It is great to see someone actually checking the references The description in the article is my personal editorial freehand description of the equation on page 384 No reference Indeed I did not try to use Clausius terminology My aim was to present his idea in present day language If you feel like improving on it I will not be offended I referred to the 1850 paper to in order to defer to Clausius priority in stating the law I would still prefer to quote the 1850 paper rather than the 1865 one I have not tried to present the nearly simultaneous 1850 version by Rankine but I would not object to seeing that done as well though I think it perhaps unnecessary