12 PREFACE. 



into detail respecting it ; and, with a view of render- 

 ing- it as available as possible, have printed in the 

 Appendix Mr. Talbot's highly interesting papers 

 upon the polarizing properties of crystals. Although 

 this is in itself almost a new instrument, a great 

 deal has already been accomplished by its means, 

 and a great variety of the hidden phenomena of 

 nature most beautifully displayed. 



The kind consideration bestowed upon the first 

 edition by men the most distinguished in science, 

 who had turned their attention to this subject, and 

 the interest now so generally felt in microscopic 

 researches, induce me to hope that the present 

 volume a large portion of which has been re- 

 written, expressly that it should contain the latest 

 improvements will be favourably received. 



ANDREW PRITCHARD. 



162, Fleet Street, London. 



