  Sometimes arguments that preceded recognition of non-Euclidean (Lobachevsky)
geometry are represented in a simplified `black and white' pattern:
`conservators made nonsense of genius'. Although there is something in this
point of view, the real situation was more complicated, and up to some time
there were decent grounds for not recognizing the importance of the new theory.
We try to explain why non-Euclidean geometry was not recognized at once. We
show how important for such recognition was discovery of applications of the
new geometry.
  These reflections have practical importance for modern mathematics because
they are related to the question: how a mathematician should choose directions
for research?
