Timothy Pride points out that stolen money is generally laundered before being passed on. 'In the light of previous questions and answers', he says, 'it is well established that objects emerge from the washing machine inside-out. Perhaps N Fowler should check the serial numbers of any money he receives to ensure that they are the right way round.'
Graham Main sees it from a physicist's viewpoint: 'Doppler supplied an answer years ago. The recipient sees the money travelling towards him and the light coming from it shifts to the blue part of the visible spectrum, thus the used notes attain a true blue colour and are clearly honestly earned.
'However, to an observer of the transaction viewing the money travelling away from him, red shift occurs, and to him it is obvious that the money changing hands has been stolen.'
Nobody suggested that a Doppler effect might explain C McKane's soap lather, which is always white, whatever the colour of the soap. Otto Black believes the reason is 'that the soap, in becoming suds, has already commenced its indiscriminate cleansing action, and thus washes itself.'
Tim Appleton, however, describes an analogous phenomenon which cannot be explained purely by cleansing: 'If Guinness is black, why is its head white?'
This week's questions: Why do women button their shirts to the left and men to the right? (Miss S Al-Benna), why do tennis umpires call '15 all' rather than '15 both'? (George Oliver), why is 11 Downing Street next to 10 Downing Street, rather than on the other side of the road? (Bob McCulloch) and why do mail order firms use the lunar calendar (as in 'Please allow 28 days for delivery')? (Frank Adey).
Answers and more questions should be sent to Silly Question, The Independent, 40 City Road, London, EC1Y 2DB.Reuse content