( 29G ) 



Physics. — „Mcasi(re)H(iits on f he iiiu(/neiic rotatory dispersMii of 

 gases.'' By Dr. L. H. Siertsema. (Communication W. 4G 

 from tlie Physical Laboratoi'v at Leiden by Proi'. II. KaMER- 

 LiNGH Onnes.} 



(Eead in tlie meeting of December 24"' 1898.) 



1. Description of the apparatus. Tlie figures given licre are intenrleil 

 to complete and to illustrate the description ') of the apparatus used 

 in the investigation. 



Fig. 1 shows a general view of the whole apparatus and of the dif- 

 ferent electric circuits, fig. 2 — 5 show the two nicolbearers in section. 

 For the description of these I refer to the communication of March 

 189G, for the coils to that of June 1893, for the optical apparatus 

 and several other details to that of January ]8V)5. The description 

 of the mirror-reading of which fig. 6 gives a general view, and 

 fig. 7 and 8 represent some details, may also be found in the latter 

 communication. Fig. 9 represents the high-pressure tubes with the 

 manometer, fig. 10 shows one of tlie high-pressure stopcocks that 

 have been used. Fig. 11 represents a section of the system of tubes 

 for the cir(!ulation of water together with the thermometers. 

 EXPLANATION OF THE FIGUEES. 



Fig. ]. General arrimyement of the cqjparatiis. A collimator, B smaller nicol- 



liearer, C and 1> coils, Ji greater nicol-liearer, T F experimental tnlie, 

 G screw for the rotation of the smaller nicol-bearer, which is connected 

 with it by the steel wire RH, guided by the pulley 0; / weight for 

 pulling back the nicol-bearer. L vertical graduated glass scale on which 

 the rotation of the mirror N is read in the telescope K by means of 

 the intermediate mirror M, P prism and Q telescope of the spectro- 

 meter, X switchboard where the currents are supplied, y arc-lamp, the 

 motor of which is fed through a thinner wire originating from terminal 3, 

 a resistance and /3 amperemeter in the arclamp-circuit, e switch for trans- 

 ferring the current from the coils to the resistance Y or for breaking the 

 current, J commutator for reversing the current in the coils, Z switch 

 by means of which the whole apparatus can be switched out except 

 the shunt T, which sends a derived current to the galvanometer V 

 with the stop-commutator U. 



Fig. 2 — 5. Section of the two mcol-bnirers. a nicol, mounted in a cylinder q, and 

 kept in its place in the nicol-bearer m by means of a ring i with adjusting 

 screws, f experimental-tube, on to which the tube with flange n has 

 been soldered and which is fastened to the nicol-bearer by the nut g 

 with the stuffingriug t, e connecting nut for the high-pressure conduit, 

 // level, flange with six bolts and nuts ;;, c glass plate with nut d 

 and leaden-stufting ring r, which is prevented from being forced out by small 

 rings «, // handle to wliich the steel wire //. (comp. H tig. 1) is fastened. 



1) Verslag Kon. Akad. 1893/9-t, p. 31; 189-1/95 p. 230; 18'J5/9G p. 294, 31 7; 

 1S9C,97 p. 131, 132; Comm. Phys. Lab. Leideu N", 7, 15, 24, 31. 



