MECHANICS AND USEFUL ARTS. 85 



mercial centres of Europe. In London, the 54 pence sterling, at 

 which a dollar is rated, are really equivalent to 1.095 dollar •" the 

 Frankfort standard, two and one-half silver gulden, to 1.014-i 

 dollar; at Paris, 1.09(34:5 dollar; Antwerp, 1.022G dollar; Bre- 

 men, 1.0989 dollar; Amsterdam, 1.0065 dollar; Berlin, 1.0059 

 dollar; Hamburg, 1.0771 dollar. 



SEA-GOING SHIPS. 



Mr. C. ^Y. Merrifield, F.R.S., at the meetmg of the British 

 Association, read extracts from the re23ort of the committee on 

 the state of knowledge of stability and sea-going qualities of 

 ships. The report treated at considerable length on the rolling 

 of ships in still water, followed by an account of the mechanism 

 of waves and an abridgment of what is known on the subject of 

 the rolling of ships in wave water. The report itself being, in 

 reality, a very condensed abstract of our existing knowledge, it 

 would be difficult to make a useful selection for reading. Mean- 

 while, it may be stated in general terms that the rolling of a ship 

 in still water, and her behavior in a seaway, although interde- 

 pendent, involve very divergent conditions. It seems that the 

 chief point to attend to, to secure ea^y rolling, is that the natural 

 period of the ship's oscillation should not coincide, or nearl}'' co- 

 incide, with the period of the waves ; and there seems reason to 

 suppose that we already know how, in a rough way, to influence 

 the natural periodic time of the ship, so as to be able to predict 

 nearly in what waves she will and in Avhat waves she will nob 

 roll through excessive angles and with excessive quickness. 

 But our knowledge is exceedingly crude and deflcient in detail, 

 and even our known means of obseiTation of the height and form 

 of waves are very unsatisfactory. 



ships' lights. 



M. Tronsens has made a communication to the Paris Academy 

 of Sciences, in which he suggests a new arrangement of ships' 

 lights to prevent collision at sea. He proposes the use of 3 

 lights, arranged in the form of a right-angled triangle, one side 

 of which is vertical, and another parallel, with the medial line of 

 the vessel, and towards the head, and i)lac(?d in the highest pos- 

 sible position. The light of the summit is to be of a different 

 color from the other two, and the distance "between the lights to 

 l^e about 18 feet. Observation of the two lights in a vertical line 

 will, says the author, furnish the ai)proximate distance from the 

 approaching ship, and l)y comparing the apparent distance of 

 tiie two lights on the horizontal side with that of the two on the 

 vertical side, an idea of the ships' route may be obtained ; at any 

 rate the relative distances will show whether that course is to the 

 right or left of the lino of observation, which is the m;iin fact to 

 be ascertained, and that without any instrument. — Meek. Mag.^ 

 July 2, 1809. 



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