(meteorobs) Indication of ZHR in 1868.

[drobnock]

The following may give additional information on the development of the
use of Zenithal hourly Rate as used to describe the intensity of a given
meteor shower.

In a report for the British Association for the Advancement of Science,
August 1868 under  Committee Reports of Luminous Meteors 1867-68
(Glaisher,Greg,Brayley, Herschel,Brooke) the discussion was on the past
years observations and data collected. The topic of interest are the
brilliant fireballs observed. Included in the discussion (pp 407,
411-412)  is a summary of a Memoir (1867) of G. V. Schiaparelli  ( Notes
and reflections on the Astronomical Theory of Falling Stars.) Chapter 6,
discusses the value of  D, real meteor density per minute,  versus
observed density d.  A formula is given for a correction to the show the
actual number of observed meteors per minute,  if the observer were
observing the meteors at the zenith in their  location.

"Applying the shown formula to calculate the real density of the meteors
in the great shower of 13th and 14th of November 1866, from the
apparent  density d, (123 meteors per minute) as observed  at Greenwich,
..., the value of D, or real density of the stream for the observers of
the Greenwich, is found to be 171 meteors per minute. (p. 411)"

As noted earlier the 1860-1870  is a period for the acceptance of meteor
observations and the refinement of observations.

George John Drobnock