



