MICROSCOPIC OBJECTS. 97 



lar or egg shape. Their colour is a pure white, and their 

 surface so exquisitely polished, that a minute image of a 

 candle reflected fi'om their surface may be seen in the 

 microscope. — Magnifying power 35 to 80 diameters. 



The sand of the Arabian desert on minute examination 

 is found to consist of small globular bodies of carbonate 

 of lime similar to those grains which compose oolites. 

 It is probable that the spherical form is given to them by 

 abrasion against each other, caused by the winds ; and 

 should at any future period water charged with lime pass 

 over them, they may be converted into stone. 



Sand from Turkey Sponge. — Under this name may be 

 found a variety of minute fossils, some entire, others 

 mere fragments. Among the most interesting are the 

 Foraminifera, which resemble in miniature the chambered 

 shells of the nautili, portions of small corallines, and 

 other zoophytes. — A magnifying power of 80 diameters 

 is sufficient. 



Sarde. — The sihceous stone called by the ancients 

 Sarda is found on the shores of the Red Sea. It is 

 very hard, and is much valued by jewellers for seal- 

 stones and ring-stones. Some valuable antique engrav- 

 ings are on Sarde. When cut into plates about -o^^th 

 of an inch thick, polished, and mounted upon a plate of 

 glass, they form interesting objects for the microscope. 

 In the light- coloured parts is sometimes seen a small 

 spiral scroll-hke form, with radiating striae of c^cedony 

 around it. 



Water, Decomposition of. — ^This phenomenon is admi- 



