134 Prof. H. L. Callendar and Mr. H. T. Barnes. 



day in either bath, or by more than a tenth of a degree in the course 

 of an observation. From other observations given by Kahle* it 

 would appear as though his cells were subject to a temperature or 

 diffusion-lag of the order of half a millivolt, when the temperature 

 was changing at the rate of 1° C. per hour. From these and other 

 considerations it is evident that Kahle did not aim at an order of 

 accuracy higher than one or two-tenths of a millivolt, and that his 

 formula could not be expected to give correct results beyond the 

 limits of observation. 



Thus, although his formula is practically correct between the 

 limits of his observations, namely 12° and 28° C, it is quite possible 

 that it may be as much as 10 per cent, in error at 0° C. On the 

 other hand, we regard it as quite impossible that our observations at 

 this point should be in error by even a tenth part of the amount, 

 namely 1-J millivolts, by which they differ from the formula of 

 Kahle. Again, although the observations of Glazebrook and Skinner 

 between 15° and 0° C. may have been affected to a slight extent by 

 diffusion -lag, it is plain that the effect of diffusion-lag, if any, must 

 have been to reduce the extent of the change, and could not explain 

 the fact that the change which they observed was so much larger 

 than that given by Kahle's formula, and so nearly in agreement with 

 our own. 



In this Connection it is necessary to refer to an opinion which 

 we have often encountered in conversation and otherwise, and which 

 is possibly still current, namely that the observations of Glazebrook 

 and Skinner are in precise agreement with those of Kahle on this 

 point. For instance, Schuster* quotes correctly Kahle's formula 

 for the mean temperature-coefficient between t° and 15° C, namely, 



a = 0-000814 + 0-000007 (f— 15), 



and states that Glazebrook and Skinner's coefficient (a = 0*00076) 

 refers to a mean temperature of 7'5° C, and is identical with the 

 above at that temperature. This is obviously true if we put t = 7 - 5° 

 in the formula, but not if we put t = 0°. The mistake appears to 

 have arisen from the above formula having been inadvertently 

 described by Kahle as being the temperature-coefficient at t, instead of 

 the mean coefficient between t and 15° C. But although the words, 

 " Fur eine leliebige Temperatur t," used by Kahle, may, perhaps, be 

 ambiguous, the complete formula (K), from w r hich the other is 

 derived, leaves no possible doubt as to the true meaning.]: 

 * Loc. cit, p. 199. 



f ' Phil. Trans.,' A, vol. 186 (1895), p. 458. 



X Note added Sept. 20, 1897. In a more recent number of c Wied. Ann.,' Oct., 

 1896, Kahle states incidentally that he has found by direct comparison the dif- 

 ference 16 - 6 millivolts between 0° and 15°, instead of 15'1 as given by his previous- 

 formula. No details of observations are given. 



