HOLLOW LIGHTNING CONDUCTOR CRUSHED BY THE DISCHARGE. 133 



Fig.l 



Description of the Conductor. 



Fig. 1 is a sketch to scale of the 

 upper portion of the lightning con- 

 ductor, the parts drawn in con- 

 tinuous lines shewing the pieces 

 which have been preserved, a b 

 represents the pipe, whose dimen 

 sions have been already given. At 

 a and b the pipe was sweated on to 

 solid rods, the upper one being 

 attached to the ball and the lower 

 one to a right angled piece to which 

 the main conductor was attached. 

 The folding is most pronounced at 

 b just below the end of the solid 

 rod ; it is not quite symmetrical 

 as the pipe is stiffer at the lap joint. 

 Folding is also shown at a just 

 above the end of the solid rod ; at 

 this point the pipe was fused. The 

 greater portion of the pipe from c 

 to a was unaltered in shape, its 

 section remaining circular. After 

 the fusion at a the lower part of 

 the conductor fell away but the 

 pipe remained vertical throughout 

 its length, attached to the chimney 

 by the two holdfasts shown. Photo- 

 graphs of the part b c are given in Plate in., and the dia- 

 grams B and C (fig. 1) represent enlarged sections of the 

 conductor on the lines b and c respectively. 



The surface of the upper part of the tube is covered with 

 little pit marks from about 0*1 to 0*5 mm. in diameter and 

 0*02 mm. deep. We are unable to say whether these marks 



