be an objective fully up to the standard previously 

 established by the maker, and in all objectives of the 

 same class there must be no noticeable variation. 



The foregoing is given to emphasize the fact that all 

 objectives, particularly the higher powers, are unusually 

 accurate and delicate productions, and that unusual 

 care should be observed in their use to retain their 

 efficiency. This too often is not the case. There \is 

 no reason why under ordinary conditions an objective 

 should not last a life time with daily use. Ordinary 

 care and cleanliness will accomplish this. Neverthe- 

 less, to be more specific, observation of the following 

 simple rules may be of aid : 



Do not allow an object ire to drop. 



Do not allow the front of the objective to come in 

 contact with the cover glass. 



Do not separate its systems. 



- Remove dust occasionally from the front and rear 

 surfaces with clean camel's hair brush. 



After using an oil immersion objective invariably 

 remove the fluid with a soft piece of linen. 



Never at 'low immersion contact with cover over 

 ten hours. 



Use no alcohol. 



