1813.] Sir Isaac Newton. 245 



going through the usual steps, or having the assistance of any 

 person. His next book was the Arithmetic of Infinites, by Dr. 

 Wallis. On these books he wrote comments as he read them, 

 and reaped a rich harvest of discoveries, or, more properly, 

 indeed, made almost all his mathematical discoveries as he pro- 

 ceeded in their perusal. 



In 1664 he bought a prism, as appears by some of his own 

 accounts of expenses at Cambridge, to try some experiments 

 upon Descartes' doctrine of colours, and soon satisfied himself 

 that the hypothesis of Descartes was destitute of foundation. 

 The further prosecution of the subject satisfied him respecting 

 the real nature of light and colours. He soon after drew up an 

 account of his doctrine, which was published in the Philoso- 

 phical Transactions, and unfortunately gave origin to a contro- 

 versy between him and some foreign opticians, which produced 

 an unhappy effect upon his mind, and prevented him from 

 publishing his mathematical discoveries, as he had originally 

 intended. He communicated them, however, to Dr. Barrow, 

 who sent an account of them to Collins and Oldenburg, and by 

 that means they came to be known to the Members of the Royal 

 Society. 



He laid the foundation of all his discoveries before he was 24 

 years of age. In the year 1665, when he retired to his own 

 estate on account of the plague, the idea of his system of gravi- 

 tation first occurred to him, in consequence of seeing an apple 

 fall from a tree. This remarkable apple-tree is still remaining, 

 and is usually shown to strangers as a curiosity. At that time, 

 not being in possession of any accurate measure of the earth's 

 surface, he estimated the force of gravity erroneously, and found, 

 in consequence, that it was not capable alone of retaining the 

 moon in her orbit. This induced him to dismiss his hypothesis, 

 at that time, as erroneous. But afterwards, when Picard had 

 measured a degree of the earth's surface, with tolerable accu- 

 racy, he was enabled to make a more precise estimate, and found 

 that the force of gravity exactly accounted for the moon's mo- 

 tion in her orbit. He applied his doctrine to the planets and the 

 whole solar system, and found it to account, in a satisfactory man- 

 ner, for the whole phenomena of the motions of these bodies. 



In 1667 he was elected Fellow of Trinity College, in Cam- 

 bridge; and, in 1669, Dr. Barrow resigned his Mathematical 

 Professorship to him. In 1671 he was elected Fellow of the 

 Royal Society. It is stated, I do not know upon what authority, 

 that at this time he was so poor that he was obliged to apply to 

 the Society for a dispensation from the usual contribution of a 

 ■•hilling a reek, which all the Fellows of the Society regularly 

 His estate* (for be had two) were worth about 80/. a year. 



