[ 22 5 ] 
and expenfive however, to with to fee often rc- 
If the ereding of an apparatus of this fort fhould 
become general in countries where thunder (forms are 
frequent and often attended with mifchief, though 
damage (hould really be averted by it, the operation 
of the apparatus would be unfeen, and therefore un- 
known, unlefs in fuch rare inftances as that men- 
tioned by Mr. Kinnerfly. To make its effeds ap- 
parent, as has been hinted to me by Dr. Heberden, a 
very defervedly eminent phyfcian here, if chains are 
employed as metallic communications, inf ead of wires 
or rods, whenever the lightning comes near enough 
to affed the apparatus in a confiderable degree, it will 
without mifchief be vifible in the dark, by itsfpark- 
Jing and flapping in its paffage, at the links of the 
chain. 
The effeds of the apparatus may be obferved in 
another manner. If the metallic communications are 
by the means of a wire or lingle rod, there may be, 
in fome part of its length, in any place convenient 
for obfervation, a fpaceleft where the metal is difcon- 
tinued ; but this fpace fhould not exceed two inches. 
The two extremities of the metal at this interruption 
fhould be furnifhed with brafs knobs not lefs than an 
inch in diameter. By this method, though the effeds 
of the apparatus would not be confiderably leffened, 
they might be obferved. For at times, when no 
lightening was vifible, but when clouds replete with 
it came near the apparatus, or rain from them fell 
upon it, there would be a flapping from one of the 
brafs knobs to the other. When indeed the light- 
ning was near, there would not only be this flapping; 
but, if the caufe was great, a dream of fire would be 
Vol. LIV. Gg feen 
