Mr. J. H. Alexander on the Tension of Vapour of Water. 1 1 1 



reaching from that point to the ordinary atmospheric pressure, 

 and the hist proper tor high temperatures only. He promises, 

 when his experiments in this upper part of the thermometric 

 scale shall have been sufficiently extended and accumulated, 

 to apply himself to the grouping of all three divisions in one 

 comprehensive expression; and from l)is well-known character 

 much may be expected, original and appropriate. In the 

 mean time it would be premature to enter here upon any dis- 

 cussion of what is only provisional. 



To resume, then, in conclusion of this rather protracted 

 memoir ; it seems to me that in the various combinations and 

 comparisons that have been given, the claim of the formula I 

 propose is reasonably well-established, not to be an expres- 

 sion of a law of nature, for to this much it makes no preten- 

 sion, but to represent the pha^nomena of reciprocal pressures 

 and temperatures more exactly and with a more extensive 

 scope, than any that has yet been offered ; and that in so far 

 it is worthy of being taken as paramount to all that have pre- 

 ceded it. How far, in view of the discord yet existing between 

 experimental results of the most recent and reliable observers, 

 it is fit to come in as a substitute for any and all of those results 

 themselves, is not of course for me to determine. I shall only 

 allow myself to notice, then, its remarkable simplicity, and the 

 consequent facility with which it adapts itself to calculation, 

 either with or without logarithms ; as well as the readiness 

 with which, from its elements and form, it suggestsitself at all 

 times to the memory. One important use of a formula, it is 

 to be observed, is in enabling an inquirer in any emergent 

 case, away from books and tables, to extemporise an accurate 

 result ; in proportion to its complexity and arbitrariness, then, 

 it becomes a (juestion of individual strength of memory, and 

 its resort more and more limited. In the present instance all 

 its terms are either given in the very case to be solved, or are 

 physical constants at the foundation of the theory of heat, 

 which I may even say it is impossible for one ordinarily 

 well-informed to forget. And the composition of these terms, 

 thus susceptible of instant recall to the mind, is so plain and 

 necessary even, that it is equally" impossible, with a moment's 

 reflection, for one to go wrong. I believe I am only stating 

 the simple fact when I say that, in these respects, the present 

 formula stands alone. 



Finally, then, I offer for general practical use and reference 

 the following table of temperatures corresponding to pressures 

 in atmospheres and parts through the whole range of experi- 

 ment hitherto. If my labour in so far shall be fortunate enough 

 to meet with the approval of the learned, it will be but an in- 



