How many electrons are there in $1 \ C$ of charge?

The minimum charge on an object is

By which instrument can the charge on an object be detected?

In a Millikan's oil drop experiment,the charge on an oil drop is calculated to be $6.35 \times 10^{-19} \ C$. The number of excess electrons on the drop is:

While doing his experiment,Millikan one day observed the following charges on a single drop:
$(i)$ $6.563 \times 10^{-19} \ C$
$(ii)$ $8.204 \times 10^{-19} \ C$
$(iii)$ $11.50 \times 10^{-19} \ C$
$(iv)$ $13.13 \times 10^{-19} \ C$
$(v)$ $16.48 \times 10^{-19} \ C$
$(vi)$ $18.09 \times 10^{-19} \ C$
From this data,the value of the elementary charge $(e)$ was found to be:

What was found by Thales of Miletus?