905 



§ 2. Method. The measurements were made hy the attraction 

 Hictliod, with a vertical cylinder of the substance to be investigated. 

 One of the extremities of tlie cylindei' is phiced in the middle of the 

 interferrum of an electromagnet. As ii! the apparatus previously 

 constructed by us') the cylinder was attached to a vertically running 

 carrier, and the forces were measured by a zero-method ; in this 

 the moditication introduced by OosTKiuiris'} wos made use of, viz. 

 the current through the electro-magnet was regulated, and therefore 

 the field adjusted, until there was equilibrium with marked weights. 



While thus the magnetic pari of the expoii-imeuls is about the 

 same as that of the previous ones, the arrangement of the actual 

 experimental object demands a number of special apparatus and 

 precautions. A homogeneous mixture must be prepared of known 

 proportion, and in a proportion chosen at will, of two substances, 

 which are gaseous at ordinary temperature, and whicli are condensed 

 in the experimental tube. 



In the first place a communication must be made through the 

 closed outer cover of the cryomagnetic apparatus (see desciiption 

 loc. cit.) with the apparatus for mixing and measuring the gases. 

 For this purpose, the glass tube A (see tig. J), which forms the 

 central part of the carrier, is bent round three times rectangularly 

 at B ; further it beai'S a horizontal tap (', and terminates in a 

 horizontal ground joint D, in which fits the ground extremity of 

 the tube E, which protrudes outside. This tube is enclosed in a thick 

 but elastic india-rubber covering, and can be pulled back about 

 2 centimetres, from outside, and made fast in this new position ; 

 in this way the coimection with the carrier, can be made ; or the 

 latter can be left quite free, without the cover being opened. In the 

 same way the tap C can be mani|)ulated from the outside by 

 means of a similar arrangement F. 



The necessity of the mixture being homogeneous, entails vigorous 

 stirring inside the experimental tube (the cylinder A*, at the lower 

 end of the carriei-). Even when the mixture is homogeneous in the 

 gaseous form, the oxygen which condenses more easily, will tend 

 to collect at the bottom in the carrier ; this difHieuity is overcome 

 by using a stirrer consisting of a very long thin glass capillary tube 

 G, terminating in a small disk // (the actual stirrer), which carries 

 a little piece of iron {[{) at the top ; the whole of which can be 

 moved up and down through a distance equal to the height of the 

 experimental tube. This movement is set in motion by the atliaction 



1) See H. Kamerlinoh Onnes and Alb. Perbier, Comm. No. 139a. 

 ^) E. OosTEBHUis, Comm. N'^. 1396. 



58* 



