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by weighmg a veEsel of kncwn volume, first exhausted using about 100 feet, and introduce it in shunt with a nm, thep full of air the difference of weights represent-resistance in the other branch of one-tenth ohm. This ing the weight of air contained. you can !ret from a piece of lamp carbon, uncoated, ],2 inch diameter and 12 inches long. Your best plan is to put in a longer piece of carbon wIth a sliding contact, connect your cOli, and slide the contact along until proper power isJ attained.doi:10.1038/scientificamerican10051889-219a fatcat:q7nivxjopne7bhutiiuuvz32cq