Sir David Brewster, in his work on natural magic, has the following to say about concave mirrors and the art of phantasmagoria: “Concave mirrors are distinguished by their property of forming in front of them, and in the air, inverted images of erect objects, or erect images of inverted objects, placed at some distance beyond their principal focus. If a fine transparent cloud of blue smoke is raised, by means of a chafing dish, around the focus of a large concave mirror, the image of any highly illuminated object will be depicted in the middle of it, with great beauty. A skull concealed from the observer is sometimes used to surprise the ignorant; and when a dish of fruit has been depicted in a similar manner, a spectator, stretching out his hand to seize it, is met with the image of a drawn dagger which has been quickly substituted for the fruit at the other conjugate focus of the mirror.” {92} Thoroughly conversant with the science of optics, it is more than probable that Robertson made use of large concave mirrors to project inverted phantoms of living persons in the air, with convex lenses to restore the ghosts to an upright position. If he merely used painted images, which is the more likely, then he had resort to the phantasmagoric magic lantern, rolling upon a small track. Pushing this contrivance backwards and forwards caused the images to lessen or increase, to recede or advance. Robertson realized quite a snug fortune out of his ghost exhibition and other inventions. His automaton speaking figure, called _le phonorganon_, uttered two hundred words of the French language. Another interesting piece of mechanism was his Trumpeter. These two machines formed part of a beautiful _Cabinet de Physique_ in his house, the Hotel d’ Yorck, Boulevard Montmartre, No. 12 Paris. He has left some entertaining memoirs, entitled _Mémoires récréatifs et anecdotifs_ (1830–1834), copies of which are exceedingly rare. He was a great aeronaut and invented the parachute which has been wrongly attributed to Garnerin. Robertson, as _Commandant des Aerostiers_, served in the French army, and rendered valuable service with his balloons in observing the movements of the enemy in the campaigns in Belgium and Holland, under General Jourdain. In the year 1804 he wrote a treatise on ballooning, entitled, _La Minerve, vaisseau Aérien destiné aux découvertes, et proposé, à toutes les Académies de l’Europe_, published at Vienna. He died at Batignolles (Paris) in 1837. In his memoirs, Robertson describes a species of optical toy called the Phantascope, for producing illusions on a small scale. This may give a clue to his spectres of the Capuchin Convent. He also offers an explanation of Nostradamus’ famous feat of conjuring up the likeness of Francis I. in a magic mirror, for the edification of the beautiful Marie de Médici. II.