BETWEEN THE ATOMIC WEIGHTS. 



253 



It is evident, then, that at least one property of the elements varies in the series 

 according to an ascertained numerical law. But, it may be said, this proves nothing, 

 for these specific gravities are connected so closely with the atomic weights that what 

 is true of the one must be to the same extent true of the other. It must be remem- 

 bered, however, that the specific gravities are a distinct set of observed facts, and that 

 the probability of a law is in exact proportion to the number of facts Avhich accord 

 with it. Moreover, the closeness of the connection is unimportant. Whether the 

 value of J) be expressed by a single digit, or by a complicated algebraic formula, is 

 evidently a matter of indifi"erence so far as the confirmation of the law is concerned. 



I regret exceedingly that there are not suflacient data in the case of any of the other 

 properties of the elements in the state of gas to allow comparison, as I feel confident 

 that the law which governs their variation in the series might easily be discovered ; 

 but I look forward to the time Avhen in the general formula pa ^nph the value of p 

 shall be known, not only for the properties of the elements in their gaseous state, but 

 for every property capable of numerical expression. 



In this memoir I have confined myself entirely to the elements, but it is evident 



