قصة الكتاب :
\r\nBook Excerpt: ... used to the climate for a long time in order not to fear any harm from tropical rain; so we stayed on the bank to watch the electrometer. I held it in my hand 6 feet above the ground for 20 minutes and saw the lilac marrow globules, usually only a few seconds before the lightning strike, diverging four lines. The electrical charge remained the same for several minutes; We had time to investigate the nature of electricity by means of a sealing wax stick, and so I saw here, as often later on the ridge of the Andes during a thunderstorm, that air electricity was first positive, then zero and finally negative. This change between positive and negative (between glass and resin electricity) was repeated several times. Meanwhile, a little before the flash, the electrometer showed only zero or positive electricity, never negative