It has long been the custom at the Royal Institution of Great Britain to provide each Christmastide a course of Lectures specially addressed to a juvenile audience.

On two occasions, namely, in 1881 and in 1887, the Managers entrusted this honourable duty to me. The second course was in the main a repetition of the first; and on my notes and recollections of both the present little volume has been founded.

I am indebted to my friends Rev. Maxwell Close, Mr. Arthur Rambaut, and Dr. John Todhunter for their kindness in reading the proofs.