He happened on the book in a secondhand bookstore.

他在旧书店里偶然发现了这本书。

I came across these old photos recently.

最近我偶然发现了这些旧照片。

Fleming discovered penicillin by accident in 1928.

弗莱明在1928偶然发现了青霉素。

In 1895, Wilhelm Roentgen accidentally discovered that a cathode-ray tube could make a sheet of paper coated with barium platinocyanide glow, even when the tube and the paper were in separate rooms.

1895，·伦琴偶然发现阴射线管能使涂有亚铂酸盐钡的薄相纸发光，甚至当阴射线管和相纸分别放在不同的房间时也能发光。