TRANSACTIONS OF SECTION A. 



587 



a known current is flowing. For this purpose the same balance mentioned above 

 is used. 



A few of the numerous determinations of the susceptibility coefHcients are 

 given below. The middle column gives the field strengths at which the determi- 

 nations are made. 



Substance. 

 Italian marble 

 Optical glass 

 White wax 

 "White wood . 

 Sulphur . 



H 



8,080 

 8,120 

 8,220 

 .3,700 

 8,220 



- -945 X 10-" 



- -578 X 10-^ 



- -560 X 10-« 

 -•176x10-5 

 -•765xl0-fi 



The question as to whether the coefficient k is constant when the field strength 

 H is varied is discussed. The following determinations were made upon bismuth. 



Substance. 

 Bismuth 

 Bismuth 

 Bismuth 

 Bismuth 

 Bismuth 



H 



1,640 



3,680 



8,220 



8,830 



10,490 



>- 12-55 X 10-« 

 -12-22x10-5 

 -12-27 xlO-« 

 -12-50x10-^ 

 -12-34x10-" 



11. On Magnetic Periodicity as connected tvith Solar Physics. 

 By Arthur Harvey. 



The author advances as a connected theory of solar physics that the sun's 

 true body is within the envelope of which we see the surface ; that it rotates more 

 slowly than the luminous (photospheric) cloud-layer, from the spots on which the 

 sun's rotation has been calculated ; that spots and prominences are symptoms of 

 disturbances which have their seats on the inner sun ; that these loci of intense 

 chemical action occupy large areas, and are intermittent and recurrent in their 

 activity. 



He reviews the arguments respecting periodicity in the cases of sun spots and 

 of waves of heat and cold, and seeks to establish, from the records of magnetic 

 observations at Toronto, beginning in 1841, that there is a periodicity in magnetic 

 disturbances of 27-24575 days, which the author thinks is the synodical rotation 

 period of the true body of the sun, with which the recurrences of sun spots, of 

 solar protuberances, of hot and cold waves upon the earth, and other phenomena 

 dependent on solar action must harmonise. 



From thermal considerations Mr. Carlos Honors, of Montevideo, arrives at a 

 result almost identical with that of this paper. 



WEDNESDAY, AUGUST 25. 



The following Papers were read : — • 



1. On the Refractivity of Certain Mixtures of Gases. By Professor 

 Ramsay, F.R.S., a?icZ Morris W. Travers. 



The authors found that the refractivity of air being taken as unity, that of 



Oxj'gen was .... 0-9243 



Nitrogen 

 Argon 

 Hydrogen 

 Helium 



1-0163 

 0-9596 

 0-4733 

 0-1255 



They imestigated the ratio of the refractivities of oxygen, nitrogen, and argon, 

 and compared them with that of air. It was found that the sum of the refrac- 



