The method used by the electricians to discover a fault is one of such delicacy and beauty as shows the marvellous perfection of the instruments which science employs to learn the secrets of nature. The galvanometer is an invention of Professor Thomson, by which "a ray of light reflected from a tiny mirror suspended to a magnet travels along a scale, and indicates the resistance to the passage of the current through the cable by the deflection of the magnet, which is marked by the course of this speck of light. If the light of the mirror travels beyond the index, or out of bounds, an escape of the current is taking place, and what is technically called a fault has occurred." Such was the discovery on Monday morning. At a quarter past three o'clock the electrician on duty saw the light suddenly glide to the end of the scale and vanish. Fortunately it was not a fatal injury. It did not prevent signalling through the cable, and a message was at once sent back to the shore, giving notice of the check that had been received. But the electric current did not flow freely. There was a leak at some point of the line which it would not be prudent to pass over. They were now seventy-three miles from shore, having run out eighty-four miles of cable. The tests of the electricians indicated the fault to be ten or a dozen miles from the stern of the ship. The only safe course was to go back and get this on board, and cut out the defective portion. It was a most ungrateful operation thus to be undoing their own work, but there was no help for it. Such accidents had been anticipated, and before the Great Eastern left England, she had been provided with machinery to be used in case of necessity for picking up the cable. But this proved rather an unwieldy affair. It was at the bow, and as the paying-out machine was at the stern, the ship had to be got round, and the cable, which must first be cut, had to be transferred from one end to the other. This was not an easy matter. The Great Eastern was an eighth of a mile long, and to carry the cable along her sides for this distance, and over her high wheel-houses, was an operation at once tedious and difficult.