56 



THE POPULAR EDUCATOR. 



it is shown at Fig. 2, in which T T is the tube ; the top contain- 

 ing the first mirror is placed just above the edge of the wall, 

 and directed to the object o, and the image being reflected 

 in the tube from A to the second mirror, B, is seen by the observer, 

 who, of course, unlike the silly ostrich, has not only his head 

 but his whole body protected from the searching and disagree- 

 able shower of lead which the enemy is always kind enough to 

 furnish. The police might occasionally use them with good 

 effect, whilst engaged in watching intending depredators, the 

 sharp Arabs of European race and reputation. 



In the Encyclopedic Mtthodique of Montucla, the refined 

 French philosopher says, " Comme il est impoli de lorgner avec 

 attention une personne, on a imagine en Engleterre une sorte de 

 lorgnette au moyens de laquelle, en paroissant considerer un objet, 

 ou on regarde reellement un autre." Manners have changed 

 since this was written, and instead of it being thought rude to 

 stare people out of countenance, it is now considered quite the 

 ton to use the eyes alone, and better with an eye-glass, and better 

 still with an opera-glass, particularly if royalty happen to be at 



place during the time of a siege. It consisted of a tube bent 

 in such a manner as to form two elbows, in each of which 

 was a plane mirror inclined at an angle of 45. The first part 

 of the tube was made to rest on the parapet towards the enemy ; 

 the image reflected by the first inclined mirror passed through 

 the tube in a perpendicular direction, and meeting with the 

 second mirror, was reflected horizontally towards the eye-glass 

 when the eye was applied ; by these means a person behind a 

 strong parapet could see what the enemy were doing without 

 the walls. The chief thing to be apprehended in regard to this 

 instrument was, that the object-glass might be broken by a 

 ball ; but this was certainly a trifling misfortune, and not very 

 likely to happen," certainly not, considering that " Old Brown 

 Bess " would hit nothing at any distance greater than 200 

 yards. 



The above account shows that Mr. Taylor's instrument is 

 made in a simpler manner, and that whilst the military men 

 were unacquainted with the fact that Dr. Hutton, one of their 

 own teachers of mathematics at Woolwich, had mentioned 



the place of entertainment. Montucla having, as it were, 

 apologised for the instrument, then proceeds to describe it : 

 "Adapt to the end of an opera-glass (Fig. 3), o o (the object- 

 glass of which in this case becomes useless for direct vision), 

 a tube, A A A, pierced with a lateral aperture, B, of the same size 

 as that of the tube of the opera-glass ; behind this aperture, B, 

 place a small mirror, inclined 45 to the axis of the tube, and 

 having its reflecting surface turned towards the object-glass, r>. 

 It is evident that when this glass is directed to any object 

 vis-a-vis (opposite to yourself), that other things or persons at 

 the side only will become visible namely, those situated near 

 the line drawn from the eye in the direction of the axis of the 

 lorgnette, and reflected by the mirror. These objects will 

 appear upright, but transposed from right to left. In addition 

 to which, and to disguise the artifice better, the front part of 

 the lorgnette may be furnished with a plane glass, which will 

 give the instrument all the appearance of a real, honest, 

 straightforward-looking opera-glass." 



Dr. Button, in commenting on this contrivance, says, " We 

 must, however, observe that the first idea of this instrument is 

 not very new, for the celebrated Hevelius, who, it seems, was 

 afraid of being shot (who is not ?), proposed many years ago 

 his polemoscope, a telescope for viewing under cover, without 

 danger, warlike operations, and those in particular which take 



such a contrivance, it remained for a clergyman to direct the 

 attention of soldiers again to this life-saving apparatus ; at least 

 those who were afraid of being shot. 



" It is possible," declares the learned Montucla, "to perform 

 many curious tricks with plane mirrors, which may surprise, 

 nay, embarrass those persons who are ignorant of the laws of 

 catoptrics." He then explains how to fire a pistol over the 

 shoulder with just as good an aim as if it was fired in the 

 ordinary manner. The optical duellist places himself before a 

 plane mirror, A B (Fig. 4), which is so arranged that he can see 

 the image of a plaster-cast reflected in it ; he then rests the 

 barrel of the pistol on his shoulder, s, and takes aim, covering the 

 plaster image with the muzzle of the weapon ; in fact, aiming 

 the pistol at the reflected instead of at the real object. It is 

 evident, by looking at the reflector, A B, that if the hand is 

 steady, and the aim good, the crash of the figure behind the 

 shooter will proclaim to the spectators that, optically speaking, 

 a marksman may turn his back on his enemy and yet shoot him. 



Another amusing experiment is to construct a box in which 

 heavy bodies like a ball of lead appear to run up an inclined 

 plane, instead of gravitating in the contrary direction. 



Let a carpenter construct an ordinary four-sided box, A B c D. 

 In the drawing (Fig. 5), one side is removed, or it may, in 

 fact, be hung on hinges, and open like a door, in order to show 



