Grinnell College Physics Museum

Search

105 items

Calculator

High-Speed Adding Calculator

Calculator

High-Speed Adding Calculator

Transit Telescope

A Transit Telescope is the basic instrument for determining time by stars. It is fixed such that the instrument rotates on its axis in a north-south plane.1 An observer using the transit telescope watches a chosen star pass across the cross-hairs. These time measurements probably provided time base for the Haish telescope in the Goodnow observatory and did provide time for the Rock Island railroad. This Fauth Transit Telescope was purchased by the college in 1888 for a concessional price of $550.   The transit telescope (in Noyce Hall foyer), chronograph (in display case F2), astronomical Seth Thomas clocks (in Kistle Science Library), and micrometer (in case F2) were purchases requested by Samuel J. Buck following the construction of the Goodnow observatory with its Haish telescope. “If a man makes you a present of a fine horse, immediately you begin looking about for a saddle and bridle, harness, carriage and sleigh in order to make use of the horse,” The transit telescope is the basic instrument for determining time by stars. The axis of a transit telescope is fixed in the east west direction so that when the instrument moves, it moves only up and down in a north-south plane. This one was mounted on a Y shaped metal base and located in the brick transit house just East of Goodnow. It was reported to have an objective with aperture of 3 inches and three eye pieces, a direct, diagonal, and a nadir, with approximate powers of 50, 100, and 30, respectively.  An observer would watch a chosen star pass across the cross-hairs. The time between one passage of a star and the next is one sidereal day. The interval between two successive passages of the sun past some fixed point in the sky, such as the meridian, is one solar day, and it is 3 minutes 56 seconds longer than the sidereal day. Because the observations of stars are made at night, the cross-hairs must be illuminated. The cross-hairs are in the center of the telescope tube, and a window at each end of the support admitted light from a kerosene lamp to make the cross-hairs visible. From a knowledge of the longitude of the observatory and the location in the sky of a particular star, one can calculate precisely the time at which that star passes the local meridian. If the passage is observed with the transit telescope, the derived time can be used to set a clock or, more likely, produce a correction to be applied to the clock’s reading. It is easier to use corrections than to set clocks frequently.

Wang Electronics Package

Transistorized electronics package for Wang calculator system

IBM Punch Card Fortran Code

Used by Charlie Duke for non-linear least-squares curve fitting during the 1960's. Fortran Program used at ISU computer.

Polaroid Camera

model 360 (with te_170 and te_171)

Chronograph

The chronograph was used in conjuction with a transit telescope to make a correction to a clock. The drum was covered with a sheet of paper, and a pen-holding mechanism, now lost, moved along the length of the drum as the drum rotated. The pen made a continuous line on the paper. The pen mechanism was connected to a clock which put out an electrical pulse every second, and those pulses made jogs in the line. An observer at a transit telescope watched for the passage of a star through the meridian, and when the star crossed the cross-hairs of the telescope, the observer closed a switch which produced a different sort of jog in the line. It was then possible to determine within a small fraction of a second what the clock read when the star crossed the meridian. The drum was turned by a spring motor, and the governor to control the speed is in the upper right of the picture. This was part of the equipment in the Grinnell College observatory in the late 1800s.