The unlocking of screws, where _washers_ had been introduced as a security, was rather unexpected, and the writer took an opportunity of conversing with his much respected friend Professor PLAYFAIR of Edinburgh, regarding this circumstance. The Professor observed, that he had experienced some inconveniency of this kind from the unlocking of almost all the screws of a telescope, which had been sent to him from London by the mail-coach. Indeed from the spiral form of the screw, which is, in fact, an inclined plane, Mr Playfair readily accounted for such an occurrence; and when reflected upon, it seems to be an effect rather to be looked for, and is a reason why rivetting the point of a bolt, in preference to screwing it, should generally be resorted to, where much friction or motion is to be apprehended. [Sidenote: 1807, December.] [Sidenote: State of the Floating-light.] At this visit to the Bell Rock, the writer went also on board of the Floating-light, where every thing was found in good order. On some occasions Mr Sinclair, the commander, stated, that the vessel had rolled excessively hard; that she had shipped two or three very heavy seas over the waste-boards, and that he had found it occasionally necessary to veer out 80 fathoms of cable. He also stated, that the floating-light had been _run foul of_ by a large smack-rigged vessel, with all her canvas set, though the lights were burning perfectly clear. This vessel had struck upon the larboard quarter, damaged the taff-rail, and started three of the floating-lights’ trenails. That they immediately hailed the vessel, but she sheered-off, and her crew made no reply. The smack was beating to the northward, and was much lumbered on the quarter-deck with packages of earthen-ware, which were distinctly seen upon her deck from the brilliancy of the lights. The sailors on board of the floating-light were all in good health, and appeared to be satisfied with their situation. The master, however, mentioned, that his crew, particularly the young men, calculated very sharply about their turns for leave on shore, which came round in the course of about six weeks. Indeed, the probability is, that had the seamen not been rather compelled to this duty, as a protection against the Impress-service, it might have been found extremely difficult to get able seamen to undertake so dreary a life as the continual round of riding at anchor in the open sea, without the company of other shipping, or the pleasure of intercourse with the shore, as is the case in the ordinary road or anchorage for shipping.