in 1933 milne-thomson published his first book, "the calculus of finite differences" which became a classic textbook and the original text was reprinted in 1951. in the mid 1930s, milne-thomson developed an interest in hydrodynamics and later in aerodynamics. this led to publication of two popular textbooks titled "theoretical hydrodynamics" and "theoretical aerodynamics". the theoretical hydrodynamics published by macmillan & co. ltd., london, appeared in 1938 and more material based on his own research was added in the subsequent editions of this classic book. the fifth edition appeared thirty years later in 1968. the book was republished by dover publications in 1996. similarly, theoretical aerodynamics, first published in 1948, went through a number of editions with the fourth appearing in 1968.