Boys achieved recognition as a scientist for his invention of the fused quartz fibretorsion balance, which allowed him to measure extremely small forces. He made the fused quartz fibres for his instrument by attaching a quartz rod to a crossbow quarrel, heating the rod to the point of melting, and firing the crossbow. By this means he produced fibre so thin that it could not be resolved with an optical microscope. He used this invention to build a radiomicrometer capable of responding to the light of a single candle more than one mile away, and used that device for astronomical observations. In 1895 he published a measurement of the gravitational constantG that improved upon the accuracy achieved by Cavendish. Boys' method relied on the same theory as Cavendish's, but used two masses suspended at one height and two nearby masses suspended at a different height, to minimise the unwanted interaction between opposite masses. He was a critic of the solar engine design of Frank Shuman, so Shuman hired him, and together they patented a ":File:US Patent 1240890.pdf|Sun-Boiler", which is similar to modern dayparabolic troughsolar power plants.
In 1897 Boys became a Metropolitan Gas Referee, charged with assessing a fair price for coal gas. He initially worked on the replacement of the standard candle, used to determine the quality of the gas for lighting, by the Harcourt pentane lamp. As heating grew to become the principal use of coal gas, Boys undertook fundamental work on calorimetry to measure and record the heat content of the gas, achieving a substantial increase in precision of measurement. At this time the national gas bill for the United Kingdom was fifty million pounds, so a one-percent correction to the bill represented a very significant amount of money. Boys also worked on high-speed photography of lightning and bullets in flight, and conducted public lectures on the properties of soap films, which were gathered into the book Soap Bubbles: Their Colours and the Forces Which Mould Them, a classic of scientific popularisation. The first edition of Soap Bubbles appeared in 1890 and the second in 1911; it has remained in print to this day. The book deeply impressed French writerAlfred Jarry, who in 1898 wrote the absurdist novel Exploits and Opinions of Dr. Faustroll, Pataphysician, in which the title character, who was born at the age of 63 and sails in a sieve, is described as a friend of C.V. Boys. The book was also a favourite of American poet, Elizabeth Bishop.
Boys married Marion Amelia Pollock in 1892. She caused a scandal by having an affair with the Cambridge mathematician Andrew Forsyth, as a result of which Forsyth was forced to resign his chair. Boys divorced Marion in 1910 and she later married Forsyth. He died at St Mary Bourne, Andover in Hampshire on 30 March 1944.