368 THE SCIENTIFIC PAPERS OF 



through the medium of a strong and short horseshoe spring, the 

 object of which is to soften the contact between the two points, 

 and thus allow of the natural oscillations of the weighty column 

 as influenced by the motion of the vessel. The pitch of the 

 micrometer-screw being 5 millims. nearly, and the graduated 

 circle being divided into 1000 equal parts, it follows that each 

 division of the scale through which the screw is turned raises the 

 contact-point '005 millim., a quantity which is intended to 

 represent the depth of a fathom. The micrometer-screw is turned 

 by a wheel geared into a pinion, which is brought up to a place 

 near the point of suspension of the instrument, where it can be 

 turned by means of a milled-head, without the observer being in- 

 convenienced by the oscillations of the instrument relatively to 

 the vessel. Instead of two spiral springs three might be applied, 

 dividing the circle equally, probably with some advantage, viz. 

 that of imparting additional steadiness to the crosshead in its 

 horizontal position. The letters of reference on the drawing, with 

 the references given below, sufficiently describe the mechanical 

 details of the instrument. It remains to be shown how an instru- 

 ment answering to this description can be depended upon for 

 giving true indications of the varying depths of water below the 

 same, notwithstanding changes of temperature, of atmospheric 

 pressure, and of geological formation and condition of the bottom 

 of the sea. 



INFLUENCE OF TEMPERATURE. In considering the influence 

 of temperature upon the instrument, it was necessary to investi- 

 gate its action upon the component parts separately. The effect 

 of temperature upon the linear dimensions of mild steel, of which 

 the instrument is mainly composed, is sufficiently well known. 

 Steel expands, according to the experiments of Dulong and Petit, 

 000012 of its length for every degree Cent, rise of temperature 

 between and 100 C. ; and this number agrees closely with 

 experiments by Regnault, who found the cubic expansion of 

 mercury to be '00018153 per degree C., between and 100 C. ; 

 in both these metals the ratio of expansion by heat may be 

 considered as strictly arithmetical between ordinary limits of 

 temperature. 



INFLUENCE OF TEMPERATURE ON STEEL SPRINGS. Regarding 

 the influence of temperature upon the elasticity of springs, we 



