Within a few years several methods had been proposed by different inventors, but none was at first very successful, not from any fault in the principle, but because the effect of electrostatic capacity of the line was left out of account in the early arrangements.
Utilizing this principle many inventors have devised forms of electrostatic voltmeter.
Certain other inventors have applied the same principle in a different way.
More modern inventors have therefore adopted the plan of drawing the glass direct from the furnace.
If the arguments chiefly relied on for an early date are so precarious or can even be turned against their inventors, there are others of an unambiguous kind which make for a date in the Persian period.