88 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



former only in the immediate vicinity of the value of H which conforms 

 to equation (3) ; for the protons are turned over only when the Larmor 

 frequency agrees very nearly with the applied frequency. Accordingly 

 one keeps the alternating field on all the time and plots a single curve; 

 and this is marked by a fine sharp peak, but this time a peak that points 

 downward, Fig. 6, for it testifies to the absence of the overturned protons 

 that have missed the detector. 



The first experiment of this kind was done on molecules of lithium 

 chloride. The reader may have been puzzled that I spoke of a beam of 

 molecules and then of the deflection of protons: the protons, or whatever 

 other magnetic nuclei are being studied, carry the molecules with them. 

 In the experiments on LiCl, the peaks of lithium and of chlorine were 

 found in different parts of the curve. Later the proton-resonance was 

 discovered by using molecules of KOH and NaOH, and confirmed with 

 molecules of H2 and HD (the latter being a hydrogen molecule of which 

 one nucleus is a proton and the other a deuteron). It is from this molecule 

 of HD that the proton-resonance, and for that matter the deuteron- 

 resonance also, stand out most clearly and sharply. In H2 and in D2 

 the resonances are perturbed and multiplied, but for reasons which are 

 well understood so that the theory is strengthened instead of being 

 weakened; but to describe these pretty things would be confusing 

 unless they were explained, and to explain them would take us far 

 afield. 



SOME APPLICATIONS OF NUCLEAR MAGNETIC RESONANCE 



The first of the uses of nuclear magnetic resonance is of interest 

 mainly to the nuclear theorist. He wants to know (//m) for as many 

 nuclei as possible; and this knowledge may be found by locating the 

 resonance-peaks, and applying to their values of H and p the equation 

 (3) or (5) which I repeat: 



H = il/fi)hp (9) 



Anyone who is going to burrow into the literature of this subject 

 must be apprised beforehand, or else find out the hard way, that this 

 simple statement is variously expressed. Here is a sad case of the 

 ruination of a beautiful terminology by carelessness. The terms which 

 have been mined are "gyromagnetic ratio" and "magneto-mechanical 

 ratio." The former ought to mean, as originally it did mean, the ratio of 

 angular momentum to magnetic moment. The latter ought to mean 

 the ratio of magnetic moment to angular momentum. Both have by 



