90 MICROSCOPIC OBJECTS. 



of view. With few exceptions, these articles are best 

 examined as opaque objects on a black ground, under a 

 magnifying power of from 30 to 60 diameters. In com- 

 mon muslins, linens, silks, and similar fabrics, the threads 

 in both directions are similar, and those in one direction, 

 (say the woof) pass alternately over and under each of 

 those in the other direction (or warp). In ornamental 

 fabrics the two sets of threads not only vary in colour, 

 but often the threads in one direction are twisted more 

 than those in the other ; while a further variation is made, 

 inasmuch as they do not pass alternately over and under 

 those at right angles to them, but pass over two, three; 

 or more threads, and under only one or two. By these 

 means a pattern and a face are given to the goods. The 

 manner in which these numerous and varied effects are 

 produced is readily exhibited by the microscope under the 

 powers before mentioned. The beauty to be met with 

 in these examinations and the pleasure to be derived from 

 them, are greatly heightened by selecting specimens of 

 bright and varied colours, as plaids, checks, and striped 

 goods. — Note. It is well to cut — or, what is better, 

 punch out — a circular piece of the fabric, about half an 

 inch or less in diameter, and mount it upon a black disc 

 or in a wood slide. 



Including nets and lace, there may be collected at least 

 fifty varieties of interesting specimens of this class. 



Inorganic — Aerolites. — ^Thin sections of these stones 

 exhibit a beautiful radial structure. — They require a power 

 of 30 to 80 diameters. 



