CARER 5 { April, 
IJ, ASTRONOMY. 
(Including the Proceedings of the Royal Astronomical Sociely.) 
Proressor Grant, F.R.S., of the Glasgow Observatory, has been 
for some time past engaged in the determination of the difference 
of longitude between the Observatories of Greenwich and Glasgow 
by galvanic signals. The method adopted was that of double 
registration, which has been practised so successfully in the United 
States of America, and more recently in Europe. ‘The principle of 
this method is extremely simple. When a star passes each of the 
successive wires of the transit telescope of the more eastern of the 
two Observatories, the observer, by tapping a key with his finger, 
completes a galvanic circuit, and the instant of transit is recorded 
on the chronographic apparatus of the Observatory; but the 
galvanic current, instead of going to earth, is made to pass along 
the line wire to the recording apparatus of the distant Observatory, 
upon which also the instant of transit is in the same way recorded. 
A process exactly similar is repeated when the star comes to the 
meridian of the more western Observatory, the instant of transit 
being registered on both chronographic apparatuses by the same 
completion of the galvanic circuit. In this manner each signalling 
star supplies two pairs of recorded times of transit, a comparison of 
the individual values of which gives two distinct results, the one 
indicating the difference of longitude between the two Observatories, 
the other assigning a value of the time occupied by the galvanic 
current in its passage from the one Observatory to the other. The 
period of operations extended from April 28 in the past year to 
May 26. ‘The stars selected for observation amounted in number 
to twenty-eight, and were arranged in four groups of seven stars 
each, and in such a manner that when the last star of any group 
had passed before the telescope of the Glasgow Transit Circle, 
which was the more western instrument, the first star of the 
succeeding group was nearly about to commence its passage over 
the wires of the Greenwich or more eastern instrument. 
The weather on the whole was not favourable for simultaneous 
observations at both Observatories during the period of four weeks 
over which the operations extended. In several instances observa- 
tions were made at Greenwich which could not be responded to from 
Glasgow, and in one or two instances the converse of this happened. 
On four nights, however— May 1, May 2, May 22, and May 25— 
the sky was favourable for observation at both Observatories, and it 
is upon the results obtained on those nights that the determination 
of the difference of longitude is exclusively based. 
