524 
IIOX. E. J. STRUTT OX THE COXDUCTIYITY 
It is certain, therefore, that the relative conductivity of gases under the penetrating 
type of Becquerel rays are mainly, tliough not wholly, dependent on their densities. 
This result is of considerable interest; the investigations of Becquerel, Giesel, 
and others have made it clear that rays of this type resemble the cathode rays in 
many respects. Both are deflected Ijy a magnetic and by an electrostatic field ; and 
carry an electric charge. Here we have one more property in common. For the 
experiment of Ma.cLenxan, quoted in tlie table, established the conclusion that the 
Diagram Xo. 6. 
cathode rays too produce a condiictivity in gases ])roportional to the density. There 
is not, however, the same departure from the law in the case of hydrogen. Under 
cathode rays the conductivity of hydrogen relative to the other gases is exactly what 
the law of density would recpiire. 
So much for the rays deflected l)y a magnet. We have still to consider the rays 
which are not deflectable. 
well obeyed by the other gases, that there is large and unexplained discrepancy between the values 
found for the relative conductivity of hydrogen under Ebntgen rays liy J. J. Thojisox and Perrix 
respectively, although their determinations agree fairly well in most other cases, 
