30 THE AMERICAN MONTHLY [Jan., 



been most fruitful in developing interesting and valuable knowl- 

 edge of a scientific and truly i)ractical character. An examina- 

 tion of a section by means of the microscope will sliow not 

 merely the various substances which compose it, but also the 

 method according to which they are arranged, and by which 

 they are attached to one another. For example, pyrites is con- 

 sidered to be the enemy of the quarryman and constructor, 

 since it decomposes with ease and stains and discolors the rock. 

 Pyrites in shar}), well-defined crystals sometimes decomposes 

 with great difficulty. If a crystal or grain of pyrites is embed- 

 ded in soft, porous, light-colored sandstones, its presence will 

 certainly demonstrate itself by the black spot which will form 

 about it in the porous stone, and will permanently disfigure an<l 

 mar its beauty. If the same grain of pyrites is situated in or 

 near very hard, comi)act, non-absorbent stone, the constituent 

 minerals of which are not rifted or cracked, this grain of pyrites 

 may decompose and the products be washed away, leaving the 

 stone untarnished. 



MICROSCOPICAL APPARATUS. 



Indestructible Clay Wick. — A lamp wick made entirely of 

 clay giving 25 per cent more light than cotton wick ; made cap- 

 illary by incorporating with the clay while in a plastic state, 

 filaments of unspun vegetable fibre which are burned out in the 

 process of baking the clay. 



The object is to provide an indestructible wick which shall 

 possess all the advantageous qualities of an ordinary cotton or 

 fibre wick; but which shall in addition last an indefinite time 

 without renewal or necessit}' of trimming or care. 



When the clay is baked the vegetable fibre is burned out, 

 leaving capillary tubes running longitudinally through the wick 

 through which the oil from tha lamp will be raised to the flame 

 by capillary attraction. Owing to the perfect combustion of the 

 wick, the flame is ])erfectly white in character, devoid of odor 

 and smokeless. It is found through a practical test, that the 

 oil is volatilized by the Ui-e of this wick and the vapor is con- 

 sumed tlius giving the above results. 



Unspun vegetable fibre, owing to its fineness of thread is 

 superior to all other filaments, the manufactured being too 



