In Riemannian geometry, the "lowering indices" operator is denoted by $\flat:TM \to T^*M$ and the "raising indices" operator by $\sharp:T^*M \to TM$. These isomorphisms are sometimes referred to as musical isomorphisms, as stated on [Wikipedia][1] and in [several][2] [other][3] [sources][4]. Surely, the motivation for such terminology is clear. I would nevertheless like to know who decided to adpot these (rather amusing) notations, so here is a question:

What was the first paper / textbook that made use of the notations $\flat$ and $\sharp$?

and a possible follow-up question:

If such notations were not adopted widely after the first appearance, who popularized them? [1]: http://en.wikipedia.org/wiki/Musical_isomorphism [2]: http://www.math.sunysb.edu/~brweber/401s09/coursefiles/Lecture12.pdf [3]: http://www.math.washington.edu/~chieca/Teaching/Spring11/Materials/Forms.pdf [4]: http://math.uh.edu/~minru/Riemann09/bochnerhodge.pdf

In Riemannian geometry, the "lowering indices" operator is denoted by $\flat:TM \to T^*M$ and the "raising indices" operator by $\sharp:T^*M \to TM$. These isomorphisms are sometimes referred to as musical isomorphisms, as stated on Wikipedia and in several other sources. Surely, the motivation for such terminology is clear. I would nevertheless like to know who decided to adpot these (rather amusing) notations, so here is a question:

What was the first paper / textbook that made use of the notations $\flat$ and $\sharp$?

and a possible follow-up question:

If such notations were not adopted widely after the first appearance, who popularized them?