_Monday, July 24th._--The morning was exceedingly fine, and the ship proceeded steadily at an average rate of 6 knots an hour, with a light favouring wind and a calm sea. Those who were up betimes had just taken a turn or two on deck, watching for the early dawn, when they observed some commotion in the neighbourhood of the Testing-Room, and soon afterwards the ship’s engines were slowed and stopped. According to Professor Thomson’s galvanometer, which is used in the system employed in testing, 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 along 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 in the Cable, and what is technically called a fault has occurred. At 3·15 a.m., when 84 miles of Cable had been paid out, the electrician on duty saw the light suddenly glide to the end of the scale, and then vanish. The whole staff were at once aroused--the news soon flew through the ship. After testing the Cable for some time by signalling to and from the shore, Mr. de Sauty satisfied himself that the fault which had occurred was of a serious character, and measures were taken accordingly to rig up the picking-up apparatus at the bow, to take in the Cable till the defective portion was reached and cut out. Such an early interruption to our progress caused a little chagrin, but the veterans of submarine telegraphy thought nothing of it. Whilst the electricians were testing, to obtain data respecting the locality of the fault, the fires were got up in the boilers of two small engines on deck to work the picking-up machinery. At 4 a.m. a gun was fired by the Great Eastern to call the attention of the Terrible and Sphinx to our proceedings, and they were also informed by signal of the injury. Notwithstanding the skill and experience of the scientific gentlemen on board, there was a great vagueness of opinion among them respecting the place where the fault lay. Some believed the defective part was near the shore, and probably at the splice of the shore end with the main Cable; others thought it was eastward or westward of the same place; and calculations, varied by uncertain indications given by the currents showing that the fault itself was of a variable character, and permitted the currents of electricity to escape irregularly, were made by the scientific staff, which fixed it at points from 22 to 42 miles--one at 60 miles--from the ship. But repeated observations gave closer results. Mr. Varley came to the conclusion that the fault was not very far from the ship; and Mr. Sanders, a gentleman who had much experience in fault-finding, arrived at the conviction that it was not more than 9 or 10 miles astern.