Trivia: In the video documenting the making of The Time Machine, Rod Taylor states that if you count the number of rivets on the spinning disk on the back of the machine, there are 365 of them (one for each day of the year). That said, there are actually only 348 pegs.
Trivia: If you look closely at the metal plate that is connected to the front of the machine it says, "Manufactured by H. George Wells".
Trivia: In the book, the Time Traveler finds a museum in 'The Palace of Green Porcelain'. Though this isn't mentioned in the film in any way, the room the 'speaking rings' are in has bright green walls. Nice touch.
Answer: Earlier in the movie, Mrs. Watchit hands an envelope to Philby with a note inside to inform everyone that if George doesn't show up at 8:00, then they can start dinner without him. This is what he most likely left on the mantle before he started his journey through time.