230 PHILOSOPHICAL TRANSACTIONS. [aNNO I716. 



and thereupon reported that the experiment did not succeed, And lately the 

 editor of the Acta Eruditorum for October 1713, p. 447, desired that Sir 

 Isaac Newton would remove this difficulty. " The objections, says the editor, 

 made by learned men, both in France and England, against the theory of 

 colours, were happily answered by the sagacious Mr. Newton, as is abundantly 

 evident from the Philosophical Transactions, N° 84, 85, 88, 96, 97, 121, 123, 

 128; whence many wish he would please to give his sentiments on the difficulty 

 started against that theory by the late ingenious M. Mariotte, who Was both an 

 indefatigable and successful inquirer into nature, in his treatise of colours, p. 

 207, et seq. At the distance of about 25 or 30 feet, he received on a paper, 

 a ray admitted through a small hole into a dark room, and transmitted through 

 a triangular prism; then he received with another prism in a very oblique posi- 

 tion the violet colour, possessing a space upwards of three lines, and trajected 

 through a slit of two lines; on which he observed, that some part of it was 

 changed into a red and yellow colour; and in like manner he found, that a part 

 of the red light was changed into a blue and violet colour. Now on admitting 

 this transmutation, it is manifest, from the Acta Erudit. for 1706, p. 60, et 

 seq. that Sir Isaac Newton's theory falls to the ground; M. Mariotte took the 

 distance of 30 feet, lest any should object, that by taking a less distance, the 

 heterogeneous rays had not been perfectly separated ; but to me M. Mariotte's 

 experiment would seem decisive, had the entire blue light been changed into 

 another." Thus far the editor of the Acta Eruditorum. In answer to which, 

 it is to be observed, that the red and yellow which came out of the violet, and 

 the blue and violet which came out of the red, might proceed from the very 

 bright light of the sky next encompassing the sun, and that several sorts of 

 rays which come from several parts of the sun's body, are intermixed in all 

 parts of the coloured spectrum which falls on a paper at any distance from the 

 prism. In this manner of trial, for making the experiment succeed, the light 

 of the bright clouds, immediately surrounding the sun, should be intercepted 

 by an opaque skreen, placed in the open air without, at the distance of 10 or 

 20 feet from the hole through which the sun shines into the dark room. And 

 in the skreen there should be a small hole for the sun to shine through. The 

 hole may be either round or oblong, and not above -i- or -rV part of an inch 

 broad; so that the screen may intercept not only the bright light of the clouds 

 next encompassing the sun's body, but also the greatest part of the sun's light. 

 For thereby the colours will become less mixed. The beam of light which 

 passes through this hole, must afterwards pass through the other hole into the 

 dark room, and the prism must be placed parallel to the oblong hole in the 

 screen, and its refracting angle be ()0" or above. In this manner the experiment 



