Chemical Science. 415 



haps before drawn, that it is not produced in the iron, but 

 given to it by the external magnetism of the earth ; all that the 

 motion given to the iron in the various mechanical processes 

 used, does, is 1o render it more susceptible of receiving magnet- 

 ism. One of his modes of giving this motion to the particles, 

 is to fix one end of a rod of iron or steel steadily, placing the 

 rod in any position required, as either perpendicular or parallel 

 to the dip, &c., and then to make it vibrate by drawing the 

 free end from the axis of the rod, and suddenly letting it loose. 

 If in a favourable position, the iron soon acquires magnetism. 



3. Effect of Iron on the rate of Chronometers. — Mr. Barlow, 

 of Woolwich, has lately made experiments on the effect of 

 iron, free from any permanent magnetism, in altering the rates 

 of chronometers placed in its vicinity. Mr. Fisher had remarked 

 the dift'erence of rate occurring in his chronometer when on 

 board and on shore, though the vessel was frozen in, and there- 

 fore could produce no variation by its motion. He therefore 

 attributed it to the magnetic action of the iron in the vessel, a 

 conclusion that has been confirmed by Mr. Barlow's experiments. 



In these experiments, various chronometers were placed in 

 different positions near amass of unmagnetic iron, and an alte- 

 ration in the rates of them observed. This alteration varied with 

 their respective situations to the iron, but was always uniform 

 in the same position. The effects amounted sometimes to 5'per 

 day, and were at last traced to magnetism in the balance and 

 spring of the chronometer. 



The plan suggested by Mr. Barlow, of estimating the effects 

 of a ship's metal on the compass needle, namely, by placing a 

 plate of iron in such a position, and so near to the needle, as to 

 be equal in effect to the rest of the metal in the ship, is well 

 known, and the return of his Majesty's ship Leven, from a 

 voyage of sixteen months, affords proof, by the experiments 

 that have been made on board, of its value. The same plan is 

 now proposed by him for ascertaining the ship-rates of chrono- 

 meters before they go on board, by simply taking their rates on 

 a certain situation, and at a proper distance, from such a plate 

 of iron. 



4, Electro- Matjuc tic Rotation. — An ingenious little instrument 

 has been invented by M. Ampere, in illustration of the rotatory 

 motion of the wire round the pole of a magnet. Its advantage 

 consists in comprising the vol laic combination used in itself. 

 Suppose a cylinder of co[)per, about two inches in diameter and 

 tiie same in height, and within it a smaller cylinder about half 

 an inch in diameter; these are fastened together by a bottom, 

 having a hole in its centre the size of the smaller cylinder, so 



