14 



HA RD WICKE'S SCIENCE- G OS SIP. 



stating that " the curvature of the surface is altered 

 by the greater or less rigidity of the figures, and thus 

 the foci of these parts are thrown at a greater or less 

 -distance from the mirror." 



(5) Professors Ayrton and Perry also account for it 

 as arising from inequality of curvature, and at the 

 Royal Society, and Royal Institution, gave admirable 

 •explanations of it. 



Struck by the fact (discovered by Professor 

 Atkinson) that a small scratch made by a nail on 

 the back (of one of these mirrors) was reflected as 

 a bright patch on the screen, Professor Ayrton 

 examined several mirrors to ascertain, if possible, the 

 cause. He found that all those possessing the magic 

 property were thin, and slightly convex. He next 

 inspected their manufacture, and found that the 

 surface of each half of the mould in which they were 

 cast was flat. How did they become convex ? He 

 found that this arose partly from the tool with which 

 the makers worked, and partly from the process of 

 polishing. 



The rough mirror was first made smooth with a hand- 

 scraping tool ; then the metal was worked with the 

 megebo (" distorting-rod"), which makes the mirror 

 jreally concave at the surface ; but it receives a kind 

 ■of "buckle," and springs back again, the surface be- 

 coming convex on the removal of the pressure of the 

 distorting-rod. The thinner parts under the operation 

 have a tendency to become more convex than the 

 thicker. Hence it occurred to Professors Ayrton and 

 Perry that the employment of different beams of 

 .light (convergent, divergent, parallel) would give the 

 solution to the mystery. For if the magic power 

 was caused by the molecular differences of the 

 surface, the varied beams of light would make no 

 practical difference ; but, if it resulted from inequality 

 of the curvature of the surface, then a converging 

 beam of light would invert the phenomenon. This 

 .experiment proved to be the case. 



The following summary will give some notion 

 of the methods of Professors Ayrton and Perry's 

 reasoning. 



Let HH (Fig. 5) = Japanese convex mirrors. 



Let xa, XB, xc = rays of a parallel beam of light. 



Let AD, AE, CF = reflected rays on the screen. 



Let DF = screen. 



Let AB, BC = each other, then the amount of light 

 falling on each will be equal. 



If a portion (bc) of the mirror be flatter than the 

 remainder, then the reflected light will only illu- 

 minate a smaller area, GK ; but, as this smaller area 

 has received the same amount of light as the larger, 

 de, therefore it will be brighter than the larger, but 

 the intervening spaces (GE, KF) will be relatively 

 dark. 



The same reasoning applies to Fig. 6 = diverging 

 beam of light. 



Fig. 7 shows us the result of a converging beam of 

 •light. 



Let xxx = rays of a beam of light converging to a 

 point behind the convex surface of the mirror (nearer 

 to the surface than half the radius of the mirror) ; 

 after being reflected, the light converges to a point o 

 in front of the mirror, its rays crossing, spread them- 

 selves out in an inverted position on the screen DF. 



If ab is flatter than the rest of the surface of the 

 mirror (say bc), it casts a paler and a larger reflection 

 of light on the screen (placed at a distance) than EC 

 does (see Fig. 7). If the screen be moved nearer the 

 mirror, as P (see Fig. 7), the reflection from ab is not 

 larger, etc., than the reflection from BC. 



When the screen is placed very near the mirror, 

 the reflections of the figures will be invisible, from 

 the fact that " rays of light making very small angles 

 with each other do not separate perceptibly until 

 they have gone some distance." 



Professors Ayrton and Perry tested magic mirrors 

 by these rules, and found their phenomena in every 

 way to agree with these laws, and by the application 

 of lenses to intensify the results, fully established their 

 views on the subject. 



A. Tomlinson. 



TAMENESS OF A ROBIN. 



AMONGST the many instances of tameness in 

 wild birds coming within the ken of almost 

 every country resident, none recorded, have, I 

 imagine, surpassed the following. 



One day, during the past summer, I entered my 

 dining room to find, perched upon a book-shelf, a 

 friendly redbreast, who, now and again, favoured me 

 with a visit. Undisturbed by my entrance, from his 

 standpoint upon the Book of books, he contem- 

 plated, with great apparent interest, my proceedings. 

 Reflecting that books were not the most suitable 

 perches for birds, I opened wide the door, and in- 

 timated that, at that moment, his room was preferable 

 to his company. The hint was taken — instead, how- 

 ever, of making his exit through the open garden 

 door — as I expected — flitting gaily across the hall, 

 he entered the drawing-room. Here making himself 

 quite at home, upon a chiffonniere, my friendly visitor 

 disported himself, perkily, meanwhile, surveying his 

 host, and making minute examination of my knick- 

 knacks. 



But, lo ! suddenly all is changed, for, in the plate- 

 glass back he discovers, reflected, his robinship's 

 image, and in a very frenzy of rage precipitates 

 himself upon it, wildly beating the glass with his 

 wings, in his futile efforts to reach his supposed adver- 

 sary. A greater regard for my treasures even than 

 for his pugnacious birdship led me to interpose, and 

 chase him from the room. He was not, however, to 

 be thus summarily dismissed, for, alighting upon the 

 top of the open garden door, he eyed me knowingly, 

 utterly regardless of my ssh-ssh-sshs. 



