7. =Objective 1 a= with adjustable mounting and changeable magnification. It is an excellent objective of low power for general purposes, having a comparatively short working distance. 8. =Objective 1 b= with changeable magnification of lowest power, as far down as two diameters. It serves for drawing extended sections and specimens. 9. =Saccharimeter after Mitcherlich= improved form. 10. =Trichinoscope=, projection-apparatus of strong and simple construction. =Preface.= Our American Branch house in New-York under the management of Mr. Wm. Krafft has now been established for over 10 years. This period has witnessed a gradual development of our business in the United States, making it necessary to establish some years ago a Western Branch in Chicago of which Mr. R. Gibson has charge. The cordial reception our firm received has been most gratifying and we take this opportunity to thank our many patrons for their kind consideration. It is our aim to co-operate with the scientists and construct new apparatus to meet their needs or improve others wherever this is possible. The foregoing list of additions and improvements made since issueing our last catalogue is proof that we spare no time nor labor to hold pace with the increased wants of modern times. We have now manufactured and sold over 71000 compound microscopes and 31000 oil immersion objectives, a large number of which are used in the laboratories of Universities, Colleges, and other Educational Institutions of the United States. We are prepared at New-York and Chicago to repair our instruments or make alterations at short notice and at lowest prices. The optical part of a microscope should invariably be sent to the maker, as he is best in a position to repair same and has an added interest to bring a lens back to its original quality or even improve it. Microscopes, bacteriological apparatus and all other scientific instruments or preparations expressly imported for use in educational institutions are exempt from duty. Catalogues may be had on application by addressing: =ERNST LEITZ,= NEW-YORK CHICAGO 411 West 59th Street 32 Clark, Cor. Lake Street. =Objectives and Eye-pieces.= In the manufacture of our objectives only such glass is employed as has been subjected to the most rigid scientific tests. By these the exact index of refraction and the exact degree of dispersion of the glass are determined, and with these data available it is possible to very perfectly correct both spherical and chromatic aberrations while still making use of wide angular apertures in the objectives. The precise mathematical calculation, combined with accurate systematical working and testing methods, make it possible for us to guarantee our objectives to be all of equal and excellent quality. Every objective before leaving our hands, is subjected to the most careful test, and only such lenses as are of the highest grade, are sent out.