In the course of time my friends arrived on the opposite bank (скоро мои приятели пришли на противоположный берег; in the course of time — с течением времени), and they stopped and watched him too (остановились и тоже /стали/ наблюдать за ним). His back was towards them, and they only saw his jacket and cap (его спина была /повернута/ к ним = он стоял к ним спиной, и они видели лишь его куртку и кепку). From this they immediately jumped to the conclusion that it was I, their beloved companion (на основании этого/поэтому они сейчас же сделали вывод, что это я, их любимый товарищ; to jump — прыгать; поспешно, необдуманно приходить к /заключению, выводу и т. п./), who was making an exhibition of himself, and their delight knew no bounds (выставляющий себя на посмешище, и их радость не знала границ; exhibition — выставка, показ; delight — удовольствие, восхищение, наслаждение). They commenced to chaff him unmercifully (они начали дразнить его немилосердно; to chaff — рубить, резать /сено, солому/; подшучивать, дразнить, смеяться).

conclusion [kn'klu:n] exhibition [,eks'bn]

The people about the river began to get quite absorbed in him after a while, and to make bets with one another as to what would be the outcome of his next push.

In the course of time my friends arrived on the opposite bank, and they stopped and watched him too. His back was towards them, and they only saw his jacket and cap. From this they immediately jumped to the conclusion that it was I, their beloved companion, who was making an exhibition of himself, and their delight knew no bounds. They commenced to chaff him unmercifully.

I did not grasp their mistake at first, and I thought (я сначала не понял их ошибку и подумал), "How rude of them to go on like that, with a perfect stranger, too (как невежливо с их стороны так вести себя, да еще с совершенно незнакомым человеком)!" But before I could call out and reprove them (но прежде, чем я смог крикнуть и упрекнуть их /в этом/), the explanation of the matter occurred to me, and I withdrew behind a tree (объяснение дела пришло мне в голову = я понял, в чем дело, и спрятался за деревом; to withdraw — отдергивать /руку/; брать назад; удаляться).