Re: I understand why we don't use 'd' for density, but why rho?

Dear Chris: Yours is a very interesting question. I received a similar question some time ago concerning the symbol "B" for magnetic field intensity. Just as "B" seems to have no relationship to the word "magnetic" (or field or intensity), the symbol rho has no obvious relationship to the word "density." So the question is, who first chose the symbol "rho" to represent the concept of density? The origin and history of a word or symbol is called its "etymology," and there may be a website or other resource (dictionary of symbols, or the like) which gives the answer you seek. Sadly, I haven't found the answer yet (neither did I find the etymology of the "B" symbol). I asked a number of sources, but they could not help. I think this would be an interesting area of research. Now, it turns out, that the "rho" symbol is used not only for "density" but is also used for many other concepts, one of which is the concept of "resisitivity." Here is a clear example of why "rho" might be used for that concept, since the letter "rho" corresponds to the english letter "r." Look up the following URL: http://www.answers.com/topic/rho-2 So, I haven't found the answer to your question, but will continue to keep digging for it. By the way, if you had asked why is the english letter "c" used in physics for the velocity of light, I could tell you that it is the first letter of the Latin word for "speed" which is the word "celeritas." Most sincerely, P.M. Fichte Professor of Chemistry Coker College Hartsville, SC 29550-3797