288 0. G. KNOTT. 



Tlie method of experiment was essentially the same as that des- 

 cril)ed in my earlier paper on nickel. Four stout copper rods, 60 cm. 

 ]ony and 0'7 sq. cm. cross section, were fixed in a vertical position some 

 little distance apart. Their lower extremities were joined in pairs hy 

 two coiled wirei^', one of which was a specimen of nearly pure platinum 

 and the other the cobalt strip that was the special ohject of investiga- 

 tion. The upper extremities of the rods were joined 1)y stout copjX'r 

 sti"i])s to a commutat(^i', which was in connectiori with a Wheatstone 

 Th'ido'e resistance l)Ox of ordinary construction. 



Tn one series of experiments the lower ends of the rods with their 

 c(ii meeting wires were dipped in a vessel of i^il wliich could he heated 

 u]) to a temperature of nearly 240° C. A thermometer, centndly 

 placed so that its Indh lay at the mean level of tlie ]>latinum and 

 rohalt coils, was used for measuring the temperature. The <^il was 

 heated very gradually and was kept briskly stirred until a few seconds 

 before a rending was to be taken. One of the wires was niennwliile 

 thrown irito the Wheatstone Bridge, and the resistance adjusted 

 slightly in advance. The temperature was then allowed to rise very 

 slowly until reversal of the commutator in the galvanometer branch 

 gave no deflection. AVhen the equilibrium was thus attained the 

 thermometer reading was noted. In this experiment chief attention 

 was given to the cobalt ; a few measurements of resistance were made 

 with tlie platinum, sufficient to give the most important temperature 

 coefficient. 



The resistance curves for the cobalt and the pl;itiiuun are shown 

 in the diagram (p. 298), Curves Nos. 1 and 2. All corrections have 

 been carefully applied and tlie resistances are in legal ohms. 



lîy interpolation amongst a number of contiguous measurements 

 the resistance for each of the temperatures 100°, 140°, 180°, 220" C. 

 was calculated as shown in Table I. 



