EXPLANATION OF PHENOMENA. 221 



to the spectral image, especially if they had seen it 

 gradually decay, and finally disappear on the still and 

 unbroken surface of the lake. No similar fact had been 

 previously observed, and there were no circumstances 

 in the case to have excited the suspicion that it was 

 the spectre of a real vessel produced by unequal refrac- 

 tion. 



The spectre of the Brocken and other phenomena of 

 the same kind have essentially a different origin from those 

 which arise from unequal refraction. They are merely 

 shadows of the observer projected on dense vapour or thin 

 fleecy clouds, which have the power of reflecting much 

 light. They are seen most frequently at sunrise, because 

 it is at that time that the vapours and clouds necessary 

 for their production are most likely to be generated ; and 

 they can be seen only when the sun is throwing his rays 

 horizontally, because the shadow of the observer would 

 otherwise be thrown either up in the air, or down upon 

 the ground. If there are two persons looking at the 

 phenomenon, as when M. Haue and the landlord saw it 

 together, each observer will see his own image most 

 distinctly, and the head will be more distinct than the 

 rest of the figure, because the rays of the sun will be 

 inore copiously reflected at a perpendicular incidence ; 

 and as from this cause the light reflected from the vapour 

 or cloud becomes fainter farther from the shadow, the 

 appearance of a halo round the head of the observer is 

 frequently visible. M. Haue mentions the extraordinary 

 circumstance of the two spectres of him and the land- 

 lord being joined by a third figure, but he unfortunately 

 does not inform us which of the two figures was doubled, 

 for it is impossible that a person could have joined their 

 party unobserved. It is very probable that the new 

 spectre forms a natural addition to the group, as we have 

 represented it in Fig. 30, and if this was the case, it could 



