1892.] and Measurement of Small Electrostatic Capacities. 7 



sheet brass. The set B are all squares, the bottom one of which is of 

 much thicker metal than the others, and tiie plates of this system 

 are one less in number than the plates of system A. The four bolts 

 binding together the plates of each system pass through well-fitted 

 holes in the corners of the squares ; and the distance from plate to 

 plate of the same set is regulated by annular distance pieces which 

 are carefully made to fit the bolt, and are made exactly the same in 

 all respects. Each system is bound firmly together by screwing 

 home nuts on the ends of the bolts, and thus the parallelism and 

 rigidity of the entire set is secured. 



The two systems are made up together, so that every plate of B is 

 between two plates of A, and every plate of A, except the two end 

 ones, which only present one face to those of the opposite set, is 

 between two plates of B. When the instrument is set up for use, 

 the system B rests by means of the well-known " hole, slot, and plane 

 arrangement," * engraved on the under side of its bottom plate, 

 on three upwardly projecting glass columns which are attached to 

 three metal screws working through the sole plate of system A. 

 These screws can be raised or lowered at pleasure, and by means of 

 a gauge the plates of system B can be adjusted to exactly midway 

 between, and parallel to, the plates of system A. The complete 

 leyden stands upon three vulcanite feet attached to the lower side of 

 the sole plate of system A. 



In order that the instrument may not be injured in carriage, an 

 arrangement, described as follows, is provided by which system B 

 can be lifted from off the three glass columns and firmly clamped to 

 the top and bottom plates of system A. 



The bolts fixing the corners of the plates of system B are made 

 long enough to pass through wide conical holes cut in the top and 

 bottom plates of system A, and the nuts at the top end of the bolts 

 are also conical in form, while conical nuts are also fixed to their 

 lower ends below the base plate of system A. Thumbscrew nuts, /, 

 are placed upon the upper ends of the bolts after they pass through 

 the holes in the top plate of system A. 



When the instrument is set up ready for use these thumbscrews are 

 turned up against fixed stops, g, so as to be well clear of the top plate 

 of system A ; but when the instrument is packed for carriage they are 

 screwed down against the plate until the conical nuts mentioned 

 above are drawn up into the conical holes in the top and bottom 

 plates of system A ; system B is thus raised off the glass pillars, and 

 the two systems are securely locked together so as to prevent damage 

 to the instrument. 



A dust- tight cylindrical metal case, h, which can be easily taken off 

 for inspection, covers the two systems and fits on to a flange on 

 * Thomson and Tait's ' Natural Philosophy,' 198, example 3. 



