| US 7,555,840 B2 | ||
| Omni-directional lens in sundials and solar compasses | ||
| Chengjun Julian Chen, White Plains, N.Y. (US) | ||
| Assigned to The Trustees of Columbia University in the City of New York, New York, N.Y. (US) | ||
| Filed on Aug. 17, 2007, as Appl. No. 11/840,428. | ||
| Prior Publication US 2009/0044417 A1, Feb. 19, 2009 | ||
| Int. Cl. G04B 49/00 (2006.01); G01C 17/34 (2006.01) | ||
| U.S. Cl. 33—269 [33/270] | 12 Claims |
| 1. A sundial, said sundial comprising:
an omni-directional lens including at least two concentric spherical components, said at least two concentric spherical components
including a transparent outer sphere having a radius R1 and an index of refraction n1 and a transparent inner sphere having a radius R2 and an index of refraction n2; and
a replaceable panel positioned adjacent said omni-directional lens, said replaceable panel being selected from two replaceable
panels, each of said two replaceable panels having a semi-cylindrical shape and a surface having marks of date and time thereon,
a first one of said two replaceable panels including marks of date and time for a first part of a year and a second one of
said two replaceable panels including marks of date and time for a second part of the year;
wherein R1, n1, R2, and n2 are selected so that a parallel beam of sunlight impinging on said omni-directional lens will converge to a sharp spot of
light on said replaceable panel thereby indicating a time of a day and a day of a year.
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