Qn correcting the Rate of an Electric Clock. 203 



very little, if at all, elevated above that of the surrounding at- 

 mosphere in which they are placed. And further, many sub- 

 stances are capable of attaining a very high degree of tempera- 

 ture, and becomip.g highly attenuated, (as for example, when 

 water is converted into steam.) vi'ithout emitting the least degree 

 of light. Heat parses through all bodies, with greater or less 

 facility; whereas light only passes through those bodies which 

 are termed transparent : — and many substances that transmit 

 light very freely, are at the ssme time very bad conductors of 

 heat. Hence it would appear, that heat and light are two di- 

 stinct agents. Whether light be a fluid, or only a property of 

 matter, or consists of an innumerable quantity of small particles 

 emitted from a luminous body, remains yet to be determined. 

 The phtenomena of light appear to admit of the best explana- 

 tion, according to the latter supposition; and the late discovery 

 of Malus, respecting light having a polarity, may be adduced as 

 another argument in its favour. 



XXXVI. On Correcting the Rate of an Electric Clock by a 



Compensation for Changes of Temperature. 



By F. Ronalds, Esq. 



To Mr. Tilloch. 



Sir, — ItIaving at different intervals, since my communication 

 to you in April last, made fresh attempts to render Mr. De Luc's 

 column applicable to tlie measure of time, and being now obliged 

 to discontinue them by a long absence from London, permit me 

 to describe that which has been most successful, in the hope that 

 some person better qualified for the subject may deem it worthy 

 of attention. 



I have, by the following method, procured a better compensa- 

 tion for the effect of an increase of temperature, which, by in- 

 creasing the power of the column, accelerates the velocity of the 

 vibrations. 



A beam, is suspended like a dipping needle, as nearly as pos- 

 sible in its centre of gravity, carrying at one end the clock, and 

 at the other a weight almost counterpoizing it. A spirit ther- 

 mometer of nearly the same kind as those used in France (to 

 mark the degree of heat by an index) is placed under the beam; 

 the part containing the spirit is 35 inches long, and one inch 

 bore, and the part which contains in its lower end the mercury 

 is half an inch bore. A small ivory rod and piston sliding very 

 freely in the latter tube rests upon the surface of the mercury, 

 and gubtains at its upper end the preponderating weight of that 



arm 



