VI PEEFACE. 



tlie subject is treated at greater length than was permissible in 

 the present instance. 



For a similar reason, and also because it would prove a 

 needless expense, the price-lists of instrument-makers have 

 been omitted. Full particulars relating to the various sorts of 

 microscopes and their accessories can be obtained from any 

 of the leading opticians, who from time to time issue lists con- 

 taining ample illustrations of the most recent improvements 

 in all that pertains to practical working of the instrument. 



In conclusion, the editor finds himself compelled to reiter- 

 ate the well-worn statement, that circumstances over which he 

 has had no control have united to delay the press- work of 

 the volume, and at the end have made its final revision rather 

 hasty. A kind indulgence is therefore asked for any error 

 that may, through oversight, have escaped his notice. 



T. E. S. 



