38 SELECTION AND USE 



greatly increased in its effects \vlien it reaches the upper end of 

 the body. In addition to this, the unsupported part of the 

 body acquires, by each movement, a momentum which reacts 

 powerfully on the lower part, and consequently on the ob- 

 jective. 



These defects have induced Messrs. Koss & Co. to bring out 

 a new pattern designed after the Jackson model. This design 

 has been carefully worked out by Mr. Wenham, and is certainly 

 very beautiful in appearance, and very efficient and convenient in 

 use. Our readers will therefore bear in mind, that all micro- 

 scopes made by Ross & Co., are not made on the "Boss 

 model." 



It is not our purpose to enter here into the details of the con- 

 struction of the stage, and the various means of illumination 

 which accompany this microscope. For these we refer to the 

 extensive illustrated catalogues, which may be obtained from 

 the manufacturers. 



Browning's New Model. The importance of being 

 able to rotate the object in relation to the illumination is gen- 

 erally recognized, and in almost all the better class of stands, 

 full provision is made for this. It has always been difficult, 

 however, to secure perfect coincidence of the centre of rota- 

 tion with the optic axis. In the better class of microscopes, 

 made a few years ago, the makers depended upon perfect work- 

 manship to secure this end, and consequently a satisfactory rota- 

 ting stage was to be found only in the very best instruments. 

 After all, however, perfection is not to be found, and even the 

 best stages of this kind were very liable to get out of order. To 

 obviate this, Mr. Browning has constructed his stand with the 

 stage in two pieces, the lower part being connected with the 

 foot, and the means of illumination, while the upper part, which 

 rotates on the lower, is rigidly attached, to the arm which 

 carries the body. In this way the body, arm, and stage may 

 all be rotated in relation to the illumination, and for ordinary 

 purposes this answers very well. When polarized light is used, 

 however, it is obvious that it is impossible to rotate the object in 

 relation to the polarized ray, without also rotating the analyzer, 

 and, aa every one that has worked much in this direction 



