264 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



significance in the scale of the cosmos. We can only briefly sketch 

 some of the suggestions that have been made in this connection. 



First, we could view the planets or other cosmic bodies as electrically 

 charged to very high potentials, so that charged particles coming to 

 them from space could acquire great energies in reaching them. It 

 is with some comfort that one finds a fairly general method of dis- 

 missing this naive suggestion. While interstellar space contains 

 only about one atom per cubic centimeter, there is reason to think 

 that it is a comparatively good conductor of electricity for small 

 electric fields. A large portion of interstellar atoms is ionized by 

 ultraviolet starlight, and the mean free path of the ions is large 

 because of the low density. Therefore, on a simple view of the matter, 

 the electrical conductivity of interstellar space should be comparable 

 with that of a completely ionized gas at atmospheric pressure and 

 should amount, in fact, to two percent of the conductivity of copper. 

 Under such conditions, any electrostatically charged body in the 

 galaxy would become rapidly discharged. 



A rotating, magnetized, conducting sphere experiences electro- 

 dynamic forces resulting from the rotation of its substance in its 

 own magnetic field. Such a rotating sphere develops a potential 

 difference between its axis and its equator. A star the size of our 

 sun, possessing a magnetic field like that attributed to the sun until 

 recently, would acquire a potential difference of about three billion 

 electron volts when rotating in a nonconducting medium. For a 

 magnetic star, such as was cited by H. W. Babcock, with a field of 

 some 6,000 gauss at the pole and twice the sun's radius, the potential 

 difference would be of the order of a thousand billion volts for the 

 same angular velocity. 



These potential differences would not be completely annulled by the 

 electrical conductivity of interstellar space since they would be con- 

 tinually rejuvenated by the rotation of the star. They would be modi- 

 fied depending upon the ratio of the conductivity of space to the con- 

 ductivity of the star itself. Under suitable conditions, such a rotat- 

 ing star could shoot out from one of its poles charged particles which 

 at great distances would show cosmic-ray energies. 



Recognizing the existence of violent magnetic disturbances on 

 stars, akin to the growth of sunspots with their accompanying mag- 

 netic fields, the writer, some 20 years ago, suggested that such phe- 

 nomena might result in cosmic-ray energies. The mechanism is quite 

 analogous to that of an ordinary electrical transformer, where we 

 have a changing magnetic field threading through a wire circuit and 

 inducing therein an electromotive force which drives the current 

 through the circuit. The actual circuit itself is not necessary for the 

 realization of the electromotive forces, and if there be charged par- 



