Desmptioti of a new Reflecting Compass, 7 



the centre of the egg. These shells are wholly extra- vascular, 

 and their albuminous membranes are alike cuticular, whilst the 

 inner true memhrana putaminis is made reticular and capable of 

 vascular organization. The order of deposit in these examples 

 is like that of enamel in teeth, which appears to be precipitated 

 upon the Ijone of the tooth under the guidance of a mem- 

 branous case or mould. From a disordered fowl, I have seen 

 eggs produced the calcareous crusts of which were inflated with 

 bubbles, so as to form a cancellated shell in texture like pumice- 

 stone. The most durable substances of animal bodies, such as 

 the bones and teeth, are only partly vascular, since their calcareous 

 materials are fixed by chemical precipitants, and remain under 

 chemical laws. Injuries done to the horns of cattle, to the hoofs 

 of animals, and to human nails, are never restored ; those parts 

 do not possess the power of self-repair, and it is only by me- 

 chanical wearing away that such injuries are obliterated. In- 

 deed, the beneficent construction of animal nature is sufficiently 

 manifested in the insensibility of all the exuvial coverings, and 

 in the inorganic composition of many parts which are exposed 

 to mechanical attrition ; as the enamel of teeth, the horny beaks 

 of birds, and the cuticular or horny coverings of feet. The same 

 beneficence appears to be extended to many parts of the ex- 

 ternal organic substances by which painful sensations are ob- 

 viated; while the substances themselves, being left directly under 

 the dominion of the vital superintendancy, become more perma- 

 nent : — such parts are the tendons ligaments, cartilages, cellular 

 tissue, the gelatine and lime of bones. Even water is an essen- 

 tial constituent of the animal fluids, and affords the necessary 

 softness and flexibility to the solids. — But this subject and its 

 connexion with the vegetable composition and texture extends 

 far beyond the limits of a memoir, and I must therefore suspend 

 my observations. 



[To be continued.] 



II. Description of a v.ew Reflecting Compass. By Mr. 

 T. Jones, 02, Charing Cross, London. 



Among the various instruments used for siuveying, the com- 

 pass appears to have been least considered ; and this has pro- 

 bably arisen from its want of portability when fnrnished with a 

 stand, and the conviction that under the most favourable circum- 

 stances it is far inferior to the theodolite ; and yet requires 

 equal care in its adjustment and use. 



But in military sketching, in the delineation of roads, rivers, 

 &c. and in all surveys where rapidity is more an object than ex- 

 treme accuracy, the compass will be found a most valuable aux- 

 A 4 iliary, 



