Vlll PREFACE. 



is now no toy, but is recognised as a valuable aid to 

 education far and wide. The reason for this is not 

 far to seek. First, we have to look at the vast 

 improvement in the instrument itself. So long as the 

 greasy, evil-smelling oil lamp was almost the sole 

 illuminant available, and roughly executed daubs in 

 varnish colours on glass the only works of art (?) 

 which could be purchased for the lantern, it did not much 

 signify that the lenses were also of a faulty character, 

 and no better in quality than the " bull's eye " of the 

 nocturnal policeman. But when the brilliant limelight 

 came to be adapted to the lantern, it was at once seen 

 that the capabilities of the instrument were not only 

 much increased, but almost without limit. It would 

 be difficult to say offhand how many persons visited 

 the Royal Polytechnic Institution in the forty years 

 during which it was open to the public; but it is 

 within my own experience that at one period, at the 

 time of the ( ' ghost " illusion, they came at 

 the rate of two thousand per diem. There is no 

 doubt whatever that the Polytechnic caused this form 

 of amusement to become popular, for the lecturers 

 affiliated to the Institution travelled the country 

 round, and gave similar entertainments in all parts. 



There are few branches of science in which the 

 optical lantern cannot be made useful for purposes of 

 demonstration, and as this fact becomes better known, 

 every schoolroom in the kingdom will be provided 

 with one. In every lecture theatre worthy of the 



