From the outset of his college career, Newton’s attention seems to have been mainly directed to mathematics.  Here he began to give evidence of that marvellous insight into the deep secrets of nature which more than a century later led so dispassionate a judge as Laplace to pronounce Newton’s immortal work as pre-eminent above all the productions of the human intellect.  But though Newton was one of the very greatest mathematicians that ever lived, he was never a mathematician for the mere sake of mathematics.  He employed his mathematics as an instrument for discovering the laws of nature.  His industry and genius soon brought him under the notice of the University authorities.  It is stated in the University records that he obtained a Scholarship in 1664.  Two years later we find that Newton, as well as many residents in the University, had to leave Cambridge temporarily on account of the breaking out of the plague.  The philosopher retired for a season to his old home at Woolsthorpe, and there he remained until he was appointed a Fellow of Trinity College, Cambridge, in 1667.  From this time onwards, Newton’s reputation as a mathematician and as a natural philosopher steadily advanced, so that in 1669, while still but twenty-seven years of age, he was appointed to the distinguished position of Lucasian Professor of Mathematics at Cambridge.  Here he found the opportunity to continue and develop that marvellous career of discovery which formed his life’s work.

The earliest of Newton’s great achievements in natural philosophy was his detection of the composite character of light.  That a beam of ordinary sunlight is, in fact, a mixture of a very great number of different-coloured lights, is a doctrine now familiar to every one who has the slightest education in physical science.  We must, however, remember that this discovery was really a tremendous advance in knowledge at the time when Newton announced it.

[Plate:  Diagram of A sunbeam.]

We here give the little diagram originally drawn by Newton, to explain the experiment by which he first learned the composition of light.  A sunbeam is admitted into a darkened room through an opening, H, in a shutter.  This beam when not interfered with will travel in a straight line to the screen, and there reproduce a bright spot of the same shape as the hole in the shutter.  If, however, a prism of glass, A B C, be introduced so that the beam traverse it, then it will be seen at once that the light is deflected from its original track.  There is, however, a further and most important change which takes place.  The spot of light is not alone removed to another part of the screen, but it becomes spread out into a long band beautifully coloured, and exhibiting the hues of the rainbow.  At the top are the violet rays, and then in descending order we have the indigo, blue, green, yellow, orange, and red.