POSITION OF OBSERVES. 261 



its maker. And why? Simply because the purchaser 

 was as incompetent to " handle " the instrument, as 

 perchance he might have been to manipulate a piano- 

 forte or church organ. And then again through his 

 ignorance he might have possibly ordered the very 

 glass he did not want. What would we say to the 

 invalid who on summoning the attendance of the physi- 

 cian should undertake to dictate as to the treatment! 



Again, we have often been requested b}' our friends 

 and visitors to examine objectives and give our opinion 

 thereon ; and, as a rule, five minutes Avill suffice for this. 

 But, says the owner, "you must be prejudiced against 

 my glass. No man could give a well grounded opinion 

 in the few moments you have occupied." Nevertheless, 

 we have given hundreds of just such opinions without 

 having had occasion to modify or retract, and here is 

 an illustration showing that time spent in the study of 

 objectives is neither totally lost nor without its compen- 

 sations. We reiterate, let the microscopist understand 

 well his tools, and in the hope of being at least some 

 assistance to the student we are ready to proceed with 

 our instructions. 



In the lessons which follow the reader is presumed to 

 employ a wide apertured one-fifth, one-sixth or one- 

 tenth immersion. We shall try, as far as possible, to 

 make them applicable to the use of any good glass hav- 

 ing air angle up to 175. The higher balsam angles 

 will, however, when attainable, be the better instrument, 

 with which, too, the instructions will be the better un- 

 derstood. The student is also reminded that with the 



