Recorder
In the 19th century, devices were called recording apparatus by means of which observations of natural phenomena were recorded at the same time as the corresponding observation times.
Electromagnetic recorders were widespread, the simplest example of which is the chronograph (an electro-magnetically registering clock ), and their use achieved great accuracy in determining astronomical length and time.
Other astro-geodetic recording devices are the electrical contacts on pendulum clocks introduced in the 19th century or the Sterneck pendulum apparatus for measuring gravity.
Electromagnetic recording apparatus
With every stroke of the pendulum of an astronomical clock, a galvanic chain is closed, in whose closing arc a writing device similar to the Morschen telegraph is switched on; the pen of the latter marks a point with every stroke of a second on a strip of paper moved by a clockwork at a constant speed.
In addition to this writing device, which marks the individual seconds, a second similar device is attached, the pen of which is pressed against the paper strip as soon as the observer closes a galvanic current belonging to the second device by pressing a button.
In this way, in addition to the series of second points, a series of observation points is obtained on the paper strip. Should z. If, for example, the moment of the meridian passage of a star is determined, the observer looks through the midday tube and puts his finger on the key, which he depresses as soon as the star appears on the crosshairs.
If the observation point is now between two seconds, the compass can be used to measure its distance from the previous second and then determine how many tenths and hundredths of a second are added to the previous second.
Instead of the paper strip a metal cylinder blackened with soot is used, which is rotated by a clockwork at constant speed around its horizontal axis and at the same time, by means of a screw thread cut on this axis, is pushed in the direction of the axis; the seconds dots therefore lie on a flat helical line wound around the cylinder (cf. Lamont, description of the new instruments and apparatus used at the Munich observatory , Munich 1851).
Self-registering apparatus
Self-registering devices, which continuously record the weather observations, were of great importance for meteorology . From the large number of these instruments, the Wagebarograph, constructed by Rudolf Fuess according to Adolf Sprung's principle, should be highlighted as an example.
Photographic recorders
Yet another principle has been used in photographic recorders, such as the thermograph or the photo psychrograph .