TRANSACTIONS OF SECTION A. 609 



3. Interim Report on Cosmic Dust. 



4. Report on Underground Temperature. — See Reports, p. 75. 



5. Report on the Sizes of the Pages o/ Periodicals. — See Reports, p. 77. 



6. Report on the Comparison and Redtiction of Magnetic Observation, 



See Reports, p. 209. 



7. Interim Report on the Comparison of Magnetic Standards. 

 See Reports, p. 79. 



FRIDAY, SEPTEMBER 13. 



A joint Meeting with Section B. 



The following Papers were read : — 



1. The Refraction and Viscosity of Argon and Helium. 

 By Lord Rayleigh, Sec. R.S. 



As compared with dry air, the refraction (/x — 1) of argon is 0'961, and that of 

 helium (prepared hy Professor Ramsay) is as low as 0'146. 



Dry air being again taken as the standard, the viscosity of argon is 1-21, and 

 that of helium is 0'96. 



2. On Specific Refraction and the Periodic Law, tvith reference to Argon 

 and other Elements. By Dr. J. H. Gladstone, F.R.S. 



In 1869, 1877, and 1883 the author had shown that the specific refractive 

 energies of tlie metallic elements are usually in the inverse order of their combinino- 

 proportions, and that the specific refractive energies of the elements in general are 

 to a certain extent a periodic function of their atomic weights. 



The present communication refers to some developments of these old obser- 

 vations. 



(1) Argon. The specific refractive energy of argon gas, as reckoned from Lord 

 Rayleigh 's data, is 0-159. Deeley had suggested that this property might throw 

 light upon the question whether the atomic weight is about 20 or double that 

 figure. The following are the specific refractive energies of the elements with 

 atomic weights between 12 and 23, with the insertion of argon. Carbon, 0-417 • 

 nitrogen, 0-236; oxygen, 0-194; fluorine, 003 (?) ; argon, 0-159; sodium, 0-209^ 

 Argon appears to be here in place on the rise which follows the great descent from 

 carbon to fluorine. It does not equally well fit the neighbourhood of calcium, 0-250. 

 If the atomic weight be 19-94, the molecular refraction will be 315, which is 

 almost the same number as that for oxygen gas, 310, or nitrogen gas, 3-30. 



(2) The fact that the specific refractive energies of the univalent metals are 

 generally inversely as the square roots of their atomic weights is conflrmed by 

 farther research, the product of the two being about 1-3. The same observation is 

 now extended to the earthy metals i i the second column of Mendel(5eft"s table the 

 products in that case being fully 1-4. The rule does not apply to the halogens in 

 column 7. As to column 8, iron, palladium, platinum, and gold all give products 



1895. R R 



