1885.] On Certain Errors in Lunar Observations. 
appears to be sympathetic or dependent. I am not impulsed 
01 impiessed by the thoughts or feelings of a foreign person, 
though I am cognizant of them through the medium above 
termed ethereal.” 
(To be continued). 
II. ON CERTAIN ERRORS IN LUNAR OBSERVA- 
TIONS HITHERTO UNKNOWN. 
By Major-General A. W. Drayson, late R.A., F.R.A.S. 
vjlj3)EF0RE chronometers had been constructed so as to 
|Jpp give an exact measure of time, the Lunar was the 
best means of obtaining a close approximation to 
Greenwich mean time, when the observer was in localities 
distant from Greenwich. It is possible that an accident 
may happen to a chronometer, and no accurate means other 
than a Lunar can be made use of to obtain Greenwich time. 
Observing the eclipses of Jupiter’s satellites may give an 
approximation to Greenwich time ; but this is not so accu- 
rate a method as the Lunar, unless the observer possess a 
large telescope, and this telescope is fixed on a stand. No 
navigator ought to be unacquainted with the method of 
measuring the altitudes, and lunar distances, and of working 
out the calculations. 
As a problem only, the Lunar is worth studying, as it 
presents some very neat and beautiful examples in Geometry, 
and affords an excellent test of the skill of an observer, in 
measuring altitudes and distances. 
I believe I can claim to have measured and calculated 
more Lunars than most observers, because, during the 
thirteen years that I had the superintendence of the Wool- 
wich Observatory, I instructed more than one hundred 
officers and many more cadets on this subject, and during 
some years I measured and worked out between three and 
four hundred lunars per year. 
Having the means of knowing Greenwich time to a second, 
