419 
SCIENTIFIC SUMMARY. 
QUARTERLY RETROSPECT. 
ASTRONOMY. 
Difference of Longitude between Greenwich and Valentia. — The Astronomer 
Royal, under whose superintendence this inquiry was determined in 1845, 
by the transmission of chronometers, has recently verified it by signalling 
with the electric telegraph, when almost exactly the same result was 
arrived at. It is strange that there should have been so great a difference 
in the result found by these two processes in the case of Cambridge and 
Greenwich (a comparatively short distance), namely, by chronometers in 
1828 and by telegraph in 1853 ; but probably greater precautions had been 
taken in the carriage of the chronometers in the Valentia expedition. It 
is stated that the current took one-tenth of a second to traverse the 800 
miles of wire. 
This is, however, only a preparatory step, before endeavouring to deter- 
mine the length of the arc between the most western point of Europe 
(Valentia, in Ireland), and the town of Orsk, in the east of Russia. By com- 
bining the numerous old and some new triangulations, which it will be 
necessary to take, it is intended to measure this in yards. The distance 
between the two stations is seventy degrees , so it may be imagined how 
many units of that popular cloth-measure shall be swallowed by this men- 
suration. The differences of time at the east and west points will be 
obtained, when available, by the telegraph. 
The Elchies Refractor. — In our last summary we gave Professor Smyth’s 
experiences with this instrument (11-inch aperture), showing the existence 
of many small stars whose places had not been previously recorded. 
Mr. Dawes has, however, been able to detect many, if not all, of those 
with a telescope of 8J inches aperture. He points out that “ the most 
valuable property in a telescope is undoubtedly a fine sharp definition 
and concludes that an object-glass of 11 inches will show a star whose 
magnitude is about 12 J of Struve’s scale, or 18| of Sir J. Herschell’s. 
Mr. Knott has also been able to detect all the stars of 222 Piazzi I., the 
star B., missed by Professor Smyth, being readily seen. 
Variable Stars. — A proposal has been made for establishing an asso- 
ciation for the systematic observation of variable stars. A similar asso- 
ciation was formed some sixty years since for the detection of the smaller 
