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The Practical Astronomer: Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomyDick, Thomas

Science

The Practical Astronomer: Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy

Name: The Practical Astronomer: Comprising illustrations of light and colours--practical descriptions of all kinds of telescopes--the use of the equatorial-transit--circular, and other astronomical instruments, a particular account of the Earl of Rosse's large telescopes, and other topics connected with astronomy
Author: Dick, Thomas

Dick, Thomas

Astronomical instruments; Astronomy; Telescopes

-----------------------------------------+-+----------------------------------------
          NEWTONIAN TELESCOPES.            | |       GREGORIAN REFLECTORS.
  --------+---------+----------+-----------+ +--------+---------+----------+----------
  Diameter| Focal   | Price of | Price of  | |Diameter| Focal   | Price of | Price of
  in      | length  | Mirrors  | telescope | |in      | length  | Mirrors  | telescope
  inches. | in feet.| alone.   | complete  | |inches. | in feet.| alone.   | complete
          |         |          | without   | |        |         |          | without
          |         |          | stand.    | |        |         |          | stand.
  --------+---------+----------+-----------+ +--------+---------+----------+----------
          |         |  £    s. |  £    s.  | |        |         |  £    s. |  £    s.
          |         |          |           | |    6   |    3    |  17   10 |  25    0
          |         |          |           | |        |         |          |
      7   |    7    |  17   10 |  27   10  | |    7   |    3    |  25    0 |  34    0
          |         |          |           | |        |         |          |
      9   |   10    |  25    0 |  40    0  | |    9   |   4-1/2 |  35    0 |  50    0
          |         |          |           | |        |         |          |
     12   |   12    |  60    0 |  90    0  | |   12   |    7    |  70    0 | 100    0
          |         |          |           | |        |         |          |
     15   |   15    | 120    0 | 170    0  | |   15   |    9    | 150    0 | 200    0
          |         |          |           | |        |         |          |
     18   |   18    | 200    0 | 260    0  | |   18   |   12    | 240    0 | 300    0


ON THE EYE-PIECES OF TELESCOPES.

Although the performance of telescopes chiefly depends on the goodness
of the object-glass, or the object-speculum of the instrument, yet it
is of considerable importance, in order to distinct vision, and to
obtain a large and uniformly distinct field of view, that the eye-piece
be properly constructed. The different kinds of eye-pieces may be
arranged into two general divisions--_Astronomical_ and _terrestrial_.

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