Nigel Williams' Practical Hat Opera Glasses
Why is it that, whenever you have taken the utmost care to get a ticket for the best seat in the Opera House, you turn up and find a gentleman has taken his place in the seat in front of you who does not care to remove his top hat? Infuriating as that might be, there is now an answer to this problem, as long as you take along your Practical Hat Opera Glasses. These are designed to allow you to see over the top of the gentleman's hat, by siting the outer lenses considerably higher than the viewing lenses at the inner end - just like the periscope in one of those new-fangled submarine contraptions.
Explore more details of this intriguing device, including a video