220 HISTORY OF SCIENCE. 



brought to a common focus by passing through a large convex lens, they 

 reproduced white light. Another experiment adopted consisted in at- 

 tempting to produce a white substance by mixing coloured pigments. 

 But coloured powders are by their nature very different from the pure 

 colours of the spectrum, and pigments which appear to the eye nearly of 

 the same one colour produce very different effects when they are mixed 

 with another. One of Newton's mixtures was formed of one part of red 



lead, four parts of blue bice>&\\& a proper 

 proportion of orpiment and verdigris. 

 This mixture of red, blue, yellow, and 

 green pigments appeared nearly of the 

 colour of clean sawdust. A very ele- 

 gant and easy method of recompound- 

 ing white light is to take a circular 

 piece of cardboard, divide into sec- 

 ^ ons as shown in Fig. 105, and paint 

 these with the colours named. When 

 suc h a disc is made to revolve very 

 rapidly on a pin passed through its 

 ^ centre, the disc appears very nearly 



white. 



Newton deduced from the facts he had discovered that all the shades 

 of colour which appear in objects can be imitated by intercepting cer- 

 tain rays of the spectrum and uniting the rest, and that a body cannot 

 present a colour which is not contained in the incident light ; and that 

 the colours of bodies are not qualities inherent in the bodies them- 

 selves, but arise from the disposition of the particles of each body to 

 absorb certain rays, and thus to reflect more copiously the other rays. 

 No sooner were these experiments and inferences announced than 

 Newton's views were vigorously and pertinaciously attacked ; but 

 Newton triumphantly refuted all objections, though it perhaps cost 

 him more trouble to detect his adversaries' blunders than to discover 

 the truth they attempted to impugn. 



It will be unnecessary here to enter into these and other contro- 

 versies which Newton held with various persons. Among the dispu- 

 tants on this and other occasions was a man of very original powers, 

 who only just failed to become one of the very greatest men of science 

 of his time. This was DR. ROBERT HOOKE (1638 1703), who was 

 one of the original members of the Royal Society. Hooke had great 

 versatility of talent, and his acquirements were numerous and exten- 

 sive ; but he lacked fixedness of purpose. He could, but for the want 

 of patient perseverance, and but for certain defects of remper, have 

 rivalled Newton himself. Many are the ingenious inventions which 

 attest the practical turn of his genius, and many more are the inven- 

 tions which he left in an unfinished or imperfect condition. The like 

 divergence in his speculations often turned him aside on the very 



