440 On tit Tinninat'tons of CcnduBors for Lightning, 



Under thefe conGdcrations, the condu£lor terminated by a ball might be thought pre- 

 ferable to one terminated by a point : but when we recollect that mofk of the metallic fub- 

 llances which belong to buildings are generally terminated in edges and points; that-thejr 

 have the f.imc influence as the point upon the condu£lor; that their operation may be at- 

 tended with more danger, and that they may extend their influence beyond that of n con- 

 <fu£ior terminated by a ball ; we may therefore conclude, that the height to which a pointed 

 conductor is cenerally raifed above thi' other metallic fubftances belonging to a building, 

 when compared with the vatl diftanccs at which lightning can zGt, will not increafe, in any 

 great degree, the danger to which a building may be expofed under the circumftances exhi- 

 bited in the fecond cafe of this experiment : and therefore conductors that are terminated by 

 points are more likely to produce the good efPefls cxpeded from them than thofe which are 

 terminated by balls. 



Thefe confiderations upon the effeds th:'.t may be produced by the joint operations of po- 

 Ctive and negative electricity, have, thu'' ir, been confined to what may happen within a 

 fpace occupied by a building ; but they may be extended to much greater fpaccs upon the 

 furface of the earth. A condudtor may be flruck by lightning, and (if the lower furface of 

 the body of charged air extends over no pan of the building) may convey the lightning in- 

 to the earth, without the leaft mifchief being done to the building ; but when the lightning 

 arrives at the lower extremity of the conductor, there is no proof that by its union with the 

 earth it becomes decompofed. That decompofition cannot happen until it becomes united 

 with its oppofite electricity, which may be att-jched to a bodv of earth or fubftances far re- 

 moved from the condu£tor. The ligl-.tning will therefore cominue its operations until it ar- 

 rives at the place where the oppofite electricity is prefent, and in its pafl'age will occaGon 

 much mifchief if it does not meet with good conducing fubftances. • 



The accidents which have been known to ha: pen at a diftance from the place which was 

 feen to be (truck by lightning, have been afcribed (by reafoning according to the theory of 

 Dr. Franklin) to what is called a ri/iirnirig Jiroke\ but it might, with an equal degree of 

 probability at leaft, be afcribed to the object to which the accident happened being within 

 the circuit which the lightning makes between the oppofite furfaces of a body of charged ain 

 London, Nov. 2<), 1797. HENRY HALDANE. 



In addition to what has been already written two figures are annexed (Plate XVIII). The 

 flrlt is 3 drawing to reprefent a building fumilhed with a condu(Slor, which is fuppofed 

 to bt (truck by lightning. 



The fecond is a plan of apart of the ele£lrical apparatus, arranged as defcribed in the 

 ftcond Cafe of thefe Experiments. 



References to Fig. L 



A A reprefents the upper furface of a body of charged air. 



B B B the lower furface of the fame body of charged air, which is attached to the earth 

 and terreftrial bodies, and in an oppofite (late of elc£tricity to that of the upper furface A. A. 



This lower furface may extend to the places marked i, a, 3 ; that is, the limit of charged 

 air may be reprefented by the dotted lines A i, A 2> A 3, as defcribed in the three Cafes of 

 the Experiment. 



C the condu£lot. 



C F The 



