Bought a telescope to-day.

March 13. 

Bought a telescope to-day for eight dollars. 

Thoreau's Flute, Telescope, and a Copy of Wilson's Ornithology

Alfred Winslow Hosmer 1851 - 1903, Photographer

(Concord Free Public Library)

Best military spy glass with six slides, which shuts up to about same size, fifteen dollars, and very powerful. Saw the squares of achromatic glass from Paris which Clark uses; fifty-odd dollars apiece, the larger. 

My glass tried by Clark and approved.  

C. was making a glass for Amherst College.

H. D. Thoreau, Journal, March 13, 1854

Bought a telescope to-day for eight dollars. See April 10, 1854 ("I bought me a spy-glass some weeks since. I buy but few things, and those not till long after I begin to want them, so that when I do get them I am prepared to make a perfect use of them and extract their whole sweet"); April 23, 1854 ("I think I have got the worth of my glass now that it has revealed to me the white-headed eagle"); March 13, 1853 ("All enterprises must be self-supporting, must pay for themselves.")

See also March 14, 1854 (""Counted over forty robins with my glass in the meadow north of Sleepy Hollow , in the grass and on the snow ."); March 16, 1854 ("I see ducks afar , sailing on the meadow , leav- ing a long furrow in the water behind them . Watch them at leisure without scaring them , with my glass ; observe their free and undisturbed motions ."); March 21, 1854 ("River skimmed over at Willow Bay last night . Thought I should find ducks cornered up by the ice ; they get behind this hill for shelter . Saw what looked like clods of plowed meadow rising above the ice . Looked with glass and found it to be more than thirty black ducks asleep with their heads in [ sic ] their backs , motionless , and thin ice formed about them . "); March 22, 1854 ("Saw a small black duck with glass , — a dipper ( ? )"); April 2, 1854 ("Saw black ducks in water and on land . Can see their light throats a great way with my glass . They do not dive , but dip . "); April 3, 1854 ("April 3. Saw from window with glass seven ducks on meadow - water , only one or two conspicuously white , these , black heads , white throats and breasts and along sides , the rest of the ducks , brownish , probably young males and females . Probably the golden - eye . "); April 8, 1854 ("Saw a large bird sail along over the edge of Wheeler's cranberry meadow just below Fair Haven , which I at first thought a gull , but with my glass found it was a hawk and had a perfectly white head and tail and broad or blackish wings . It sailed and circled along over the low cliff , and the crows dived at it in the field of my glass , and I saw it well , both above and beneath , as it turned , and then it passed off to hover over the Cliffs at a greater height . It was undoubtedly a white- headed eagle . It was to the eye but a large hawk . "); April 23 1854 ("Saw my white - headed eagle again , first at the same place , the outlet of Fair Haven Pond . It was a fine sight , he is mainly — i . e . his wings and body black against the sky , and they contrast so strongly with his white head and tail . He was first flying low over the water ; then rose gradually and circled west- ward toward White Pond . Lying on the ground with my glass , I could watch him very easily , and by turns he gave me all possible views of himself . When I ob- served him edgewise I noticed that the tips of his wings curved upward slightly more , like a stereotyped the undulation . He rose very high at last , till I almost lost him in the clouds , circling or rather looping along west- е ward , high over river and wood and farm , effectually concealed in the sky . We who live this plodding life here below never know how many eagles fly over us . . . I Now I see him edgewise like a black ripple in the air , his white head still as ever turned to earth , and now he turns his under side to me , and I behold the full breadth of his broad black wings , some- what ragged at the edges . ") and Bill Uhrich: Thoreau a pioneer in watching rather than shooting birds

Alvan Clark of Cambridge Clark began to sell telescopes around 1850, and eventually became the premier telescope builder in the United States.

My glass tried by Clark and approved. In this journal entry for March 13 Thoreau roughly describes what is known as the "star test," still used to evaluate telescopes today.~ Thoreau Society Bulletin

Only a part of the object ( ? ) glass available . Bring the edge of the diaphragm against middle of the light , and your nail on object glass in line with these shows what is cut off . Sometimes may enlarge the hole in diaphragm . But , if you do so , you may have to enlarge the hole in diaphragm near small end , which must be exactly as large as the pencil of light there . As the diameter of the pencil is to the diameter of the available portion of the object glass , so is the power , so many times it magnifies . A good glass because the form of the blurred object is the same on each side of the focus , i . e . , shoved in or drawn out .