NO. 3 THE KAMPOMETER ABBOT 3 



The figure shows the principal features of the kampometer ^ in 

 diagrammatic fashion. The two equal groups of suspended magnets, 

 a, h, of opposite polarity, are fastened so to be as nearly as possible 

 in parallel vertical planes, as indicated just below the suspension at 

 c, where one is supposed to be viewing them nearly from above, but 

 neglecting the curled stem which connects them. Each group is 

 cemented to a short, thin, vertical rod of glass. (/, c, and these two 

 rods in turn are cemented to the ends of the bimetallic curled strips, 

 /, g, oi opposite curvature. The two curled bimetallic strips are con- 

 nected by a third short, thin rod of glass, //, so that the whole forms 

 a suspension similar to that of an astatic rellecting galvanometer. A 

 small mirror, /, is affixed to the glass rod, <?, in the usual way to indi- 

 cate deflections of the system. 



The suspended system hangs within a vacuum tube having a side 

 window, as indicated in the plan view at k. On either side of the 

 evacuated tube are electromagnets A, B, C, D, adapted as will be 

 explained below to produce any desired degree of astatic sensibility. 



Under the influence of a beam of radiation falling on the curl, /, 

 the magnet groups, before parallel, are rotated with respect to one 

 another. This changes the efifective polarity of the system as indicated 

 at y. Consequently the system tends to turn through 90° so that the 

 new polarity may coincide with the direction of the magnetic field. 

 Being opposed by the torsion of the quartz fiber and by inequalities 

 of magnetization of the two fields the system actually takes up some 

 such position as shown at /. 



I find it more convenient to use electromagnets rather than perma- 

 nent magnets to control the astatic condition of the system. It is 

 necessary to change the relative strengths of the upper and lower 

 fields, and also to rotate these two fields with reference to each other, 

 in order to raise the astatic condition of the system to any desired 

 degree. It is very easy with electromagnets to make relative altera- 

 tions of the two fields in large or small steps by resistance-box changes. 

 Both fields, of course, are operated in parallel from a common storage 

 battery, and changes in the distribution of the current are produced 

 by operating resistances in shunt circuits. In order to produce the 

 relative rotation of fields which is required, quick and slow adjust- 

 ments of the azimuth of the pair of magnets. C, D, are provided by 

 means of tangent screws and a clamped tangent arm in the usual 

 way. This rotation requires very fine adjustment to secure high 

 sensibiHty. 



' From the Greek words Kafiirrj, a bend, and fxerpew, to measure. 



