Cowles's patented invention was in two parts: a cone-type variable-speed drive and a method of holding in the headstock spindle a draw-in collet, or 'chuck' (or sometimes split-chuck) as they were then known. However, the concept of an infinitely variable-speed drive, using two opposing cones with some sort of friction material trapped between and sliding along them to transfer the drive, was not new, for it appears to have been similar to one granted a patent by Otis Pettee on March 25th 1825 and described as "Pettee, Otis; changing the motion of machinery, Newton MA". Otis Pettee (1817-1853) lived in Newton Upper Falls, and founded the Pettee Machine Works, a company that manufactured cotton machinery. Unfortunately, patents taken out before 1836 are unavailable; they were destroyed in a fire that year, and so precise details of Pettee's invention are not known.
A much larger unit of this kind, capable of handling up to 50 h.p., had been devised by Mr. George P. Evans, of Newton Centre, and manufactured by his company, The Evans Variable Speed Cone Co. and called, naturally enough, the Evans Friction Cone. However, Evans' patents are dated after the one taken out by Cowels, with his first listed eleven years later, in 1884. If Evans knew of the Cowels patent, he must have managed to alter some detail to get around it, possibly by the better idea of using a wide flat leather belt
Unusually for a patent, that for the Cowles lacks several details, including how the friction wheel between the two cones was moved to change speed. However, might this have been thought to be obvious - and the bar upon which the friction wheel ran could be grasped where it might have emerged from the end face of the headstock. The Pettee method of varying the speed was equally simple, with a cord attached to the leather belt and a handy pivoting lever to move it as required (shown in the pictures below).
In addition to the variable-speed mechanism, another feature unique to the Cowles watchmakers' lathe was the method of holding the collet. Instead of a draw-in bar or tube, a catch was used, this being shown in Fig.3 and consisted of a pivoting arm (called a dog "l" in the patent) that rested in a notch formed towards the outer end of the collet's shaft (M). The stated aim was that a cut, diagonally clean through the end of Pulley (E) along the line 'k' to 'k', would, as the pulley started to move, cause it to move to the left and so push the end of the lever against the notch and hold the collet firmly in place. However, the patent fails to explain how the pulley (E) is connected to the headstock spindle (G) - and it's necessary to deduce from the following that the shoulder (J) must have been separate from the central part of (E) and fastened to the spindle to rotate it. "....A and head-stock C are two cone  pulleys, E and F; the upper one, E, is free to move on the hollow mandrel G …...the pulley E is placed on a hollow mandrel G, having a shoulder, j, against which the large part of the pulley bears." Might any reader have another explanation?