https://www.scientificamerican.com/article/hydrogen-balloons-could-elevate-telegraph-wires-above-rivers/

“A new method has been proposed for extending the lines of the Magnetic Telegraph across rivers and bays. It is proposed to support the wires in an elevated position, by means of elliptic balloons. These balloons, being each 60 feet in length, will support about 40 pounds each besides its own weight. The cost will not exceed $200 each, being made of thin varnished cloth and inflated with hydrogen gas. A small pipe 1.4 inch in diameter will be extended to each balloon, by means of which the gas in the balloon may be occasionally replenished."

—Scientific American, November 1845