Todhunter, I. (1859) Spherical Trigonometry for the Use of Colleges and Schools.
https://books.google.hu/books?id=2uoDAAAAQAAJ&printsec=frontcover&hl=hu&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

has been cited by the following article:

• TITLE: The Right Triangle as the Simplex in 2D Euclidean Space, Generalized to n Dimensions

  AUTHORS: István Lénárt

  KEYWORDS: Cycles of Incidence, Quadrirectangular Tetrahedron, Rectangular Pentachoron, Generalization of Pythagoras Theorem, Volume of a Rectangular Simplex, Cayley-Menger Determinant

  JOURNAL NAME: Journal of Applied Mathematics and Physics, Vol.10 No.9, September 30, 2022

  ABSTRACT: The purpose of the research is to show that the general triangle can be replaced by the right-angled triangle as the 2D simplex, and this concept can be generalized to any higher dimensions. The main results are that such forms do exist in any dimensions; meet the requirements usually placed on an n-dimensional simplex; a hypotenuse and legs can be defined in these shapes; and a formula can be given to calculate the volume of the shape solely from the legs by a direct generalization of the Pythagorean Theorem, without computing the Cayley-Menger determinant.