486 Mr. Laming on the primary Forces of Electricity. 



nii3sing the principle of the photometer, for he has considered 

 the magnitude of the reflecting surface as a fundamental 

 datum in determining the brightness of the image perceived 

 by the eye. 



In concluding, I must be allowed to observe, that the ex- 

 perimental part of my photometrical investigations on the re- 

 lative intensity of the light in Newton's rings seen by trans- 

 mission, and on the reflective powers of diamond and glass 

 of antimony, having been confirmed by Mr. Wheeler's ex- 

 periments, the calculated results press upon our attention 

 ^ith full force, the inadequacy of the undulatory theory of 

 light, of which the results predicted are palpably at variance 

 with the fact. 



Cambridge, April 18, 1838. 



LXXVI. On the 'primary Forces of Electricity, By Richard 

 Laming, Esq., MM.CS* 



1. 'T^HE experiments of Coulomb, and the more recent and 

 -*- beautiful manipulations of Mr. Harris, have completely 

 established the fact, that in our atmosphere bodies dissimilarly 

 electrified, attract one another with a force which varies in- 

 versely as the square of the distance. That the same ratio 

 obtains in an ordinary vacuum might now be theoretically 

 deduced from the results of experiments on the discharging 

 distances of different electrical accumulations through air of 

 various densities ; but as the fact is of fundamental importance, 

 I have thought it worth while to attempt its induction by 

 more direct experiments. 



2. Li order conveniently to estimate the attractions of such 

 minute quantities of electricity as are susceptible of being re- 

 tained by a conductor placed in highly rarefied air, it became 

 necessary to construct an electrometer that should be very 

 delicate, and at the same time occupy but litde space. Ac- 

 cordingly an elliptical beam If inches in length, made of a thin 

 lamina of gilded mica, was supported as a balance on two fine 

 needle points; a circular plate 1| inches in diameter, of the 

 same material, was suspended by silver threads to one of the 

 arms of the balance, and counterpoised by a weight attached 

 by sliding straws to the opposite arm. The index, 2| inches 

 in length, consisted of a needle of glass, carrying at its upper 

 end a plate of mica, by means of which the scale could be 

 read off* without error from parallax. Two short straws, one 

 sliding with friction within the other, were so adjusted under 



• Communicated by the xiulhor. 



I 



