Microscope Construction, Use, and Core 201 



period of a microscope is approximately 20 years. Replacement of 

 the ocular and high-power objectives after 15 years is a good invest- 

 ment which may extend the life of the microscope for another 15 

 years. Periodic mechanical overhauling and refinishing of metal parts 

 should be done by a competent fine-instrument mechanic. Major 

 repairs and lens work should be entrusted only to the manufacturer. 

 Considering the first investment, the low cost of upkeep, the large 

 trade-in allowances, and the many generations of students served 

 during a normal life span of a microscope, this instrument is the 

 least expensive item of laboratory equipment. 



The foregoing brief discussion of the principal types of micro- 

 scopes and of the essential optical and mechanical features can be 

 supplemented by a study of the well-illustrated descriptive catalogues 

 of the leading manufacturers. Details of construction of specific models 

 are available in leaflets provided by the manufacturers. 



The belief in the superiority of the continental European optics 

 may have been well founded 50 years ago, but is no longer a prime 

 factor in purchasing an instrument. A choice among the better-known 

 makes is now largely a matter of personal preference. The prospective 

 purchaser should examine and, if possible, use various models and 

 base his preference on mechanical and optical features and specifica- 

 tions that meet his needs. 



