ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



359 



on which rests a steel pin fixed to the under side of the arm, thus form- 

 ing a perfect-fitting slide. 



The carriage is actuated by a micrometer screw working against one 



^m?v 



Fig. 73. 



end of the steel cylinder, the latter being kept in contact by pressure 

 with the finger on the other end. The screw is of 0*5 mm. pitch, with 

 m head divided into 100 parts, and a traverse of 

 30 mm. 



The instrument is also made without the 

 micrometer screw, in which case a millimetre 

 scale is fixed to the top edge of the base, the car- 

 riage being furnished with a vernier reading to 

 0*05 mm. The Microscope is provided with a 

 Ramsden eye-piece with cross wires. It is held 

 in position against four points by a flexible steel 

 spring, and the vertical cradle that supports it 

 will receive any other Microscope-tube in place 

 of the one supplied. 



Short Table Cathetometer. — This instru- 

 ment (fig. 74), made by Messrs. W. G. Pye and 

 Co., is constructed on the geometric slide prin- 

 ciple. The base, provided with three levelling 

 screws, carries a steel rod \ in. in diameter, with 

 a millimetre scale divided on it, which can be 

 read when the telescope is in auy position. A 

 brass ring with V bearings, carrying-the telescope 

 cradle and micrometer, fits on the column, and is 

 capable of being revolved without altering its 

 height. The V's in this annular ring are kept 

 against the column by a spring on the opposite 

 side. 



The micrometer slide consists of two steel rods carried by the ring. 

 Against one, which is fixed to the ring, one point of the telescope cradle 

 is pressed by a spring. The other is fixed to the telescope cradle, and 

 works in two V's cut in the annular ring. One end of the latter rod 



Fig. 74. 



