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room into hobgoblins. Similarly a strong desire of some result, 
such as success in a lottery, causes us by continual representation 
of our good luck to over estimate our chances. Fear acts in the 
same way. By producing a very vivid image of the calamity we 
are led to believe in its certain occurrence. Many apparent 
suicides from precipitous positions are probably due to the mind 
being completely upset by the vivid representation of the danger 
of an accident. 
The second chief cause of illusions is to be found in the 
derangement of the sense-organ or nervous system. The 
deceptions of colour-blindness, and of subjections, auditory and 
gastatory sensations are examples. Even apparent tactual 
sensations of temperature and pressure may have their origin in 
this source. 
An abnormal condition of the atmosphere, or of whatever 
medium connects the sense-organ with the perceived object may 
produce serious illusions. Preceptions of sight and sound are, 
in the main, inferences from present appearances based on past 
experience. Neither the eye nor the ear, for instance, can of 
themselves directly apprehend distance. The intensity of the 
sensation, and its vague or definite character as compared with 
former experiences, lead us to localise an object at a particular 
distance. A mountain seems close at hand in clear weather, 
and a boy obscurely apprehended in a fog appears to be a 
full-grown man. An unfurnished room looks much smaller than 
it really is, because the customary articles are not present to 
impress on us, the capacity of the space, similarly the sun and 
moon seem larger when near the horizon, owing to the 
intervening trees, hills, &c., causing us to realise better the 
greatness of the distance. 
Dreams have always been a subject of interest, and philosophers 
from the earliest times have made efforts to explain them. The 
most remarkable work on Dreams among ancient writers was 
Aristotle’s treatise on the subject. Nearly all of us have had 
experience of dreams. A dream is an illusion during sleep in 
which the acts of the imagination are taken for reality. During 
sleep the activity of the external senses falls into abeyance, 
volitional control over the course of thought ceases; the power 
of reflexion and comparison is suspended ;_ and the fancy of the 
dreamer moves along automatically under the guidance of associa- 
tion. Consideration of these circumstances helps to partially 
account for the peculiar features of the dream. Its chief charac- 
teristics are its seeming reality, its incoherence and extravagance, 
its possession of a certain coherence amid this inconsistency, and 
the exaggeration of actual impresions. 
The apparent reality of the dream is in great part a consequence 
of the cessation of the action of the external senses. The images 
