Discontinuity in the Phenomena of Radiation 59 



bridge the gap that separates the early Hertzian waves from the 

 long infra-red waves and have so far succeeded as to reach a 

 wave-length of 6 mms. The accompanying slide* will give you 

 some idea of radiations which have actually been detected and 

 measured by the variety of means at our disposal, except that 

 the dark portion indicating the gap between infra-red and 

 electrical should be actually smaller owing to work carried out 

 since this diagram was constructed. Further, a remarkable 

 series of researches carried out since 1912 have suddenly opened 

 up a new field of knowledge at the other extreme of the complete 

 radiation range. This refers to the nature of the X-rays. It 

 had long been suspected that they were ethereal vibrations with 

 the same elements of undulatory motion in them as in ordinary 

 light waves ; it was also known that if this view as to their 

 nature were correct, their wave-lengths must be very short 

 compared even with the 60 millimicrons or -06 micron of the 

 extreme ultra-violet so far attained. This inference has been 

 fully justified. Taking up an observation, first announced by 

 Professor Laue of Zurich, Professor Bragg of London and his 

 son, together with the late Henry Moseley of Manchester 

 University, published a series of researches opening up a new 

 avenue of knowledge whose possibilities we are just beginning to 

 realize. Sufficient to say, that they have demonstrated beyond 

 doubt the ethereal nature of the X-rays. From the heterogeneous 

 stream of X-ray radiation emitted by any bulb, it is possible to 

 isolate and measure the wave-lengths of individual, almost 

 homegeneous, streams. It is possible also, by varying the metal 

 of the anticathode and by using a high enough voltage, to make 

 a bulb emit practically nothing but an extremely homogeneous 

 radiation, characteristic of the particular metal used and closely 

 analogous to the kind of radiation emitted, say, by incandescent 

 sodium except for the much shorter wave-length. The natural 

 unit of length for these waves turns out to be the millimicron, or 

 even -1 of it, the so-called Angstrom unit. Thus, for instance, 

 * Fig. 3. 



