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general, and it has been so universally acknowledged as an indispensable acces- 

 sory in advanced microscopic work, that it now justly forms an essential adjunct 

 to all the larger stands intended for scientific research. 



Particulars regarding the construction and application of this apparatus 

 may be found in the detailed directions for use which arc issued with each stand 

 fitted with the ABBE illuminating apparatus. 



The various lens systems - - so-called Condensers - - which are adapted 

 for use with the ABBE illuminating apparatus are all mounted in such a manner 

 that they can be conveniently inserted into the sliding sleeve of the apparatus 

 and may, if necessary, be champed in any position '(see Fig. 11 a ). Since 1886 

 we have invariably added an iris-diaphragm, which facilitates a very gradual 

 variation of the aperture. The smallest opening of the iris has a diameter of 

 about 1 mm, while the largest has one of 32 mm, so that it may remain in its 

 place when either the polarizer or the central-stop diaphragm for dark-ground 

 illumination is in use, or when, according to KOCH'S method, the condenser is 

 used at full aperture. 



In addition to bearing the different types of condensers the sliding sleeve 

 of the apparatus also serves to carry the following appliances, viz: the ordinary 

 cylinder- diaphragm, the iris cylinder-diaphragm, the appliance for 

 centring objectives used as condensers, the illuminating apparatus 

 for spectroscopically decomposed light. 



All stands fitted with an ABBE illuminating apparatus thus give facilities 

 for interchanging all the various appliances mentioned above. 



We only supply the ABBE illuminating apparatus with one 

 of the following Stands: I, II a and IV a . Its adaptation to other 

 stands if at all practicable always entails extensive structural 

 alterations which have to be carried out in our own works. 



The various diaphragms, condensers, &c. used in connection with the appa- 

 ratus are, however, supplied separately as follows: 



1. The Cylinder- Diaphragm, No. 21, Fig. ll c , which is a sliding sleeve 

 fitted with 3 stops yielding apertures varying from 0.5 to 6 mm diameter. 



Price: Marks 4. . Code-word: Pantografo. 



2. The * Iris-cylinder Diaphragm, No. 22. In order to obtain a gradual 

 variation of the illumination when working without a condenser, we have con- 

 structed the iris-cylinder diaphragm. The laminae forming the apertures of 

 these diaphragms are arched in the shape of a cupola so that, when the iris is 

 entirely closed, their edges almost touch the lower side of the object slide. 



Price: Marks 14. . Code-word: Pantuflo. 



