( 183 ) 



how far thermoelements are suitable for the accurate determination 

 of low temperatures (for instance to within V,/ precise), and also 

 by what formula and with how many points of calibration any 

 temperature in a given range can be determined to within this 

 amount. 



§ 3. Modifications in the thermo-elements and auxiliary apparatus. 

 We shall consider some modifications and improvements which 

 have not been described in § i of Comm. N". 89. The first two 

 {a and b) have not yet been applied to the element with which 

 the following measurements are made, but they have afterwards been 

 applied to other elements and so they are mentioned for the sake 

 of completeness. 



a. If we consider that the thermo-element in different measurements 

 is not always used under the same circumstances, e.g. is not immersed 

 in the bath to the same depth etc., and that even if this is the case, the 

 time during which this is done at a constant temperature will not always 

 be so long that in either case the same distribution of the temperature 

 will be brought about in the metallic parts of the element, it will prove 

 of the greatest importance that care should be taken, that the tem- 

 perature of the juncture, given by the electromotive force, differs 

 as little as possible and at any rate very little from that of the 

 surface of the copper protecting block, that is to say that of the 

 bath. 



The construction of the place of contact shown by fig. 1 

 is a better warrant for this than that on PL I of Comm. 

 N°. 89. The wires a and b are soldered on the bottoms 

 of small holes c, bored in the protecting block and are 

 insulated each by a thin-walled glass tube. If the con- 

 struction of PI. I Comm. N". 89 is not carried out as it 

 should be (whether this has succeeded will appear when we 

 saw through trial pieces) and consequenlly the juncture is 

 a little removed from the upper surface of the block, it may 

 be easily calculated that, owing to conduction of heat along 

 the wires while the thermo-element is immersed in 

 li(jnid oxygen a difference in temperature of as much 

 as one degree may exist between the place of contact 

 and the block. When the elements are used under 

 other circumstances, this difference in temperature will 

 have another value and hence an uncertainty will come into the 

 determination of the temperature of the block. Perhaps that also a 

 retardation in the indications of the element will be observed. 



13* 



