I N C 



HOUR, decimal parts of. See Time. 

 HYDROMETER. See Gravity specific. 



HYDROSTATICALparatfo-r, or bellows. See Fluids, pr eg wre of, 

 HYPERBOLA, principal properties of. See Come Sections, 



ICEBERG. 



According to the experiments of Boyle and Mairan, the volume of gflr- 

 lid compact ice is to that of sea water as 10 to 9 ; therefore the volume 

 of ice which rises above the surface of the water is to that which sinks 

 below it as 1 to 9. Supposing .". a cylinder of ice to rise above the sur- 

 face of the sea 200 feet, which does not exceed the height of some ice 

 islands described by navigators, its depth under water would be 1800 feet, 

 and its whole height 2000 feet. But it is probable that this considerably 

 exceeds the actual height of the Polar Icebergs. For first, the shape of 

 these floating bodies is probably somewhat pyramidal, the part immersed 

 being the broader end. And in the next place, as Mr Wales observes, 

 the ice, which composes these masses, is comparatively light and porous, 

 being chiefly snow and salt water frozen together, and bearing not per- 

 haps a greater proportion to the weight of salt water than that of 5 to 

 6, or 6 to 7 at the utmost. 



Icebergs in both | spheres are sometimes carried by currents as low as 

 40 latitude. 



JETS d'eau.See Fluids, discharge of. 



IMPACT of hard and clastic bodies. See Collision. 



IMPERIAL weights and measures. See Weights. 



INCLINED Plane. 



1. Equilibrium of bodies upon inclined p'anes. 



Let P ^ power, W weight,^ = pressure, H rr height of the plane, 

 B = base, and L = length, , ^ of inclination of the plane, /B = 

 which the direction of the power makes with a perpendicular to the 

 plane, -y = </ which the direction of the power makes with a perpendi- 

 cular to tlw horizon ; then wheu a body is sustained upon the plane, we 

 have the following proportions : 



P : W : : sin. *, : sin. ff. 



Pip:: gin. a. : sin. ^. 

 p : W ; ; sin. y : in, , 



145 I 



