382 Prof. H. E. Armstrong on Low-Temperature Research 



side has held that the effect is due to " atmospheric " influences and 

 that it is produced at the expense of some amount of chemical change ; 

 the other has regarded it as a purely inductive effect, although on 

 this point again there is a difference of opinion as to whether or no 

 the metals alone are concerned. 



His suggestion may also be extended to a subject which occupied 

 a large share of Faraday's thoughts — that of inductive cajmcity. The 

 so-called specific inductive capacity of a vacuum was measured by a 

 Committee of the British Association in 1880, soon after the intro- 

 duction of the Sprengel pump had led to an improvement in the 

 means of securing a high degree of exhaustion. The value was but 

 slightly lower than that deduced previously from measurements in 

 ordinary vacua (B.A. Report, 1880, p. 197). The question is whether 

 in the highest attainable charcoal vacua the value would differ from 

 that obtained under more ordinary conditions. 



Faraday thought of induction " as in all cases an action of con- 

 tiguous particles " ; the power of propagation possessed by so-called 

 insulators he called their Specific Inductive Capacity. But, as Tyndall 

 has insisted, Faraday regarded insulators and conductors as merely the 

 opposite terms in a series. The insulators in common use, we now 

 know, are merely electrolytic conductors of very high resistance and 

 the values of their Specific Inductive Capacity may be regarded as 

 indicating their relative conductivities : if, as argued above, the 

 passage of electricity through gases be dependent on the formation of 

 complex conducting systems comparable with those which there is 

 reason to believe condition the conductivity of liquid electrolytes, 

 the probability that vacua such as Sir James Dewar has obtained 

 would afford results different from those previously obtained is con- 

 siderable : in any case it is desirable to examine into their behaviour. 

 The whole subject is in need of further investigation, not in any dog- 

 matic spirit but rather in that which Faraday had in mind when 

 recommending the science of electricity as a fine and ready field of 

 discovery — "to those philosophers who pursue the inquiry zealously 

 yet cautiously, combining experiment with analogy, suspicious of their 

 preconceived notions, paying more respect to a fact than a theory, not 

 too hasty to generalise and, above all things, willing at every step to 

 cross-examine their own opinions both by reasoning and experiment." 



Although of late years electrical considerations have been intro- 

 duced into chemical discussions, this has been done in so narrow a 

 spirit that the security of our position is but little greater than when 

 the connexion was first established by Faraday himself in his earhest 

 researches. 



The refined and laborious determinations previously made (1895- 

 97) in the Royal Institution Laboratory of the dielectric constants of 

 various liquids and frozen electrolytes at the low temperatures afforded 



