450 Bibliographical Notice. 



with objects which strongly polarize light, thicker plates are 

 requisite for this purpose. I therefore use plates which render 

 the field of the microscope of a red colour of the first to the fourth 

 order. In the examination of the elementary organs of plants, 

 the red of the 1st and 2nd order was sufficient, and I seldom 

 found it requisite to use the red of the 3rd and 4th order. 



These plates are best inserted between the polarizer and the 

 condenser. Hence these pieces of apparatus of the polarizing 

 microscope must be separate and sufficiently apart to allow of 

 the interposition of the plates, which must be capable of rotation 

 horizontally. 



It is scarcely necessary to remark that it is best to cement 

 the plates of mica and selenite between two thin glass plates, and 

 to fix them with paste or some such substance in a circular form. 



In conclusion, a word upon the preparation of organic bodies 

 for examination under the polarizing microscope. — As is well 

 known, many organic bodies can only be examined microscopi- 

 cally under water; these are prepared for the polarizing microscope 

 in exactly the same manner as for the ordinary microscope. In 

 those objects, however, which may be dried without structural 

 change, as sections of vegetable cellular tissue, starch-granules, 

 &c, it is far better to place them in some more highly refractive 

 liquid than water, as oil of turpentine, or Canada-balsam; the 

 more nearly the refractive power of the organic body and of the 

 preservative liquid agree, the more transparent does the object 

 become, and the more difficult to be distinguished under the 

 ordinary microscope, whilst it yields a so much more beautifully 

 distinct image in the polarizing microscope. Very few struc- 

 tures form an exception to this rule — such as the silicious cara- 

 pace of the Diatomacese after the application of a red heat, which 

 in fact strictly speaking cannot then be considered as organic 

 bodies ; these are best examined in the dry state. 



BIBLIOGRAPHICAL NOTICE. 



Ceylon : an Account of the Island, Physical, Historical, and Topo- 

 graphical ; with Notices of its Natural History, Antiquities, 

 and Productions. By Sir James Emerson Tennent, K.G., 

 LL.D., &c. 2 vols. Longman & Co. 



The natural history of the island of Ceylon is a subject so extensive 

 and so important, whether regarded in a scientific or in a commercial 

 point of view, that we must hail with pleasure every new contribution 

 to our knowledge of its animal and vegetable productions ; while such 

 is its mineral wealth and the importance of its gems, that we are no 

 longer surprised at the early traditions of their splendour and pro- 

 fusion having given rise to fabulous stories of their abundance and 



