380 PHILOSOPHICAL TRANSACTIONS. [aNNO 1794. 



It appears very probable, that a farther prosecution of these experiments on 

 coloured shadows may not only lead to a knowledge of the real nature of the har-. 

 mony of colours, or the peculiar circumstances on which that harmony depends 

 but that it may also enable us to construct instruments for producing that har- 

 mony, for the entertainment of the eyes, in a manner similar to that in which the 

 ears are entertained by musical sounds. I know that attempts have already been 

 made for that purpose ; but when I consider the means employed, I am not sur- 

 prised that they did not succeed. Where the flowing tide, the varying swell, 

 the crescendo is wanting, colours must ever remain hard, cold, and inanimate 

 masses. 



XI. Investigations, founded on the Theonj of Motion, for determining the Times 

 of Vibration of IVatch Balances. By George j^twood, Esq., F. R. S. p. 1 IQ. 



Instruments for measuring time by vibratory * motion were invented early in 

 the l6th-f- century: the single pendulum:}: liad been known to afibrd a very 

 exact measure of time long before this period ; yet it appears from the testimony 

 of historical accounts, as well as other evidences, that the balance was universally 

 adopted in the construction of the first clocks and watches ; nor was it till the 

 year l657 that Huygens united pendulums with clock-work. The first essays of 

 an invention, formed on principles at once new and complicated, we, may suppose 

 were imperfectly executed. In the watches of the early constructions, some of 

 which are still preserved, the balance vibrated merely by the impulses of the 

 wheels, without other controul or regulation : the motion communicated to the 

 balance by one impulse continued till it was destroyed, partly by friction, and 

 partly by a succeeding impulse in the opposite direction ; the vibrations must of 

 course have been very unsteady and irregular. These imperfections were in a 

 great measure remedied by Dr. Hooke's ingenious invention of applying a spiral 

 spring to the balance :§ the action of this spring on the balance of a watch, is 



* The ancients, as early as 140 years before Christ, probably much earlier, were acquainted with 

 the use of wheel-work in constmcting instruments for measuring time. " Denticuli alius alium im- 

 pellentes, versationes niodicas faciunt ac motiones," is the expression of Vitruvius in describing a ma- 

 chine one of the principal uses of which was to indicate the hour of tlie day. Vibrations are no 

 where mentioned or alluded to in the descriptions of the clocks constructed by the ancients. Dr. 

 Derham on Clock-work, p. 86,-]-th edit. — Orig. 



t About the year 1500, according to some accounts. — Orig. 



\ Tycho Brahe is supposed to have used the pendulum in astronomical observations. Riccioli, 

 Kircher, Mersenne, and many otliers, are expressly mentioned by Sturm, as having employed tliis 

 method of measuring time. — Orig, 



§ Anno 16'58. — An inscription on a balance-spring watch, presented to King Charles II. fixes the 

 date of tills invention to the year l658. Dr. Derham relates, that he had seen tiie watch, on which 

 the following inscription was engraven : "Robert Hooke iiiven. l6"38. T. Tompion fecit, Ui75." 

 Dr. Derham on Clock-work, p. 103. — Orig, 



