HOLWELL CAVERN. 19 
absolutely impossible, within the limits of this paper, to 
describe the various and immense advantages which attend 
this mode of operating, which acts as a sort of comparative 
safety-valve to the electric energy, having a vast tendency 
to check an undue power, and to keep apart the attracting 
principles from too hasty a union, which would be destruc- 
tive of mineral crystallization. In nature, this is effected 
by wider or narrower veins of moist clay, termed in 
Cornwall “flookans,” and which accompany most of the 
metallic lodes. These flookans are occasionally of immense 
size, and are sometimes parallel to the lodes, but mostly 
divide them at more or less obtuse and acute angles. 
Without these flookans, or other similar checks, in all 
probability no regular erystals would be discovered in 
mines. Electricians divide all known substances into what 
they term electro-positive and electro-negative, each of which 
is composed of self repellent particeles, but attractive of 
their opposites. Thus the electro-positive particles held in 
solution are attracted to the negative pole of the voltaic 
battery, and the electro-negative ones to the positive pole. 
If a too powerful electric action be excited, the erystalli- 
zable matter will be attracted to its respective pole in a 
gelatinous or powdery form, according to its nature ; but 
no solid or definite formation will take place. If a some- 
what less action be employed, a more solid but shapeless 
mass will be obtained ; but if a feeble power be made use 
of, the consequence will be the production of erystals with 
definite, well-formed facets—exactly similar in all respects 
to natural ones of the same kind. I have now an experi- 
ment in action which has continued for eight years 
without ceasing. It consists of the passing of a feeble 
electric current through a solution of silicate of potash, 
the negative pole of the battery being connected with a 
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