3B6 Ohservati&ns on the Structure of Human Hair, 



tion is elliptical or oval. The flattened form appears to be ne- 

 cessary to the curling of the hairs, and the cylindrical figure 

 seems to form an obstacle to it. In Negroes, the hairs present 

 a very marked flattening. In the wool of the sheep, which ap- 

 pears to be cylindrical, another cause probably gives rise to the 

 phenomenon of curling ; namely, the transverse inequalities with 

 which the surface of the hairs is furrowed. 



The author gives four tables of micrometrical measurements 

 of the hairs of the white man and Negro. In the numerous ob- 

 servations which he made, he sometimes found these parts ul- 

 cerated, as it were, at their surface, like carious teeth. The 

 hairs of the back of the hand frequently break at some distance 

 from their point. This rupture appears to be a normal pheno- 

 menon, which nature employs to prevent these hairs from be- 

 coming elongated beyond measure. At the place of rupture, 

 there are observed small interlaced fibrils, which for some time 

 retain, in contact, the two ends placed together at a right angle, 

 until their detached extremity at length falls. 



The author has also made some experiments on the" elasticity 

 of the human hair. It may be elongated about a third of its 

 length. The contraction which follows is somewhat less ; the 

 hair of the roe has scarcely any extensibility, and breaks with 

 the greatest ease. It has more analogy to the feather of a bird 

 than to human hair. 



On the Level of the Sea. 



It is well known that the ocean retains the same level in the 

 deep basins of the sea, and that its vast surface preserves a 

 permanent form all around the globe. If it be raised by tem- 

 pests it is reduced by equilibrium within the limits which are 

 assigned to it. If the earth, as Pouillet remarks *, were im- 

 moveable, and formed of homogeneous strata, the surface of the 

 sea would be strictly spherical. The navigators who pass under 

 the line, those who traverse unknown seas in either hemisphere, 

 and those who visit the coasts of Greenland, or the seas still nearer 



• Pouillet's Elemens (k Physique, t. i. p. 137. 



