224 THE NEW QUANTUM THEORY 



quanta to outline the diffraction image; our one scattered 

 quantum can only stimulate one atom in the retina of 

 the eye, at some haphazard point within the theoretical 

 diffraction image. Thus there will be an uncertainty in 

 our determination of position of the electron propor- 

 tional to the size of the diffraction image. We are in a 

 dilemma. We can improve the determination of the 

 position with the microscope by using light of shorter 

 wave-length, but that gives the electron a greater kick 

 and spoils the subsequent determination of momentum. 



A picturesque illustration of the same dilemma is 

 afforded if we imagine ourselves trying to see one of the 

 electrons in an atom. For such finicking work it is no 

 use employing ordinary light to see with; it is far too 

 gross, its wave-length being greater than the whole 

 atom. We must use fine-grained illumination and train 

 our eyes to see with radiation of short wave-length — 

 with X-rays in fact. It is well to remember that X-rays 

 have a rather disastrous effect on atoms, so we had better 

 use them sparingly. The least amount we can use is one 

 quantum. Now, if we are ready, will you watch, whilst 

 I flash one quantum of X-rays on to the atom? I may 

 not hit the electron the first time; in that case, of course, 

 you will not see it. Try again; this time my quantum 

 has hit the electron. Look sharp, and notice where it is. 

 Isn't it there? Bother! I must have blown the electron 

 out of the atom. 



This is not a casual difficulty; it is a cunningly 

 arranged plot — a plot to prevent you from seeing 

 something that does not exist, viz. the locality of the 

 electron within the atom. If I use longer waves which 

 do no harm, they will not define the electron sharply 

 enough for you to see where it is. In shortening the wave- 

 length, just as the light becomes fine enough its quan- 



