Mechanical Science. 223 



4. Experiments on the Resistance of various Bodies to rupture, 

 caused by Longitudinal Tension, by M. Navier. — According to 

 these experiments, iron has not its tenacity increased when la- 

 minated, as ha])pens when it is drawn into wire. Six experiments 

 on iron-])late, with the power applied in the direction of the length 

 of the sheets, indicated a mean force of 41 kilogrammes for each 

 square millemetre* of the transverse section. Four experiments 

 on iron-plate, drawn perpendicularly to the length of the sheets, 

 indicated a force of 36 kilogrammes. 



Two experiments on sheet-copper indicated a force of 21 kilo- 

 grammes for each square millemetre. 



Six experiments on laminated lead indicated a force of 1.33 

 kilogrammes for each square millemetre. It may be concluded, 

 that the lead resists less for equal sectional surfaces, as it is rendered 

 thinner. 



Seven experiments on tubes and rods of glass indicated a force 

 of 2 1 kilogrammes per square millemetre. 



Generally the iron began to lengthen sensibly, and to alter, with 

 charges equal to about two-thirds, at least, of that required to effect 

 the rupture. The same effect happened with copper, charged with 

 a weight equal to half that required to occasion rupture. With 

 lead, the effect was produced by rather less than half the final charge. 

 These three substances presented very different appearances during 

 and after rupture. The lengthening of the iron before it broke was 

 irregular, and varied from l-2()th to 1-lOth of the original length. 

 The copper lengthened about 2-5ths of its first length before it 

 broke, its other dimensions diminishing in consequence. The lead 

 increased by about 1-lOth of its original length, with a force a little 

 less than sufficient to break it ; but with a slightly-increased charge 

 it gradually and progressively diminished in breadth and width, and 

 when separated, the two parts presented a kind of cutting edge, by 

 the gradual diminution of thickness, whereas the other substances 



broke suddenly with a transverse fracture. Annates de Chimie, 



xxxiii. 225. 



5. Magnetism of Watch Works corrected. — It is an important 

 matter with watch and chronometer makers to neutralize concen- 

 trated magnetism, in the most minute parts of the steel works of 

 time-keepers, as chronometers, &c. without the aid of heat. The 

 endeavour to perform this is usually made by touching the part mag- 

 netised with the similar pole of a small magnet; but so unsuccessful 

 is the operation generally, that it is avoided as often as possible. 

 Mr. Abraham was induced, by the consideration that " time-pieces 

 generally become actively magnetical, without being brought into 

 contact with the agent that concentrates the fluid," to conceive that 

 the magnetism developed might be dissipated in a similar way, and 



* A miliemetiejs 0*03937 inches; a kilogramme is 15406 grains. 



