ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



499 



plate. The slide is actuated by the rounded end of this micrometer 

 screw, and at the other end presses against the spring and rod E. All 

 movements involved are exact and free from looseness. The screw and 

 rod are accurately co-axial. A graduated drum F regulates the move- 

 ment of the micrometer screw, and a pointer attached to the ground 

 plate facilitates reading. The graduations are so arranged that zero 

 corresponds to the position where the tube-axis coincides with the centre 

 of the rotatory stage (i.e. the medium position) ; whole rotations of the 

 micrometer screw are read off on the pointer, while fractions are given 

 by the drum. One rotation of screw gives a length-movement of • 5 mm. 

 The drum is 66 mm. in diameter, and its circumference is divided into 

 500 parts, so that a rotation of one division gives a slide-movement of 



-»>*8*|*- 18 — * 



Fig. 91. 



about 1 ft ; thus readings can be taken directly to the thousandth of a 

 millimetre, and, by estimation, to the ten-thousandth. The apparatus 

 affords five complete rotations of the drum forwards and backwards, 

 and therefore a total movement of the stage of 5 mm., which is sufficient 

 for the purpose. The authors point out that the apparatus would also 

 be serviceable for centring objective and ocular, and for orientating 

 objects. Satisfactory tests of accuracy were made. 



Hirschwald, J. — Tiber einneues Mikroskopmodell und ein " Planimeter-Okular " 

 zur geometrischen Gesteinanalyse. CentralbL f. Mineral., 1904, p. 626. 



Kase-vturm — Neue Trichinenschaumikroskope. 



Zeit.f. Fleisch. u. Milchhygien, Bd. xiv. (1904) p. 269. 



jNIeyer — Das Ultramikroskop. Kosnios, Bd. i. Heft i. 



Rinne, F. — Le Microscope polarisant. Traduit par L. Pervinguiere, avec preface 



par A. de Lapparent. Paris, 1904, 160 pp. 



(2) Eye-pieces and Objectives. 



New Formula Object-glass. — Messrs. Leitz, of Wetzlar, have lately 

 introduced two new object-glasses, viz. a \ and ^, on an entirely new 

 plan. They may be described as semiapochromats containing fluorite. 

 In these we have a new type of lens, which is neither a semiapochromat 



2 t 2 



£t Lt m 



