438 
ROBERT STANTON AVERY. 
tion, he was called to settle up the estate, and for seven years 
he worked on the farm, taught school during the fall, and 
continued his studies in the languages and higher mathe¬ 
matics and their application to the physical sciences, par¬ 
ticularly to light. During these years he made some scien¬ 
tific investigations, and constructed a reflecting telescope over 
five feet long. The speculum metal for the mirror was made 
and cast by him and then ground into shape and polished 
with such success that the instrument had a very fair defini¬ 
tion. He made an equatorial mounting, with graduated 
arcs, which enabled him to roughly estimate angular dis¬ 
tances. In the course of time the mirror became dull and 
covered with dust from lack of use, but he retained the in¬ 
strument to the close of his life and often spoke of it as 
having given him much pleasure and instruction. 
In October, 1853, he accepted a position on the United 
States Coast Survey. He came well prepared for his new 
duties, and it was not long before he attracted the attention 
of the superintendent, Prof. A. D. Bache, who selected him as 
special computer to carry out his plans for the reduction and 
prediction of tides. Some of these calculations were long 
and tedious, requiring many months of hard work. For in¬ 
stance, on one occasion he had more than 700 conditional 
equations, each containing 23 unknown quantities, for which 
he had to obtain the most probable values by the method of 
least squares. He computed the occupations of the larger 
stars of the Pleiades, the principal object being the correc¬ 
tion of the tables of the moon’s motions and the improve¬ 
ment of terrestrial longitudes. He was promoted from time 
to time as he proved his fitness, until after twelve years of 
work he was made chief of the tidal division of the Survey. 
He held that position for more than twenty years, when, ' 
owing to failing health and advancing years, at the age of 
77 he resigned, on September 30,1885, having spent 32 con¬ 
secutive years in the service. He was a painstaking and 
accurate computer, with good administrative abilities, and 
was especially successful in directing the labors of others, 
