702 



SUMMAEY OF CURRENT RESEARCHES RELATING TO 



in use the body-tube is removed and divided, and the two pieces 

 packed in tbe box, which can then be closed by the lid. It can only 

 be used upright, as there is no provision for inclining it. 



Fig. 140. 



Pfaff's Microgoniometer.* — Dr. F. Pfaff's microgoniometer 

 (fig. 141) is practically a theodolite in which the telescope is re- 

 placed by a Microscope. A short pillar carries a large block to 

 which the arc, graduated to 58°, is attached. The block has two 

 sockets in faces at right angles to each other, so that the arc can be 

 set vertically, as in the fig., or horizontally. The alhidade can be 

 clamped at any point of the arc by a screw behind the latter, a slight 

 movement being still capable of being imparted to the alhidade by the 

 other milled head. The vernier reads to 4". The lens is for reading 

 the angles. The Microscope rests in the two frames attached to the 

 alhidade, shown in the fig., and can be depressed or raised at the lower 

 end by a spring screw (so that its axis coincides in direction with a 

 radius of the arc), or moved nearer to or further from the centre of 

 the circle by loosening the side screws in the frames. For micro- 

 scopic objects a stage (fig. 142) is provided, the bent arm of which 



* Pfaff, F., * Das Mikrogoniometer : ein neues Messinstrument, und die damit 

 bestimmten Ausdehnungscoefficienten der Me'talle,' 20 pp. and 1 pi. 8vo, 

 Erlangen, 1872. 



