Mr. J. H. Alexander 0)i the Tension of Vapour of Water. 105 



whereby to compare the merits of divers proposed formulae as 

 well as his own. It is true this group contains, among others, 

 one of the very experiments which I have in the preceding 

 memoir noted as faulty, and as being differently recorded in 

 the two tables ; but I have not allowed myself to exclude it 

 here any more than before. Also for his comparison, M. 

 Dulong has taken the reading of only the maximum thermo- 

 meter, which represented the actual temperature of the water 

 in the boiler. For the present purpose, however, as in the 

 case of M. Regnault's experiments, it is necessary to take the 

 other thermometer-reading also and register the variation of 

 the extremes, as under. I have entered the pressures here in 

 English inches, since they have already been reduced for the 

 comparative table ; but to save unnecessary calculations, I re- 

 tain the temperatures in Centigrade degrees. 



equivalent to a mean error of +0°'28 F., arising from the 

 uncertainties of temperature. 



To contrast this with the formula, we have from the same 

 experiments as under: — 



