202 Baron de la Tour on Metallic Strings^ S^c. 



M. Cagniard de la Tour is of opinion that the preceding re- 

 sult can only be observed in wires formed of substances suffi- 

 ciently solid to support the weight of the atmosphere, which 

 necessarily tends to fill up the vacuities. 



In performing this experiment, our author took a metallic wire 

 two metres (6^ feet long) and about one millimetre (l-25th of an 

 inch) in diameter, and he immersed a portion of it, six milli- 

 metres long, in water which held a glass tube of a very small 

 bore. This portion of the wire displaced the water, and rais- 

 ed it five millimetres in the tube. " Having then" says the Ba- 

 ron, " adjusted this little tube as a thermometric column on a 

 large vertical tube of glass, and sufficiently long to contain two 

 metres of the string, I filled with water the whole apparatus. 

 The inferior end was closed by a cork beyond which the lower 

 end of the cord projected. This end was fixed to a bit of 

 wire driven into a piece of wood which supported the whole, 

 and the lower extremity of the wire was rolled round a cylin- 

 der, by turning which the wire could be stretched at pleasure." 



When the wire was lengthened, so as to be drawn six mil- 

 limetres beyond the small tube, the descent of the column of 

 water, in place of being ^u^ millimetres, as it should have been, 

 had the diminution of its diameter compensated its increase of 

 length, was only from SJ to 2J millimetres. This experiment 

 several times repeated always gave the same result. 



Wishing however to know what would happen if he went 

 beyond the elastic amplitude of the wire, he drew it out six 

 millimetres beyond its primitive elongation ; but in this case 

 the descent of the water in the tube, which ought to have been 

 a little less than in the first experiment, on account of the 

 diminution of the diameter produced by its first extension, 

 was, on the contrary, greater, and approached very nearly to 

 fimr millimetres, because, says the author, «* the wire having 

 been in some degree forced to draw itself like a substance 

 which is ductile but not elastic, there is in this case a greater 

 compensation between its elongation and the diminution of 

 this diameter. 



Baron Cagniard de la Tour proposes to submit to similar 

 trials rods of glass and other elastic substances, but by means 



