230 Intelligence and Miscellaneous Articles. 



the upper ones contain pelagic shells. Dykes of augite and hyper- 

 thene-andesite project on the shore, and a representative of' the 

 plutonic series occurs. There is evidence that the island has been 

 elevated and again submerged prior to the elevation which has raised 

 it to the present height. The volcanic basis is largely invested with 

 limestone, and this rock forms the summit 1078 feet above sea-level. 

 Sections show that it is a shallow-water deposit. 



Of the purely limestone structures, Tongatabu, Nomuka, and the 

 long reef on which the larger islands of the Hapaii group are 

 situated form more or less complete atolls, all of which have been 

 elevated to a greater or less extent. 



The Vavau group is remarkable for its very indented contour, 

 suggesting the idea that it rests on a much denuded basis. Both 

 here and at Eua there are raised limestone formations with atoll or 

 barrier-like contours ; and there is some direct evidence to show 

 that these have been formed without the aid of subsidence. 



The presence of islands formed of volcanic materials laid out in 

 layers beneath the sea, and the manner in which the recently formed 

 Falcon Island is now being reduced to the condition of a submarine 

 bank, suggest that the atolls of the group may rest on similarly 

 formed foundations. 



4. " On the Inverness Earthquakes of November 15th to De- 

 cember 14th, 1890." By C. Davison, Esq., M.A. 



In this paper the author gives reasons for supposing that the 

 Inverness earthquakes of last year were due to the subsidence of a 

 great wedge of rock included between a main fault and a branch 

 one ; and he considers that there is little doubt that these recent 

 earthquakes were the transitory records of changes that, by almost 

 indefinite repetition in long past times, have resulted in the great 

 Highland faults. 



XXXII. Intelligence and Miscellaneous Articles. 



ON THE DETERMINATION OF THE DIELECTRIC CONSTANT OF 

 GLASS BY AID OF VERY RAPID ELECTRICAL OSCILLATIONS. 

 BY R. BLONDLOT. 



YEB.Y rapid electrical oscillations, such as areproduced by Hertz's 

 apparatus, have been utilized by Prof. J. J. Thomson for the 

 measurement of the dielectric constant*. Prof. Thomson draws from 

 his experiments the following conclusion: " for vibrations whose 

 frequency is ... . 25,000,000 per second, the specific inductive 

 capacity [of glass] is very nearly equal to the square of the refrac- 

 tive index, and is very much less than the value for slow rates of 

 reversals." 



As regards this conclusion we might demur to the use of the 



* J. J. Thomson, " Specific Inductive Capacity of Dielectrics when 

 acted on by very rapidly alternating Electric Forces," Proc. Roy. Soc. 

 June 20, 1889. 



