GUIDO HORN D'ARTURO
Born 13 Feb. 1879, Trieste; died 01 April 1967, Bologna.  Born Guido Horn. 
Graduated U. Vienna 1902.  Worked at observatories of Trieste, Catania, 
Turin, Bologna, Rome.  Trieste was under Austrian government, joined Italian 
army in WWI as Guido d'Arturo to avoid capture as deserter.  Research 
included positional astronomy, moving clusters, comets, solar eclipses, and 
history of astronomy; optics including geometric, instrumental, physiologic, 
& unusual optical instruments.  1920, director of observatory of Bologna U., 
directed its renovation, published in Pubblicazioni of B. U. through career.  
Built a branch of B.U. at Lojano, 2600 feet altitude, with a 60 cm Zeiss 
reflector, used by d'Arturo to study variable stars, globular clusters, 
planetary nebulae, distribution of nebulae.  Devised a method of measuring 
density of stellar tracks on photographic plates using diffraction.  Visual 
astronomy, elaborated the effect to vision of the suture of the eye lens, 
and the 'black drop' effect during transits.  1924, motion of eclipse shadow 
bands interpreted as images of sun formed by turbulent air cells in 
stratosphere; similar to stellar scintillation.  Studied projected image of 
sun from locations in N. & S. hemispheres, direction & intensity of ripples 
seen in solar limb correlated with direction of stratospheric winds, deduced 
to be from air cells at 13 km altitude.  Confirmed by study of stellar 
scintillation at Perkins Obs. circa 1950s.  Director of expedition to 
Somalia for eclipse of 14 Jan. 1926, photographed flash spectrum & 
prominences.

1932, researched multiple mirror telescopes, small spherical mirrors of 
hexagonal outline, laid on parabolic shell.  1935- 13 Feb. 1965, 12 
Pubblicazioni B.U. on these 'composite' mirrors, described design, progress, 
use in research, and optic theory of star images.  First design was fixed at 
vertical orientation, a one meter array of spherical glass tiles 
(trapezoidal outline, 10 cm radius) in a parabolic surface, used 
photographically with motor driven plate holder.  1935, first photographs, 
used strip of 10 mirrors.  1938, removed from teaching & director positions 
due to Jewish background.
After war, reinstated as director, new mirror began, an array of 20 cm 
diameter hexagonal glass tiles.  1950, two rings totaling 19 tiles were in 
place; 1952, three rings and 37 tiles; 1953, four rings totaling 61 tiles; 
making a mirror of 1.8 meters diameter and 10.4 meters focal length, f6.  
Difficulty in making tiles of identical focal length necessitated 
fabrication of many more than necessary and using only a few; and the radii 
of curvature could be held to only plus or minus 2 cm (from the 20.8 m RoC 
of the mirror).

The mirror was fixed on a marble slab, a zenith telescope, situated four 
floors beneath the roof of Bologna Observatory; all four very solid floors 
(from 1711) had to be pierced before use.  The telescope was directly 
attached to this tower (and was used to study the building's oscillations), 
no control over ventilation was available, and the site is at the center of 
the city of one half million population.  Due to limited funding, no use was 
made of Pyrex, Invar, or other superior materials.

Parabolization and collimation was accomplished by setting each ring of 
tiles slightly higher than the next inner ring, using three adjusting screws 
behind each mirror, raising & tilting it.  Illuminated cross hairs were 
placed at the center of curvature of the central mirror, and viewed through 
a collimating telescope, along with their reflection.  When the wires were 
in place, their image coincided with their position.  Another mirror was 
adjusted until its image coincided with the central mirror, and the 
remaining 60 mirrors likewise adjusted, taking about 90 minutes.

The telescope photographed a 1.3 degree wide strip of sky at 44.5 degrees N. 
latitude.  With G.B. Lacchini, it was mostly used to photograph many new 
variable stars of mag 14-16, obtaining elements & light curves; the faintest 
stars recorded were mag 18.5.  Exposure time was limited to 6.5 minutes, 
when the sliding plateholder moved off axis.  The largest plate used was 9 
cm x 24 cm, imaging 3 min. RA by 80 min dec.  Many thousands of plates, 
considered acceptably coma-free, were made; and many new variables were 
discovered.
There were plans for a series of these telescopes at different latitudes; 
also for larger models built into craters and bowls in the earth.
The telescope was not used after Horn D'Arturo's retirement in 1954. 

Also designed a conic lens, to be used like a prism lens.  Spectra of stars 
show concentric spectral lines; circular lines for stars on axis, others are 
fourth order curves.  135 degree field of view, placing camera & conic lens 
vertically, used for spectra of meteors.

Founder & editor of Coelum (popular astronomy magazine), and an editor of 
Piccola enciclopedia astronomica.

There is a Guido Horn D'Arturo Observatory, C.P. 1630, 40100 Bologna AD, at 
Tizzano, near Bologna; and a new Guido Horn d'Arturo library of astronomy in 
Bologna.

Sources. 

Abetti, Giorgio. Guido Horn d'Arturo. Dictionary of Scientific Biography. 
Charles Gillispie, ed.  New York: Scribner, 1970--.

Barbieri, Cesare. Guido Horn D'Arturo and his Tessellated Mirror. Optical 
Sciences Center Newsletter vol. 6, 1972. pp20-1.

(Guido Horn d'Arturo, astronomo e uomo di cultura.) Bologna: Cooperativa 
Libraria Universitaria Editrice Bologna, 1994.

Ingalls, Albert. Scientific American 184 (January 1951) 60-3.

Jacchia, Luigi. An Italian Astronomer. Sky & Telescope, v34 #2, Aug. 1967, 
p93.

Jacchia, Luigi. Forefathers of the MMT. Sky & Telescope, v55 #2, Feb. 1978, 
pp100-2. (photos).

(Journal of the British Astronomcial Association 63 (January, 1953) 71-4.)

Zuccoli, Marina and Fabrizio Bonoli, ed. Guido Horn d'Arturo e lo specchio a 
tasselli. Bologna: Cooperativa Libraria Universitaria Editrice Bologna, 
1999. 103p. ISBN 88-491-1292-0. paperback, 240x170mm. 9 papers by d'Arturo 
on multiple mirror telescopes, 1932-1966, introd., short bio.