On the Iiifexhn, RifexLii, and Colour] of Lij^ht. 557 



unlefs the fucceffion continued through all the images, the outermofl of all was red, and 

 the innermoft image had univerfally violet in the infidc. 



Obf. IV I placed at a hole in the window fhut a prifm to refracl the r.iys, and received 

 the fpedrum at the diftance of fix feet from the window on a chart ; then at the diflance 

 of two feet I placed a fcreen vrith a hole in the middle of it, through which I let pafs fuc- 

 ceffively the different rays. At the diftance of one inch from the hole, between it and the 

 chart, I placed the reflefting cylindrical body ; the images were found on the chart and 

 Avails of the room round to the fides of the hole on the fcreen, and were always wholly 

 of the colour in which they were formed, except in the confines of the green, where a 

 fmall quantity of white light fell, and made them of all the feven colours ; but this \vas 

 almoft wholly prevented by ufing a prifm with a greater refrading angle, and holding the pin 

 and fcreen farther from it. I then removed the fcreen, and left the refleftor in its place, fo 

 as It might reach through the rays; and thus there were formed images having in them, 

 from top to bottom, the feven colours, one after another, the loweft divifion being red, the 

 higheft violet. They were inclined confiderably towards their tops, and were much, 

 broader at the bottom or red parts than at the tops or violet parts. And laftly, the 

 rencaor being moved fo that the images might be difturbed (as in tlie former experiment 

 made in the white light}, the red was moft, the violet leaft dilated. In cafe thefe eftefts 

 might be owing to any peculiarities in the fliape orpofition of the refleaor, I placed at three 

 feet from the prifm a lens of four inches breadth, to colled the rays to a focus, fix feet be- 

 yond which 1 held a chart, and there received the fpedrum inverted, the red being upper- 

 moft, and the violet undermoft ; holding the refledor at two feet from the focus and four 

 from the chart, the images were formed juft as before, only inverted, inclining towards the 

 violet, of greater breadth towards the red, and more diftended towards the fame quartet 

 wlien the refledor was moved. 



Obf. V. Things remaining as in the lad part of the laft Experiment; at the focus of the 

 lens I placed a fecond prifm, which refraded the rays into a white beam *, and this I re- 

 ceived on a fcreen with a hole in the middle, through which a fmall part of it pafled, and 

 falling on the rcfledor placed behind was formed by it into images after the manner of the 

 firft Experiment, each having in regular order tlie feven prifmatic colours. One of the 

 brightcft and moft diftind I let pafs through a hole in the fecond fcreen, and it fell on the 

 chart. I then caufed an afliftant to intercept the red rays between the firft prifm and the 

 lens, and immediately the red part-of the image vaniftied ; and when the violet was inter- 

 cepted, the violet of the image vaniftied ; and if the green was intercepted, tlie green was 

 wanting in the image. In ftiort, whatever colours were ftopped, the fame were miffing 

 in the image. In Fig. 6. the rays paBing through the hole C of the window, A B are re- 

 fraded by the prifm P M N, and feparated into D V, D G, and D R, violet, green and red ; 

 which, being coUeded into a focus F by the lens L, are there agaifi refraded by a prifm 

 P' M'N', and formed into a whitetscam a b m n, part of which is intercepted by the fcreen 

 S S', and part paftes through the hole h, as h H to H on the cliart X Y Z W, and part is 

 rededed by the body oq into a fet of images which are received on a fcreen T U, and one 

 of them, r g v, let pafs to W X Y Z ; but when an obftacle E ftops D R, r the red va- 



• Optics, Book ii. P.irt il. Prop, i 



niflies ; 



