438 Proceedings of Royal Society of Edinburgh. [sess. 
in mind that no account has been taken of the energy lost by the 
Rontgen radiation in passing through the walls of the Rontgen 
lamp, and that a particular coefficient of transformation of energy 
into luminescence has been assumed. It is evident, however, from 
the results obtained, that the true average power of the Rontgen 
rays, i.e ., their energy divided by their duration as such, is much 
greater than generally supposed, and that about ten gram- calories 
per second may be taken as a lower limit to its magnitude. 
To Professor E. Wiedemann and his assistant Dr E. Muller my 
best thanks are due for the help they so kindly gave me in carry- 
ing out this investigation. 
