MYSTEKIOUS DAGGER. 63 



obstruction to an eye at O, are reflected as it 

 were from those minute particles of which the 

 smoke is composed, in the same manner as a 

 beam of light is rendered more visible by passing 

 through an apartment filled with dust or smoke. 



It has long been a favourite experiment to 

 place at A a white and strongly illuminated 

 human skull, and to exhibit an image of it amid 

 the smoke of a chafing-dish at B; but a more 

 terrific effect would be produced if a small skeleton 

 suspended by invisible wires were placed as an 

 object at A. Its image suspended in the air at 

 B, or painted upon smoke, could not fail to 

 astonish the spectator. 



The difficulty of placing a living person in an 

 inverted position, as an object at A, has no doubt 

 prevented the optical conjuror from availing him- 

 self of so admirable a resource ; but this diffi- 

 culty may be removed by employing a second 

 concave mirror. The second mirror may be so 

 placed as to reflect towards MN the rays 

 proceeding from an erect living object, and to 

 form an inverted image of this object at A. An 

 erect image of this inverted image will then be 

 formed at B, either suspended in the air, or 

 depicted upon a wreath of smoke. This aerial 

 image will exhibit the precise form and colours 

 and movements of the living object, and it will 

 maintain its character as an apparition if any 

 attempt is made by the spectator to grasp its un- 

 substantial fabric. 



A deception of an alarming kind, called the 

 Mysterious dagger, has been long a favourite ex- 

 hibition. If a person with a drawn and highly 

 polished dagger, illuminated by a strong light, 



