﻿On the Corona seen in Total Eclipses of the Sun. 225 



may always be traversed by sparks ; part of the originally excited 

 electricity is thereby neutralized, and we have the original case. 

 Hence it is that for each electrophorus there is a maximum 

 action, depending on the condition of the air, which cannot be 

 exceeded by any rubbing, be it ever so strong. All this may 

 indeed be deduced from the known fundamental principles of 

 electricity; it nevertheless seemed desirable to confirm this by a 

 special experiment. 



From the experiments here adduced it follows that all pheno- 

 mena observed on the electrophorus may be explained by action 

 at a distance, and that it is unnecessary to have recourse to 

 the assumption of an inductive action in the insulator. All 

 these explanations may readily be put into a mathematical 

 form. This will be done in the more complete paper, in which 

 much of the experimental detail will be discussed. Here I was 

 only concerned to produce in their connexion the most essential 

 experiments, and to give their explanation in general outline. 



Briefly summed up, we may say that the process in the ordi- 

 nary mode of using the electrophorus is as follows : — 



The electricity produced by rubbing the upper surface of the 

 cake acts inductively upon the form. 



If the original excitation is strong enough, the (opposite) elec- 

 tricity of the form traverses the space between the latter and the 

 cake, and passes to it, forming spark discharges. 



Both by this electricity which has passed, and by the residual 

 electricity in the form, the primarily excited of the upper surface of 

 the cake is partially bound. 



The force which is operative in the space between the subsequently 

 superimposed cover and the cake is by this diminished, and an ex- 

 change of electricity in this space is prevented. 



The electricity of the opposite kind produced in the cover by the 

 induction of that primarily excited remains upon it, and by con- 

 ducting off electricity of the same kind and raising the cover becomes 

 free — that is to say, is made electroscopically active. 



All other accompanying phenomena may be explained from these 

 points of view according to known laws. 



XXIX. On the Corona seen in Total Eclipses of the Sun. 

 By Professor W. A. Norton*. 



IN a former communication f I alluded briefly to the auroral 

 theory of the solar corona, and referred to publications in 

 which I had advocated it. I propose now to give a brief 

 discussion of the theory. 



* From Silliman's American Journal for January 1871. 

 t Silliman's Journal for September 1870. 



Phil. Mag. S. 4. Vol, 41. No. 272. March 1871. Q 



