This trick in which a shot-glass of liquid is vanished in the hands is commonly credited to Percy Abbott, who released it in 1934. It has been suggested that Abbott purloined the trick from Dr. Boris Zola, but the history is more complex than that.
Max Sterling, in Problems in Mystery, 1909, p. 39, explained a method for vanishing a glass of water from the hands. Harry Whitely, the publisher of Sterling's book, credited this method to the English magician Prof. Whyman (c. 1864-1904). Whyman's method used a half rubber ball to seal the mouth of the glass, and a sucker on a cord to be stuck to the bottom of the glass for the vanish. When released, the glass dropped on the cord and swung under the coat. The glass was a drinking glass, larger than a shot glass, and its disappearance was effected under cover of a sheet of newspaper or a handkerchief.
The Zola-Abbott method, using a full rubber ball on a elastic cord as both the sealer and the pull, was an economical simplification. However, crediting “Squash” to Zola is partially misleading. Zola used his ball on cord gimmick to produce a glass of liquid. He used the gimmick in a routine he marketed in 1933 as “Glasses from Nowhere” (see his ad in The Linking Ring, Vol. 13 No. 2, Apr. 1933, p. 120). Abbott may have recognized the improvement offered by Zola's gimmick and reversed its application from an arrival to a departure of a small glass; or he may known of the old Whyman trick and adapted Zola's form of gimmick to it, reducing the size of the glass so that only cover provided by the hands was required, making the trick practical for close-up performance. (Researched by Bill Mullins.)