(3) 
Appendix. 373 
meridian observations, the experience of the past year at Greenwich 
Observatory (where observations are carried on as continuously 
through the 24 hours as at any other observatory) shows that the 
whole of the astronomical day can be introduced very easily and 
with decided advantage on the whole. (4) In the case of extra- 
meridian observations, the observer usually finds it convenient to 
work in the earlier hours of the night, so that little or no incon- 
venience would result from a change of date at midnight. Dis- 
coverers of comets and observers of meteors, who observe in the 
early morning, often use civil reckoning, and mistakes of date 
have, on several occasions within my own knowledge, resulted 
from the existence of two different modes of counting time. (5) For 
spectroscopic and photographic observations of the sun, it is now 
recognized that the day should be reckoned from midnight, and 
the same reckoning would naturally be used by the observer when 
he takes spectroscopic and photographic observations at night, and 
also in determinations of the places of comets, stars, etc., which he 
may make in connection with his spectroscopic observations. It 
seems absurd to expect the same observer to change his system of 
reckoning mean solar time according to the class of observations 
he is making at the moment. (6) The proposal to include in the 
routine work of an observatory, photography of the stars, as. well 
as of the sun, will further increase the difficulty of maintaining 
a distinction as regards ‘time-reckoning between the various classes 
of astronomical observations. (7) At many observatories, magneti- 
cal and meteorological observations are carried on concurrently 
with astronomical observations, and it is admitted that for the two 
former classes the day commencing at midnight should be used. 
(8) For the distribution of the time to the public, a work which is 
undertaken by many observatories, the civil day would be used. 
(9) Thus civil reckoning commencing at midnight must be used 
for solar, magnetical, and meteorological observations, and also for 
the distribution of time to the different systems of mean solar 
clocks, differing by 12 hours, in the same observatory—a circum- 
stance likely to lead to intolerable confusion. (10) As regards the 
supposed discontinuity which would arise from the change in the 
Nautical Almanac, the difference of time-reckoning is precisely 
similar to that which would have to be taken into account in the 
comparison of Greenwich observations with those made at any 
other observatory. The astronomical calculator is in the habit 
under the present system of allowing for the difference in time- 
reckoning between different observatories, and his task would be 
greatly simplified if he had only to deal with the universal time.— 
Report to the Trustees of Greenwich Observatory, by W. H. M. Christie, 
M.A., LL.D., Astronomer Royal of England. 
