1857.] On the Conservation of Force. 443 



were then interposed in the course of the ray, but I could not 

 perceive when any portion of a ray passed (and that was gene- 

 rally the case) that it differed sensibly in colour or quality from 

 the ray passing into the preparation. In like manner, the ob- 

 jects were put into the differently coloured rays and observed 

 by the reflected light, a lens being sometimes employed to con- 

 centrate the light ; but I could not find any marked difference 

 between the colour or character of the ray reflected and the 

 impinging ray, except in quantity. 



On the Conservation of Force*. 



VARIOUS circumstances induce me at the present moment to 

 put forth a consideration regarding the conservation of force. 

 I do not suppose that I can utter any truth respecting it that 

 has not already presented itself to the high and piercing in- 

 tellects which move within the exalted regions of science ; but 

 the course of my own investigations and views makes me think 

 that the consideration may be of service to those persevering 

 labourers (amongst whom I endeavour to class myself), who, 

 occupied in the comparison of physical ideas with fundamental 

 principles, and continually sustaining and aiding themselves by 

 experiment and observation, delight to labour for the advance 

 of natural knowledge, and strive to follow it into undiscovered 

 regions. 



There is no question which lies closer to the root of all phy- 

 sical knowledge, than that which inquires whether force can be 

 destroyed or not. The progress of the strict science of modern 

 times has tended more and more to produce the conviction that 

 " force can neither be created nor destroyed," and to render 

 daily more manifest the value of the knowledge of that truth in 

 experimental research. To admit, indeed, that force may be 

 destructible or can altogether disappear, would be to admit that 

 matter could be uncreated ; for we know matter only by its 

 forces : and though one of these is most commonly referred to, 

 namely gravity, to prove its presence, it is not because gravity 

 has any pretension, or any exemption amongst the forms offeree, 

 as regards the principle of conservation ; but simply that being, 

 as far as we perceive, inconvertible in its nature and un- 

 * Proceedings of the Royal Institution, Feb. 27, 1857, vol. ii. p. 352. 



