The German glasses of to-day afford satisfactory evidence both of skill and workmanship displayed in their production. Their cost is greater, then, for the reason given, as will be seen on reference to Continental catalogues. The dry series of objectives cost somewhat less, a 1/2-inch (numerical aperture 0·30) can be had for £1 10s., and a 1/6-inch (numerical aperture 0·65) for £2. On the other hand, the apochromatic series rapidly increase in price as the numerical aperture approaches the limit of numerical aperture 0·40. The best of Zeiss’s series are the 12 mm. (1/2-inch) and the 3 mm. (1/8-inch), numerical aperture 1·4, both of which possess the optical capacity assigned to them. These objectives are undoubtedly the finest to be met with in the workshop of any optician. Achromatic objectives of Continental manufacture have been as much improved as those of English make by the introduction of the newer varieties of glass, as already explained, while a new nomenclature has sprung up in consequence. We now have semi-apochromatic and parachromatic. The German opticians have followed Zeiss’s lead, since almost the same series of objectives are given in the catalogues of Leitz, Reichert, and Seibert, while the quality of both dry and immersion objectives is found to be much the same. The low price of Reichert’s immersion objectives should be noted, as their performance is quite perfect. A 1/12-inch (numerical aperture 1·30) of Leitz’s, with which I have worked at _bacteria_, has given me much satisfaction; supplied by Watson and Baker at £5. A 1/12-inch dry objective by the same maker (numerical aperture 0·87) costs £3, and a water immersion 1/12-inch (numerical aperture 1·10) £3 5s. Leitz reminds me that it requires a good lens of from six to seven hundred magnifying power for the examination of bacteria. For this reason he has constructed a new form of lens, a 1/10-inch oil-immersion of 2·5 mm. focus, for the purpose of adding to the resources of bacteriology. This lens necessarily has a lower magnification than his former 1/12-inch oil-lens, but as it is less costly to manufacture it is sold at a smaller price. The before-mentioned 1/12-inch, with a No. 3 compensating eye-piece, gives a magnification of over seven hundred or eight hundred diameters. To secure the best results in using the higher powers of Leitz’s, from No. 5 upwards, a cover-glass of 0·17 mm. in thickness should be used, and care taken to make the length of the draw-tube equal to 170 mm. This length of tube should be adhered to in the use of this optician’s oil-immersion lenses. If the microscope be provided with a nose-piece, the draw-tube should be drawn out to 160 mm.; in its absence it should be set at 170 mm., a deviation of 10 mm. or more from the correct tube-length deteriorates from the value of Leitz’s oil-immersion objectives as of other opticians. It is suggested that the German apochromatic combination of three cemented