APPENDIX. 751 



made, and remarkably cheap at the price, 6 6*. ; we very 

 cordially recommend it for general use. 



Mr. Ladd has lately effected improvements in the 

 manufacture of his instruments in mechanical details, 

 and in obtaining a perfect centre of gravity. In his best 

 instrument, such as that represented in fig. 362, he has 

 taken great care to obtain a perfect balance in any position, 

 even when placed on its horizontal axis ; no instrument 

 can be better adapted than this to all the wants of the 

 microscopist, and which is one combining many of the 

 advantages of the more expensive forms. 



Nachet and Hartnack of Paris, and Merz of Munich, 

 hold an almost equal rank as makers of first-class micro- 

 scopes, and in point of excellence of workmanship 

 fairly rival those of English makers. Hartnaek's latest 

 improvement consists in an exquisitely-fitted concentric 

 stage, which works with marvellous neatness and pre- 

 cision. Nachet has also effected considerable improve- 

 ments in his circular stage, as well as in the arrangement 

 of his binocular form of body; for fuller particulars of 

 which we must refer the reader to the Monthly Micro- 

 scopical Journal. 



IMMERSION OBJECTIVES. 



Messrs. Hartnack and Merz and others have likewise added 

 greatly to their well-earned reputations by the construction 

 of immersion objectives of a very superior order. We have 

 had especial opportunities of comparing the respective 

 merits of Hartnack's -f$ and -^, Merz's ^, and Noberts's 

 -^, of which we can speak in the highest terms of praise. 

 All work through ordinary thick glass covers with 

 great facility, and are therefore adapted either for the 

 examination of pathological specimens or for the most 

 delicately-lined test-objects. The low price at which they 

 are sold is no unimportant consideration to the student in 

 microscopical science ; the -^ of either Hartnack or Merz 

 can be purchased for about 6 6s., while their other powers 

 are equally cheap. Amici nearly fifty years ago demon- 

 strated the value of the immersion system : and Soemmering, 

 writing of one of Amici's microscopes, observes : " Its 

 magnifying power, and the admirable precision and clear- 

 ness with which the object is seen, seems astonishing." 



