390 THIRD REPORT — 1833. 



to vary between them according to the general law already 



arrived at. It varies also as — -, ^r^, that is, inversely as the 



a . {a + 2r) •' 



distance between the nearest points multiplied into the distance 

 between the centres. 



The author found these deductions accord very completely 

 with subsequent experiments, so that the weight requisite to 

 counterpoise the force between two equal spheres at given di- 

 stances may be invariably predicted with great precision. Some 

 of these results were exhibited to the Section by means of the 

 balance. 



When two plane circular areas, each equal to the areas of the 

 hemispheres rectified into plane surfaces, are opposed to each 

 other, and placed so as to pass through the points q q' above 

 mentioned, the attractive force is extremely near that obtained 

 by means of the opposed spheres, the distances being estimated 

 from the same points. 



The author beHeves that many of the results thus arrived at 

 have not been hitherto included in the received theories of elec- 

 tricity, and is disposed to think that we may yet arrive at easier 

 views of electrical action, and hence bring the phaenomena more 

 completely under the dominion of analysis. 



On Electricity/. By the Rev. John G. MacVicar, of St. 

 Andrew s. {Extract of a Letter from the Author to the Rev. 

 W. Whewell, F.R.S., &c.) 



As a basis for his theory of electrical phaenomena, Mr. Mac- 

 Vicar assumes that those parts of bodies which are capable of 

 displaying electric phsenomena possess a filamentax'y or acicu- 

 lar stiucture, an hypothesis which he is not disposed to rest 

 upon such a consideration as M. Ampere makes it rest, when 

 advancing his hypothesis of magnetic action, (namely, that by 

 making such a supposition one may explain many phaenomena,) 

 but upon these two principles : First, The action of the first law 

 of motion, which nnist ever tend to distribute the matter in 

 which impulses are embodied in a filamentary or acicular ar- 

 rangement, or at all events in an arrangement in which a linear 

 continuity of matter is maintained, which (since every material 

 medium is known to be very porous,) can only give rise to such 

 a structure. Secondly, Upon the known intimate structure of 

 bodies, so far as that can be observed by the microscope, du- 

 ring solidification, by cleavage or otherwise. 



This granted, he inquires what ai-e the pheenomena of trans- 

 verse vibration that must be displayed by such filamentary 



