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seen eight years later. In each case there is the palpable sub- 
stitution of an ideal picture for the supposed reality ; in each case 
the technical explanation is opposed to the narrative itself as well 
as to the known physical laws ; it being noteworthy that, in both, the 
concealed part of the object is represented as always visible ; and in 
such case the obvious absurdity of the substitutions shows clearly 
the absence of any conscious intention to deceive. Mr. Vince has 
told, in perfect good faith, the impressions on his own mind; 
impressions so strong as to have shut out every consideration of 
probability or of possibility, and to have completely overpowered 
his better judgment. The mastery over his mind, acquired by this 
delusion, is well exemplified by the proposal seriously made, that, 
on the recurrence of such a phenomenon, a ship be sent out provided 
with barometers on deck and at the mast head, to ascertain the 
difference of pressure. He expected wind enough to carry the ship 
to sea, forgetting that perfect calm is essential to the stratification ; 
he forgot too that no then existing barometer could be accurately 
read on ship-board. 
The dominant idea was in both cases that of the great curvature 
of the rays of light. In his Complete System of Astronomy , 1823, 
Vince shows that the curvature is only one-seventh part of the 
curvature of the earth. It is pleasant to think that these early 
occasional illusions had passed away, to leave his mind clear for the 
performance of such great and good work in furtherance of Astro- 
nomical Science. 
5. On a Case of Dyspeptic Vertigo. 
By Professor Crum Brown. 
The dyspepsia was, as far as I know, of a very ordinary kind. It 
began with loss of appetite, discomfort after meals, and general 
sense of weakness and uselessness. Then came a crisis. Waking 
in the middle of the night with pain and nausea, an hour or two 
of this, thorough evacuation of the stomach, great discomfort next 
day, and then no symptom of any thing wrong as long as I adhered 
to the diet which experience soon led me to, viz., very simple food 
and very little of it. To this I adhered for about four weeks. 
How and then, perhaps three times altogether, feeling quite well, I 
ventured to eat like other people, and was at once taught by 
