PROCEEDINGS: PHIIvOSOPHICAL SOCIETY 269 



confocal to the given homoeoid and passing through x, y, z; the intensity 

 is along the normal and directed inward, or towards the given shell. 



On the basis of equation (i) and MacLaurin's theorem the author 

 has deduced: 



1. Expressions for the field of an inductively magnetized rotation 

 ellipsoid in a more convenient form for the general case than previous 

 ones. 



2. Expressions for the field of an inductively magnetized prolate 

 elliptic homoeoid have been established, possibly for the first time. 



It was also shown that expressions in finite form may be established 

 for the field of an inductively magnetized elUptic homoeoid in general — 

 that it is not necessary to assume a rotation elliptic homoeoid. This 

 matter is of special interest in view of the fact that expressions for the 

 field of an inductively magnetized soUd elUpsoid, in general, have not 

 yet been estabHshed in finite form. 



In conclusion various applications of the derived formulae were given. 



The paper was illustrated by lantern slides and was discussed by 

 Messrs. Abbot, Littlehales, Sosman and Humphreys. 



The second paper, also illustrated by lantern slides, was presented by 

 Mr. S. J. Mauchly on Some results of atmospheric-electric observations 

 made during the solar eclipse of June 8, igi8. • 



The observations forming the subject of this paper were made in the 

 belt of totality near Lakin, Kansas, in accordance with the general 

 plan of the Department of Terrestrial Magnetism of the Carnegie In- 

 stitution of Washington for magnetic and electrical observations 

 during the total solar echpse of June 8, 1918. The observing station 

 was located on a level treeless plain and the general weather conditions 

 on the afternoon of the echpse were favorable for atmospheric-electric 

 observations. The period of totality at Lakin was of about 84 seconds 

 duration. 



The potential-gradient was determined from eye readings of an elec- 

 troscope giving the p. d. between the earth and an ionium collector 

 supported at a distance of 95 cm. above the ground, from the middle of 

 a long, insulated, horizontal wire. Observations were made every 

 two minutes over a period of 6 hours approximately symmetrical about 

 the time of totality. The main results may be summarized as follows : 



(i) Beginning 8 minutes before and continuing througl;out totality 

 there was a rapid but nearly uniform decrease of the potential-gradient 

 amounting to about 25 per cent of the values immediately preceding. 

 The general minimum thus established persisted for about 20 minutes 

 after totality and was marked by a sharp secondary minimum 6 

 minutes after mid-totality. 



(2) Throughout the general minimum referred to there was almost 

 total absence of the irregular, short-period, fluctuations which char- 

 acterized the potential-gradient on the afternoon of the eclipse. Be- 

 ginning 20 minutes after totahty and continuing for about 20 minutes 

 there was a marked but gradual increase to approximately normal 



