Intelligence and Miscellaneous Articles. 



333 



bright 



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i-ges — those of two petroleum-lamps and one stearine 

 candle. As tobacco was being smoked in the room, I at first be- 

 lieved that the smoke had produced a similar phenomenon as slightly 

 moist air when it forms a halo round the moon or the sun, and that 

 in consequence of this the appearance was seen. I could not, how- 

 ever, perceive those halos round the flames, either in the looking- 

 glass or in the air. Abandoning the attempt to fathom the cause, 

 I occupied myself with the phenomenon itself, and perfectly recog- 

 nized it as a phenomenon of interference, because the streaks widened 

 as the angle of reflection increased. In the observation the flame- 

 images and the image of the eye had the following position : — 



A is the image of the eye, L y that 

 of the petroleum-flame before the 

 looking-glass, L„ that of a second 

 petroleum-flame at a greater dis- 

 tance, and L //; the image of the 

 candle burning on the table. The 

 interference-streaks at L , and L if/ 

 are represented in their situation. 

 As the phenomenon was observed in 

 a public place, w T here there were 

 many other glasses and lights, I 

 could not pursue the matter further ; 



but I resolved to repeat the experiment at home or in my study. 

 To this end, I placed opposite to the looking-glass in my room, at 

 about 6 metres distance, a petroleum-lamp ; I then took a stearine 

 candle in my hand, and so endeavoured to get the position which I 

 had had in the first observation. After looking from several differ- 

 ent points, and shifting the candle several times, I at length re- 

 marked faint streaks round my chin ; on further moving backwards 

 and forwards, the streaks were very beautifully developed, but not 

 so brilliant as on the first occasion. I now noted the 

 position. L / was the light of the petroleum-lamp, L /# 

 that of the candle, and A the eye (of course seen in the 

 glass). The streaks attained the greatest intensity 

 when Jj u was situated exactly under L , and A was to 

 be seen a little sidewards between the two. The streaks 

 widened out above L /; — not nearly as about a slit, but 

 quite uniformly around the flame, so that it seemed to 

 have no further influence on the streaks than to illumi- 

 nate them. The flames were now left in their position, the glass 

 taken down and carefully wiped and hung up again in the same 

 place. The streaks were again visible. I had then carefully to in- 

 vestigate whether dampness adhering to the glass, or particles of 

 dust, called forth the phenomenon. ; for I could not derive it from 

 the laws of refraction and reflection in the clean mirror. I next 

 dusted the mirror with lycopodium in such manner that around the 

 light-images splendid halos appeared. The marked position was 

 then taken, from which gorgeous interference-streaks were to be 

 seen ; nay, they arose not merely around the lower, but also around 



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