FRIEDRICH HASENOHRL 375 



of the continual transformation of energy, and this would 

 contradict our experience in mechanics. The masses of 

 energy entering into ordinary processes are however very 

 small; for the square of the velocity of light which enters 

 into their calculation in the denominator is a very large 

 quantity. Nevertheless, the sun, for example, loses energy 

 in the form of its radiation to the extent of five million tons 

 of mass per second, of which about two kilograms fall on the 

 earth, and these suffice to accomplish all known effects of 

 energy (with the exception of volcanic energy and that of the 

 tide). 



If we assume Hasenohrl's result to hold for all forms of 

 energy, it is the more remarkable, since energy now appears 

 exactly like a substance; it is not only invariable in its quan- 

 tity, as Robert Mayer had already shown, but it also pos- 

 sesses mass. With or without this generalisation to cover 

 all forms of energy, Hasenohrl's result was as well founded 

 as any new form of natural knowledge can be; it needs con- 

 tinual further proof in its application, until it is rendered 

 sufficiently secure, and the limits of its validity are known. 

 The applications of this idea have already progressed very 

 far to-day, although almost entirely in the names of other 

 people - but nowhere has any contradiction with experience 

 been found, but on the contrary continual confirmation. 

 Indeed, Hasenohrl's result could be further extended to 

 show that, associated with the mass of energy, there is a cor- 

 responding weight, so that energy is subject to gravitation 

 like all masses, and further even, that the masses of tangible 

 and material bodies are to be regarded only as energy masses, 

 and the weights of these bodies as the weights of the energy 

 they contain. 



In this connection we may make the following further 

 remarks. 



A confirmation of the result was obtained by swift cathode 

 rays. If we regard kinetic energy as likewise possessing 



