( 291 ) 



which was modified as described in § 2 ('oinni. N". H'A. In (his 

 cryostat a vacuuin vessel was placed iiisi(k' of fJ^ (IM. I, Coiniii. 

 N". 51), which vacuiiui vessel by means of cork was pressed aL!,ains( 

 the w^alls of B^ (cf. end of § 2 and also Pis. T ajid II of (\»mm. 

 N». 83). The inner wall look (he i)lace of 3., in Pi. 11, ('omm. X". <S;] 

 (the same parts of Comms. N". 8.3 and N". 77 are marked w i(li (he 

 same letters). 



These preliminary experiments had shown, that, after rc[»ea(ed mea- 

 surements at the lowest temperatures, the original value was again 

 found for the resistance at 0° C, hence that the platinum wire, though 

 its expansion dilfered from that of glass, was not lengthened and that 

 it also remained properly in the notches. Further it had become clear 

 that an accurate comparison of the two thermometers was only |>os- 

 sible when the temperature of the bath was kept constant with the 

 utmost care, and there we met with the difliculties treated in § 2 of 

 Comm. N". 83. It was attained by arranging the cryostat as described 

 in § 5 of Comm. N". 83. It may moreover be remarked that 

 the liquid gas was always kept higher than 5./ (Comm. N". 83, 

 PI. II) ; else, notwithstanding the level in and outside the protecting 

 cylinder would go up and down through the motion of the stirrer, 

 no circulation would be produced. 



The course of a measurement was as follows. As soon as the cir- 

 cumstances under which we desired to make a measurement were 

 established, the resistances of the leads were determined. tlu>n the 

 resistance of the platinum wire was adjusted and, by giving signs 

 to the assistant charged with the reuulatioii of (he prcssur(\ care was 

 taken that this resistance, and hence the same (eiii|»ei-a(ure, were 

 maintained. After about ten minutes we began, while cons(an(ly 

 reading the galxanometer, the measurements with (he hydrogen ther- 

 mometer and coiitiiiued tliem until (he li(|iiid was eva])ora(ed or 

 until wx^ deemed (ha( snI'liciciH (la(a were ob(ain(Ml. Al liic cud (he 

 measurement of (he resis(ance of the leads was repeated. 



The observer a( (he gal\an()uic(ei' had, thei-efoi-e, oidy to look 

 after the continual closing and brcakiiig of the cui-rents and (he 

 noting down of (lie xaiiics of (he gal\aiiomc(cr ivadings and of (he 

 time belonging to (hem. Af(erwards (he (Icllcclious were deri\ed from 

 this (see PI. Ill Comm. N". 'S3) and (he mean dellec(iou dnrini'- (he 

 time of observation was found by means of a plauimeter. 



§ (i. Xi/ii tijicr the nicasui-i'iih'iils. \\\ a (00 rapid decauladon of 

 li(pnd oxygen, uuuiei-ous biii-sts had indorliinalely come in (he c\lind<'r 

 of the resistance. To repea( wi(h i( (he abo\ e described opera(ions 

 for the determination of the zero seemed rather dangerous, especially 



