563 



cles. The more highly a bar is magnetized, the more it becomes 

 susceptible of a loss of power by agitation. 



" An Account of a Protracting Pocket Sextant." By Colonel 

 Bainbridge. Communicated by P. M. Roget, M.D,, Sec. R.S. 



The object of the invention here described is to facilitate and ex- 

 pedite the making of sketches and surveys for military purposes on 

 actual service, and by serving at once as a sextant and protractor, so 

 that as soon as an angle is taken, it may at once be laid down on 

 paper by employing the two legs of the instrument as rulers. A de- 

 scription referring to a diagram is given of this portable sextant. 



" Observations on the Growth and Development of the Epider- 

 mis." By Erasmus Wilson, Esq., F.R.S., Lecturer on Anatomy and 

 Physiology in the Middlesex Hospital. 



The author adduces evidence derived from his microscopic obser- 

 vations, in confirmation of the commonly received doctrine respect- 

 ing the origin of the cells of the epidermis and epithelium generally, 

 from the materials furnished by the liquor sanguinis or plasma of 

 the blood ; which fluid, passing by endosmosis through the walls of 

 the- capillary vessels and peripheral boundary of the surface, deve- 

 lopes granules by a vital process, analogous to coagulation. On a 

 careful examination of the inner surface of the epidermis with the 

 aid of the microscope, he finds it to be composed of four kinds of 

 elements, arranged in such a manner as to constitute an irregular 

 plane, similar to a tesselated or mosaic pavement. These elements 

 are, — 1. Granules, which the author terms primitive, of a globular 

 form, solid and apparently homogeneous, and measuring about , 

 1 -20,000th part of an inch in diameter. 2. Aggregated granules, 

 having about double the diameter of the former and apparently com - 

 posed of as many of these as can be aggregated together without 

 leaving an unoccupied space in the centre of the mass. 3. Nucleated 

 granvJes measuring in diameter from the 6000th to the 4000th part 

 of an inch, each being composed of an aggregated granule as a 

 nucleus, enveloped by a single layer of aggregated granules, giving 

 to the whole mass an oval or circular, and at the same time flat- 

 tened shape. Their constituent granules have acquired, during this 

 aggregation, greater density, and are separated from each other by 

 distinct interstitial spaces filled with a transparent homogeneous sub- 

 stance. 4. Nucleolo-nucleolated cells pervading the deep stratum of 

 the epidermis, and of which the longer diameter measures from the 

 3000th to the 2500th part of an inch. These cells, which constitute 

 the principal portion, and may be regarded as the chief constituent 

 of the epidermis, are formed from the nucleolated granules, on the ex- 

 terior of which there is superposed a transparent layer, bounded by a 

 well-defined outline, by the dark interstitial substance of the wall of the 

 cell ; the nucleolated granule being the nucleus, and the aggregated 

 granule the nucleolus of these primitive cells of the epidermis. The 

 author is of opinion that the nuclei, up to a certain point, grow with 

 the cells, by the separation of the original granules from the deposi- 



