( 301 ) 



The investigated wii-e covenMl two of these fylindei's r', and r, 

 (see tig'. J, PI. 1), llic one tittin^;- into the olhcr mid h'a\ ing a jacket 

 of abont 2 mm. Cor tlie eiiruhilion of tlic n(|iii(Is. A third eviiiider 

 c, ronnd tlu>s(^ two ser\ed to protect liic w ir<'. 



Tlie cylindei's res! on a coijper star willi 'A Icctli <l in which 

 conccutrical gi-ooves arc ma(h' lo hold the ^hiss c\ HikUm-.s. At llie 

 othci' end each of the cylinders, bv means of cojtpcr lidges <'^, c.^ 

 and <'.^, lying' on the glass rim, is pressed against the star bv means 

 of a tightening rod /' and iiuls ƒ/,, ƒ/., aiid ƒ/.,. lliiis lurmiii^- one 

 tightly comiected whole. As the lidges <\ and c., and also rlie lower 

 star (/ served at I he same time as comiectix'c [)laces for the wii-e, 

 they were insnlated from the tightening rod and the Jinis by glass 

 cylinders //^ and //,, and plates of mica l^, /'.. and /.,. 



The winding and the mounting was done in the following wav. 

 We began by tixing the inner cylinder Cj betweiMi the slai- and the 

 ridge <\, the wire was soldered on to the ridge /^^ and led downwards 

 along the groove of the screw-thread on the cylinder. At llie boltom 

 it was soldered on to the star. Then the second cylindei- was placed 

 ronnd it, the wire was turned nj) wards along it and fastened to 

 e.^. If the two screws in the glass are \vound in the same sense, the 

 wire is almost free from induction. (Cf. the platinum thermometer 

 of the previous paper wdiere this was attained in a dilfei-ent manner). 



As in the case of the platinum wire which was treated in the 

 previous [)aper, there were 4 lea<ls. Kor the method with the 

 ditferential galvanometer (cf. § 4) it does not matter that they have 

 little resistance, hence wires of i mm. were taken, flattened over the 

 last 5 (;nis. The entire a[)paratus was suspended by a copper tube k, 

 which was screwed on to the tightening rod /', and which, in order 

 to prevent too much conduction of heat along it, had a piece of 

 ebonite inserted in it (not shown in the drawing). 



§ 3. Deter m.b tat ion of tke zero. The zero was determined in the 

 same way as described in ('omm. N". 77, wlien thin leads were 

 used. Besides with the gold wire, deterjiiinations were also made 

 with a copper and a silver wire. A single determination never 

 olfered any difficulties. With copj)er, however, the values determined 

 at different times did not agree. They showed a i-egular increase of 

 the resistance at 0^ C. This must probably be ascribed to a chemical 

 process. Copper oxydises so easily that the greatest precautions must 

 be taken to avoid moisture during the storage. If in distilling the 

 insulating liquid into the zero-vessel tlie vapour was passed over 

 [)hospliorous |>entoxide and if care was taken that while the wire 

 was kept, the air could oidy enter over phosporous pentoxide, we 



