"XVI. Summa serei infinita harmonicè progressionalium, &c. est infinita. Id primus deprehendit Frater:…"
[16. The sum of an infinite series of harmonic progression, , is infinite. My brother first discovered this…]
Bernoulli, Johann (1742). "Corollary III of De seriebus varia". Opera Omnia. Lausanne & Basel: Marc-Michel Bousquet & Co. vol. 4, p. 8.
Johann Bernoulli's proof is also by contradiction. It uses a telescopic sum to represent each term as
Changing the order of summation in the corresponding double series gives, in modern notation
.