MICROSCOPIC INSTRUMENTS. 353 



Avhich is placed within the tube and is moveable by a milled 

 head on the outside ; the upper portion of the tube supports 

 the optical part which is made to fit within a short tube, in 

 which it may be easily moved with nicety and steadiness, 

 for bringing the object into the focus of the glasses. This 

 instrument, though of low price, is constructed as the best, 

 having three lenses in the compound body, the eye-glass 

 being the one nearest the eye, the object-glass the nearest 

 the object viewed, and a larger lens than either of these 

 intermediate between them, called the field or amplifying 

 glass. In the lower-priced instruments but one object- 

 glass accompany them, having a power of about forty 

 diameters, or 1,600 times; those with two object-glasses 

 magnify nearly twice as much, and with three, about 100 

 diameters, or 10,000 times. The size of this instrument 

 is one third larger than the cut. A test-object, several 

 glasses for laying objects on, and a pair of tweezers, 

 accompany the instrument ; the whole packed in a neat 

 mahogany box. Price, ordinary quality, $'3.00. 



" best quality, $3.50. 



Larger size, one half larger than cut, with one addition- 

 al object-glass. Price $5.00. 



Largest size, twice the size of the cut, 11 inches long, 

 body tube 2 inches diameter, with three object-glasses, 

 condensing lens for illuminating opaque objects, and addi- 

 tional test-object and glasses. Price $9.00. 



Achromatic Microscopes. " The rapid advances which 

 have been made in modern times toward a correct knowl- 

 edge of the intimate structure of animate and inanimate 

 bodies, by the employment of the microscope, have given 

 to this instrument an importance second only to that of 

 the telescope. By its agency alone, have crude notions 

 and theories been swept away, and science in civilized 

 countries made to stand on a firmer basis. In this land 

 of machinery and manufactures, artists have not been 

 found wanting to devote their time and talents to the con- 

 version to what might once have been an amusing instru- 

 ment or a toy, into one of the most powerful auxiliaries 

 that can be employed in scientific research. In propor- 

 tion to its use, such has been the demand for improvement 

 in its construction, that both amateur and optician have 

 labored together to bring it to its present state of perfec- 

 tion." 30* 



