FRIEDRICH HASENOHRL 379 



and disintegrate in the process; otherwise all atoms are able 

 to take up energy from their surroundings, and to give it up 

 again, and as we have found, they do this by quanta. We 

 have likewise already remarked that all energy existing out- 

 side the atoms (electro-magnetic waves and all electro- 

 magnetic fields of force) is only derived from atoms. As 

 distinctive of matter there remains the positive elementary 

 quantity of electricity, which appears to be a fundamental 

 constituent of all atoms, inasmuch as none of these positive 

 quantities, as distinguished from the negative charges, the 

 electrons, can be removed from an atom without destroying 

 the same, and transforming it into another kind of atom. 

 The positive quantity also carries a very much larger mass - 

 that is to say energy - than the negative, a mass over one 

 thousand times as great, if the lightest atom, that of hydro- 

 gen, consists of only one positive and one negative elementary 

 charge, as would appear from our present knowledge. 



If we cast our eyes over the discoveries made concerning 

 ether from Huygens to Hasenohrl, we still notice that our 

 knowledge is very incomplete. Originally, in Huygens' 

 case, the ether appeared as the medium in which the waves 

 of light are propagated, the knowledge of which was very 

 greatly extended by Young, Fraunhofer and Fresnel. Then, 

 thanks to Faraday, Maxwell, and Hertz it was generally 

 recognised as the medium of all electro-magnetic forces, 

 which are also the essential feature of light-waves. Later 

 on, the interference experiment continually refined since 

 the time of Fresnel,^ together with observations of double 

 stars, showed that the ether cannot be assumed to be either 

 stationary or in motion in the whole of cosmic space, but 



1 We refer particularly to the Michelson experiments; but other electro- 

 magnetic experiments belong in the same category, and these have often 

 been summarised, and will be found specially tieated in my At her und 

 Urdther. A further interference experiment, which has hitherto been 

 far too little followed up, appears to show that the ether does not take 

 part in rotary motions of matter. The beginning of all these experiments 

 goes back to Maxwell (see Nature, 29th January, 1880, page 314 ff.)- 



