Ofi Ncwloii's llings and the Fixed Lines of the Spectrum. 183 



N.B. Should it be in your power to procure me any ob- 

 servations made of this eclipse in England or America, you 

 would greatly oblige thereby 



Your obedient Servant, 



Hamburg, Oct. 5, 1836. C. RuMKER. 



XL. A simple Mode of exhibiting Newtoji^s Bings, and a 

 Mode of exhibiting the Fixed Lines in the Spectrum, By 

 the Rev. W. Ritchie, LL,D.,RR.S., Professor of Natural 

 Philosophy in University College^ and in the Royal Institu- 

 tion of Great Britain,* 



1. T^O exhibit Newton's rings a lens of a long focal di- 

 -*- stance is generally considered necessary, which is both 

 expensive and difficult to obtain. In a lecture which I de- 

 livered nearly two years ago in the Royal Institution, 1 showed 

 a very simple mode of performing the experiment, which, I 

 have no doubt, will be acceptable to many of your readers. 

 Take two circular pieces of thin plate glass (Dutch plate) 

 about six or eight inches diameter. 



Gild a ring of one of the plates about a quarter of an inch 

 broad from the circumference of the circle with gold-leaf, 

 place the plates over each other, and by means of a rectan- 

 gular frame of iron or brass and a screw, bring the plates to 

 touch in the centre. Let a b 

 represent the glass plates, B C 

 the rectangular frame, S a 

 screw, and A a projecting point, b 



By means of the screw the 

 plates will be brought to touch 

 in the middle, whilst they are 

 separated at the circumference 



by a single gold-leaf. When this is held so that light from 

 the sky or a lamp falls obliquely on the plates so as to be re- 

 flected by the under plate to the eye, the rings will present 

 themselves in circles round the dark spot in the centre. 



2. Procure a prism of good flint glass, having one of its 

 angles containing 70 or 80 degrees. Place two thin slips of 

 metal with smooth edges in an opening in a window-shutter, 

 through which the white light of the clouds is admitted. View 

 i\{\sfilm of light through the large angle of the prism kept 

 close to the eye, and the principal fixed lines as well as many 

 of the others will be distinctly visible. If a bottle containing 

 nitrous gas be placed opposite the opening, the lines will be- 

 come more strongly marked and more numerous. With one 



* Communicated by the Author. 



s 



