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‘The largest of all the Deinosaurs was the Atlantisaurus lately 
discovered in Western America. Its length is believed to have 
been about 100 feet, and quite as bulky asa whale. Its thigh 
bone measures seven feet long ; its shoulder blade five feet, and 
one of its ribs 14 feet in length. A number of diagrams _ 
representing these reptiles were exhibited and fully described. 
ILLUSIONS AND DREAMS. 
By REV. FATHER MAHER, S.J., M.A. 
February 17th, 1891. 
The subject of ‘Dreams and Illusions’ has possessed 
great attraction for mankind from the very beginning. The 
investigation of these phenomena belongs to the science of 
Psychology. The questions of this science, though at a 
disadvantage on some grounds for treatment in a popular leciure, 
have at all events this much in their favour that they are, as a 
rule, of considerable interest, and also that they are capable of 
being studied by all men without the employment of any 
costly instruments—our own mind furnishing the laboratory, 
observatory, and all other requisite materials. 
An Illusion is an error or mistake, springing from what 
appears to be an immediate act of perception. It is thus 
distinguished from a Fallacy, which is an act of false reasoning. 
A Hallucination is an extreme form of Illusion. [Illusions may 
be divided into three great classes according to their causes. 
These causes lie either in the mind itself, in the bodily organism, 
or in the surrounding medium which connects the organism 
with the object perceived. The chief mental source of illusion 
is the imagination. Imagination plays an important part in 
normal perception and whatever excites it tends to render us 
liable to error. The chief mental states which stimulate the 
imagination into this over sensitive condition are expectation, 
desire and fear. Physiologically, the reason why vivid imagination 
leads to an illusory perception probably consists in the fact that 
the same portion of the brain is instrumental in the actual 
apprehension of an object and in the imaginary representation 
of it. A lively expectation of some event stimulates the fancy 
to form a vivid representation of it, and the brain being put in a 
state very much akin to that of real perception an illusion is the 
result. Listening to ghost stories before going to bed thus 
causes children to interpret the various objects in a darksome 
