26 
NOTE OK A LIGHTNING DIBCHABGE. 
On looking at the sketch it will be noticed that fire of the 
trenches start from excavations at some distance from the bases 
of the trees. Tliere were no signs o£ tunnels connoeting them 
with the bu^es of the trees, so that it would appear that the 
lightning mnst have branched before it reached the ground. 
Another point shown by the sketch is tliat the trei'S must 
have IjeoD nearly, if not quite, in the csentre of the charged urea 
of ground. This is indittated by the even way in which the 
furrows radiate from the bases of the trees. The area of ground 
covered by the furrows— that is to Bay, which is euclo&ed by 
drawing a line so as to connect their outer extremities, is about 
3,500 squaro feet in extent. 
There had been heavy rain before this particular flash 
(which oc<nirred at a few luinntess to six o'clock tii the evening) 
and the surface of the ground uiuat have been very wet. Over 
one inch of rain fell duriug the thuuder-storra, and certainly 
more than half of it fell prior tti the trees Ijeing struck. The 
rainfall for the week preceding was as follows : 
February 25th 2" 15 inches. 
26th ... 0-47 
27th 0-25 
28th Nil „ 
March 1st ... „ „ 
» 2Dd „ 
» Srd ... * „ „ 
fi 4th ... „. 
„ 5th 1-02 „ 
It will be seen that there were three wet days, with a total 
rainfall of 2*87 inches, followed by Ave dry days. Before the 
rain cx>nimeneed on the afternoon of Simday, the 5th March, the 
surface of the gronnd for some few inches in depth must there- 
fore have l)ceu fairly dry, and at the time of the flash it is 
jirobable tlrnt there was still a layer of dryish eartli iH-tween the 
wet surface and the saturated Bubsoil, It was throiigli f his top 
layer of wet Liarth that the lightning passed, and the less moist 
layer beneath it secme to have provetl an efifective insulator. 
A study of this discharge tends to ctast doubt on many of 
the ideas respecting lightning and lightning-conductors. It 
setJms to show that the charge is strictly confined U) the surface 
of the groiuid, and that the dischai^ under certain circumstances 
spreads out disruj3tively on the charged surface and dtX'S not 
peui'trate int^i the earth, altbotigh, as in this cast^, it would ctuly 
liave had U) go tlirougb a few inches of dani|i <\irth l>efore 
reaching the water-level, Insleatl of this it will hv seen that 
some of tlie furrows ran for a distance of over fifty feet, just 
