114 Prof. Langberg on the influence of Capillary Attraction upon 



consists in loading the instrument with the weight that sinks it 

 (or rather that ought to sink it) in water to the division mark of 

 the scale, at which the unloaded instrument floats in a liquid 

 the specific gravity of which is indicated by that particular mark. 



As I was trying several hydrometers in both these ways, 1 

 was struck by the fact that they never gave altogether consistent 

 results. If, for instance, the instrument tested according to the 

 first method appeared to be accurate, according to Brisson's 

 method it always showed an excess of alcohol in a given mixture. 

 Hydrometers, for example, made at Berlin (even those adjusted 

 at the Royal Prussian Gauge Office) showed from half to one per 

 cent, too little alcohol in comparison with the actual density of 

 the liquid, while the same instruments tested according to Bris- 

 son's method were found almost correct. 



After due consideration, I think the following explanation may 

 be given of the circumstance in question. 



If a cylinder be floated upright in a liquid that wets it com- 

 pletely, the latter, as is well known, rises all round the cylinder 

 against its sides and forms a conical surface, which below spreads 

 out asymptotically to the horizontal surface of the liquid, and 

 above joins the surface of the cylinder with a sharp turn, so that 

 the tangent of the generating curve at the highest point is ver- 

 tical. Now this elevated fluid ring must exert a downward force 

 equal to its weight or hydrostatic pressure, and, if the cylinder 

 float upright, must sink it as much deeper as would be the case 

 if no portion of the liquid were elevated by capillary attraction, 

 but the weight of the cylinder itself were increased by an amount 

 equal to the weight of the liquid raised. 



If a cylindrical disc, a b, be brought into contact with the 



P 9 



surface of a liquid that wets it, and be then slightly raised, 

 the liquid follows it and rises also in the form c abd. Now 

 this elevated liquid column exerts on the disc a downward 

 force, which may be considered as consisting of two parts ; one 

 due to the weight of the cylindrical portion a bop, the other to 

 that of the conical ring a u c, bp d. The first of these is known 



