Oil. A TREATISE ON PILF,. 



where it is about eight inches. To ihe latter, as a general rule, it may be observed that 

 the smallest square, magnitude visible to the naked eye, either of white particles upon a 

 black ground, or of black particles upon a white ground, is 4 ,', . of an inch, but when the 

 substance is in lines instead of particles, it may be seen, if held towards the light, when 

 only ^TjVo of an inch in diameter. The finest wool that we have examined, corning from 

 the body of a sheep, is o-iVo P ar t of an inch, which, according to the above rule, can be 

 seen with the naked eye. There is a point beyond which an object cannot be seen ; 

 owing, perhaps, to the light being absorbed before it reaches the retina. This point, (which 

 is called the " vanishing point,") must, of course, depend upon the eye, the light, the color 

 and the size of the object ; where the light, the color and the size of two or more objects, are 

 alike the distance of the vanishing point, to the same eye, must always be identical. Now we 

 propose that a series of tubes, to draw out one from another, like those of a telescope, be con- 

 structed of sufficient length that, when fully drawn, they are equal to the vanishing point of 

 the coarsest wool desired to be examined. Upon a piece of card arrange a series of strands of 

 wool, in the order of fineness, the diameters of which have been previously ascertained with 

 the microscope and micrometer. Upon a similar card stretch a strand of the wool, the relative 

 diameter of which it is required to ascertain, and, upon fixing it near one end of the tube, 

 (one eye to the other end,) draw out till you find the vanishing point of the strand. Re- 

 move this card and put the other one in its place, when it will be perceived which of the 

 filaments upon it is at its vanishing point, and the diameter of that strand will be the one 

 required. The tubes may be made of tin or even of pasteboard, but ought to be blackened 

 in.-ide. The measured wool upon the cards can be procured in this city for a triile. 



OF HYPERTROPHY OR UNNATURAL GROWTH OF HATR. When hair grows to such an 

 unnatural length as to cause disease, it is called "hypertrophy."* Dr. Gross tells of a 

 young lady who died of this disease She had always experienced an unusual growth of 

 hair, and generally kept it cut short; but, a few months before her death, it grew down to 

 her heels. It was flaxen and had a soft oily feeling. The account concludes with the 

 remark that a post-mortem examination showed that the unnatural growth of hair had 

 caused her death. f 



OF DEPILATION. Some Malays destroy the hair with quick-lime, the isolated ones 

 being plucked out with tweezers. (Latham, Nat. Hist, of Var. of Men, 148.) Most 

 American Indian tribes pluck out their beards. 



OF THE DISCOTOME. Description of a very convenient instrument for cut ting transverse 

 sections or disks of hair, which we call a Discotome.f 



h 



* From hyper uper, or above, and trix, hair. 



t The corrosive medicines used to take a\vnv superfluous hair are called " Ertillolirn;" from "ek," out, and "tillo," to 

 pluck. 



j From discos, a disk, and temno, to cut. 



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