Things Learned while reading “A Scandal in Bohemia - Sherlock Holmes" - Commissionaire

In mainland Europe, a commissionaire is an attendant, messenger or subordinate employed in hotels, whose chief duty is to attend at railway stations, secure customers, take charge of their luggage, carry out the necessary formalities with respect to it and have it sent on to the hotel. 

http://en.wikipedia.org/wiki/Commissionaire

Things Learned while reading “A Scandal in Bohemia - Sherlock Holmes" - Billycock

This is a billycock hat.

Things Learned while reading “A Scandal in Bohemia - Sherlock Holmes" - London's Population

In the book they mention that the population is about 4 million.  The current London Population — 7,556,900.  

Things Learned while reading “A Scandal in Bohemia - Sherlock Holmes" Over-precipitance

Over-precipitance means too much haste.  pre·cip·i·tance (-tns)

n.

1. The quality of being precipitant.

2. Action or thought marked by impulsiveness or rash haste.

Things Learned while reading “A Scandal in Bohemia - Sherlock Holmes" - Ulster

This is an ulster coat.