94 MICROSCOPIC ILLUSTRATIONS. 



here selected can be inclosed in a case no larger than is 

 necessary to contain all the other parts of the micro- 

 scope m 3 and, with a given weight and dimensions, the 

 form is more steady than when the feet are of equal 

 length. Of course, to obtain the greatest advantage, the 

 stem, c, should always be over the shortest foot. 



Having alluded to the packing of microscopes, it may 

 be mentioned, that upright cases or cabinets are greatly 

 superior to boxes for the purpose, because, the instant 

 the door is unlocked, the instrument is ready for use ; 

 besides, sufficient space is afforded for a nest of drawers, 

 to contain the apparatus and objects, although the latter, 

 perhaps, are better kept in a separate cabinet. 



On the selection of proper Magnifying Powers. — In a 

 microscope constructed for single lenses, doublets, or 

 triplets, the plain split end of the arm, a, is the situation 

 designed to receive them. Upon examining the lenses, 

 such as possess the largest aperture are of the lowest 

 power. With these our observations should generally 

 begin. There should be marked, on them all, their 

 respective sidereal focal lengths. This measure will 

 indicate very nearly the distance at which they require 

 to be adjusted from the object. When the object to be 

 examined is a seed or large body, commence with either 

 of the three lowest powers. If the object is hardly 

 perceptible with the naked eye, take those of 1-1 Oth of 

 an inch focus, and so proceed, step by step, to the higher 

 powers. 



