Gudzin, M.G. <br/><br/>
Seismological observatories / by M. G. Gudzin and E.G. Hull-e. 

 - Estados Unidos : IRE 
 - 10 p. 
<br/><br/> "Reprinted from the Proceedings of the IRE, Vol.50,No.11,no-vember, 1962".