218 



Experimental Inquiries relative to the Distribution and Changes of the 

 Magnetic Intensity in Ships of War. By George Harvey, Esq. 

 Communicated by John Barrow, Esq. F.R.S. Read Feb. 26, 1824. 

 [Phil. Trans. 1824,^.310.] 



This paper contains the details of experiments made on board se- 

 veral vessels, with a view of determining the influence of the iron in 

 the ships upon the compass under different circumstances and situ- 

 ations. The instrument used for determining the intensity con- 

 sisted of a magnetized cylindrical bar, 2' 5 inches long and three 

 eightieths of an inch diameter, delicately suspended by a single fibre 

 of the silkworm, to the extremity of an adjusting screw, which 

 worked in the cap of the glass vessel inclosing the bar. A brass wire 

 also passed through the cap for the purpose of placing the bar at 

 right angles to the magnetic meridian previous to its being put into 

 a state of oscillation. 



On the days devoted to the experiments on ship-board, the time 

 of making 50 vibrations of the bar was determined in the centre of a 

 meadow, of which the substratum was dry slate, by a mean of six 

 sets of experiments, the time being accurately registered to quarter 

 seconds. The instrument was then taken on board, and placed in 

 succession at the different stations of the ship, and the mean of six 

 sets of experiments determined at each station with the same pre- 

 cautions as on land. The times, says the author, of performing the 

 oscillations on shore, and at each of the assumed points in the ship, 

 necessarily gave the magnetic intensity at each station in terms of the 

 terrestrial intensity, which in this case was represented by 100. 



Experiments on the Elasticity and Strength of Hard and Soft Steel. 

 In a Letter to Thomas Young, M.D. For. Sec. R.S. By Mr. 

 Thomas Tredgold, Civil Engineer. Read March 25, 1824. [Phil. 

 Trans. 1824,^.354.] 



The bars of steel used in these experiments were supported at the 

 ends by two blocks of cast iron, resting upon a wooden frame, and a 

 scale for weights was suspended from the middle of the length of the 

 bar, by a cylindrical steel pin, three eighths of an inch in diameter. 

 To measure the flexure a quadrantal piece of mahogany was at- 

 tached to the frame, with a vertical bar sliding in two guides at its 

 edge, and moving an index. The bar and index were so balanced, 

 that one end of the bar bore with constant pressure upon the speci- 

 men, and the graduated arc was divided into inches, tenths, and 

 hundredths. The thousandths were measured by a vernier. A bar 

 of blistered steel of file hardness, 13 inches long between the sup- 

 ports, underwent no permanent alteration of form when loaded with 

 1 lOlbs. The temper of the bar was then successively lowered, and 

 it was ultimately again hardened ; but in these different states its 

 flexure and resistance to permanent change of form remained the same. 



