SOLAR RESEARCHES BY JANSSEN—PLUVINEL. 251 
theory of the sun. He knew that it is more useful to gather together 
observations than to build theories upon facts insufficiently dem- 
onstrated. But we must not conclude that the mind of Janssen was 
indifferent to speculation. In a number of his writings is found a 
depth of reasoning which gives evidence of his care in going to the 
very roots of matters. 
Born in 1824, Janssen did not devote himself completely to science 
until toward 1860, at the age of 36, but his scientific career was, 
nevertheless, as long as that of many scientists, for he retained until 
late all his faculties for work and died on the 23d of last December, 
after having reached his eighty-fourth year. 
