58 M. A. Colding on the History of the 



entities whereof we arc cognizant only by their mastery over 

 nature, these entities must of course be very superior to every- 

 thing material in the world; and as it is obvious that it is 

 through them only that the wisdom we perceive and admire in 

 nature expresses itself, these powers must evidently be in rela- 

 tionship to the spiritual, immaterial, and intellectual power itself 

 that guides nature in its progress ; but if such is the case, it is 

 consequently quite impossible to conceive of these forces as any- 

 thing naturally mortal or perishable. Surely, therefore, the 

 forces ought to be regarded as absolutely imperishable (ufor- 

 gcengelige) . 



It was in accordance with this idea that I twenty years ago 

 presented to the Royal Society of Science, here in Copenhagen, 

 a treatise in which I explained my idea that force is imperishable 

 and immortal; and therefore, when and wherever force seems to 

 vanish in performing certain mechanical, chemical, or other work, 

 the force then merely undergoes a transformation and reappears 

 in a new form, but of the original amount as an active force. 



In the year 1843 this idea, which completely constitutes the 

 new principle of the perpetuity of energy, was distinctly given 

 bv me, the idea itself having been clear to my own mind nearly 

 four years before, when it arose at once in my mind by studying 

 D'Alembert's celebrated and successful enunciation of the prin- 

 ciple of active and lost forces ; but of course the new principle 

 was not as clear to me from the beginning as it was when I 

 wrote my treatise in 1843. According to the view which led 

 me to this principle, its future importance, in case it were really 

 true, was perfectly clear to me from the first instant. But this 

 made me very anxious not to publish it as a new law of nature 

 until I should be able to give experimental proof of its truth ; 

 and scientific men to whom I explained my idea, and especially 

 our celebrated Professor, H. C. (Ersted, agreed with me and 

 advised me to be safe in this respect before I wrote ; and it was 

 for this reason that I departed from my original intention of ex- 

 plaining it to a meeting of Natural Philosophers held in Copen- 

 hagen in 1840. 



In my first treatise, of 1843, the title of which is "Theses 

 concerning Force " (Nogle Satninger om Krtefterne) , I therefore 

 not only presented my idea to the Royal Society (of Copenhagen) 

 as a thing that most likely would hereafter be found to be a general 

 law of nature, but, after stating that the only trustworthy decision 

 of the question was to be got from the experimental investigation 

 of nature itself, I went on to call attention to several old experi- 

 ments made previously to my time, the first of which was Du- 

 long's celebrated discovery respecting the heat disengaged or 

 absorbed during the compression or expansion of a great number 



