Newton having to do with chemistry. During this period, Newton studied several areas of work including religion, calculus and chemistry. According to Alfred Rupert Hall the first practical reflecting telescope was built by Newton in 1668. Later on such prototype for a design came to be called a Newtonian telescope or Newton's reflector. On 21 December 1671 he was proposed as a candidate for admission to the Royal Society by Dr Seth Ward, bishop of Salisbury, and on 11 January 1672, he was elected a fellow of the Society. At the meeting at which Newton was elected, he read a description of a reflecting telescope which he had invented, and "it was ordered that a letter should be written by the secretary to Mr. Newton to acquaint him of his election into the Society, and to thank him for the communication of his telescope, and to assure him that the Society would take care that all right should be done him concerning this invention." In his reply to the secretary on 18 January 1672, Newton writes: "I desire that in your next letter you would inform me for what time the society continue their weekly meetings; because, if they continue them for any time, I am purposing them to be considered of and examined an account of a philosophical discovery, which induced me to the making of the said telescope, and which I doubt not but will prove much more grateful than the communication of that instrument being in my judgment the oddest if not the most considerable detection which hath hitherto been made into the operations of nature." This promise was fulfilled in communication which Newton addressed to Henry Oldenburg, the secretary of the Royal Society, on 6 February 1672, and which was read before the society two days afterward. The whole is printed in No. 80 of the Philosophical Transactions. Newton's "philosophical discovery" was the realisation that white light is composed of a spectrum of colours. He realised that objects are coloured only because they absorb some of these colours more than others. After he explained this to the Society, he proceeded: "When I understood this, I left off my aforesaid glassworks; for I saw, that the perfection of telescopes was hitherto limited, not so much for want of glasses truly figured according to the prescriptions of Optics Authors (which all men have hitherto imagined), as because that