SAMUEL PIERPONT LANGLEY. 
9 
that intimate knowledge of French history to which I shall 
allude later on. 
The question of the personal error or personal equation, 
which has attracted so many astronomers, also had his atten- 
tion, and he described in a communication to the American 
Journal of Science in 1877, a machine whereby this personal 
error could be entirely eliminated. 
In 1878 he took charge of a party sent out by the United 
States to witness the total eclipse of that year from Pike’s 
peak, at an elevation of 14,000 feet, and, besides the scien- 
tific memoirs which resulted therefrom, and through which 
he was able to follow the corona to an hitherto unsuspected 
distance from the sun, he wrote pleasant, chatty letters de- 
scribing the more personal side of the work of the party. 
In the winter of 1878, during the course of a visit to 
Europe, he spent some time upon Mt. Etna, and made ob- 
servations there which resulted in the production of scien- 
tific papers and a very interesting article entitled “Winter- 
ing on Etna,” which was contributed to the Atlantic 
Monthly. 
In 1881, through the generosity of the citizens of Pitts- 
burg and with the cooperation of the United States Signal 
Service, he conducted an expedition to Mt. Whitney, to 
which reference has already been made. 
Mr. Langley’s general reputation shortly after this be- 
came greatly enhanced by a series of popular lectures deliv- 
ered at the Lowell Institute and at the Peabody Institute at 
Baltimore, afterward published in the Century Magazine, 
and later still in the form of a book, which has gone through 
several editions, under the title of “The New Astronomy.” 
These lectures and this work set clearly before educated 
people the results of his own labors and of others in that 
branch of astronomy which, dealing not with the questions 
of longitude and latitude, or the discovery of planets, aster- 
oids, or comets, or the other problems of the older astron- 
omers, had to do with the physics of the heavenly bodies; 
the study through patient observation and numerous in- 
2— Bull. Phil. Soc., Wash., Vol. 15. 
