At this stage Watt himself was more fertile in mechanical inventions than in any other portion of his busy life. Taking his patents in their chronological order, the first (subsequent to that of 1769) was "For a new method of copying letters and other writings expeditiously," by means of copying _presses_. Of the same date was his invention of a machine "for drying linen and muslin by steam." On October 25, 1781, he took out his third patent (the second of the steam-engine series), "for certain new methods of applying the vibrating or reciprocating motion of steam or fire engines, to produce a continued rotative motion round an axis or centre, and thereby to give motion to the wheels of mills or other machines." One of these methods was that commonly known as the _sun-and-planet wheels_; they were five in all. A favorite employment of his in the workshops at Soho, in the later months of 1783 and earlier ones of 1784, was to teach his steam-engine, now become nearly as docile as it was powerful, to work a tilt-hammer for forging iron and making steel. "Three hundred blows per minute--a thing never done before," filled him, as his biographer says, with feelings of excusable pride. Another patent in the steam-engine series, taken out in 1784, contained, besides other methods of converting a circular or angular motion into a perpendicular or rectilineal motion, the well-known and much-admired _parallel motion_, and the application of the steam-engine to give motion to wheel-carriages for carrying persons and goods. To ascertain the exact number of strokes made by an engine during a given time, and thereby to check the cheats of the Cornish miners, Watt also invented the "Counter," with its several indexes. Among his leading improvements, introduced at various periods, were the _throttle-valve_, the application of the _governor_, the _barometer_ or float, the _steam-gauge_, and the indicator. The term during which he seems to have thus combined the greatest maturity with the greatest activity of intellect, and the portion of his life which they comprehended, was from his fortieth to his fiftieth year. Yet it was a term of increased suffering from his acute sick-headaches, and remarkable for the infirmities over which he triumphed; notwithstanding, he himself complained of his "stupidity and want of the inventive faculty."