One would naturally imagine that the minute lenses used in microscope objectives should be cheaper in comparison than the larger lenses used for photography or in telescopes, for it is always more difficult to make minute articles than large ones. As a matter of fact, even allowing for the greater amount of material used in the larger lenses, quality being the same in both cases, they are far more expensive than the smaller microscope lenses; the reason being that it is exceedingly difficult to obtain a perfect specimen of large size. The difficulty arises not only in the actual manufacture of the glass but in the subsequent operations of cutting, grinding and polishing when fractures are very liable to occur. From this brief account of the manufacture of optical glass it is clear that a good lens is always worth a high price. Its components must be of the purest quality obtainable, the process of manufacture requires highly skilled labour and it is laborious and exacting work. Constant attention is needed from start to finish and much of the glass is never sufficiently good to pass the rigorous tests which it must undergo. Lastly, in the final preparations of the completed lens, mishaps are frequent. Added to all these trials of the lens maker is the one outstanding fact that the process can never be hurried at any stage, the efficient annealing of optical glass is one of the most important stages in its manufacture. A very full account of the manufacture of optical glass is given in the _Encyclopædia Britannica_, whence much of our information in this chapter is derived. CHAPTER XXII THE CHOICE AND USE OF APPARATUS AND ACCESSORIES In this, our concluding chapter, we propose to give a few hints upon the choice and use of the microscope and its accessories, to enlighten our readers concerning stains and staining and to add such other information as is likely to be useful, information which is better supplied in a chapter of its own than scattered about our pages and probably overlooked. The most important question concerns the choice of a microscope. In a book of this nature it is obviously impossible to recommend the wares of any one maker. Some firms are celebrated for the good wearing qualities of their instruments, some for the delicacy--not fragility by the way--of their fine adjustments and our readers must select their maker for themselves. One thing we strongly advise, be patriotic and select a British maker, it is not only a question of patriotism but of self interest, for in many respects the British instruments lead the world. Most of the manufacturers advertise in such papers as _Nature_, they all print excellent catalogues, a perusal of which may be a useful preliminary.