During the kite experiment, Benjamin Franklin put an iron stalk on the kite. As he wanted to prove the similarities between lightning and electricity, that was an exellent reasoning.
Indeed, a law regarding electricity was discovered after Franklin’s life-time. It tells us the smaller an object is, the stronger its electric field is near it. The law involved is Gauss’ law.
Where E is the value of the electric field in a point near the sphere,
1/(4πε) is a constant ( also called k),
Q the total electric charge of the sphere,
and r the radius from the source to the point.
E(S1)= k*Q*(1/R²)= (k*Q)/(2r)²= (k*Q)/r² * ¼
= ¼ E(S2)
E(S2)= k*Q*(1/r²)= (k*Q)/r²= (k*Q)/r²= 4 E(S1)
E is inversely proportional to r squared
That proves that with a radius twice smaller, S2 owns an electric field 4 times stronger near it.
If we apply that principle to an infinitely small object, its electric field will be infinitely strong near it. And if we identify a point as a small object, its electric field is strongly worth. It is an important factor that allows the ionization of the air particles wich determines the path of the lightning.
Franklin's Lightning Rod 