44.0 Scientific Proceedings, Royal Dublin Society. 
glass, so that the image of a point on the latter is also found next 
the wire, and can also be observed while the tube is turned. Thus 
the flexure of the two halves of the tube is determined. The 
effect of a displacement of the small lens is eliminated by com- 
paring the image of the wire with that of a point in one of the 
pivots, the image of which is reflected from a plane surface on one 
side of the lens. 
Another method of determining flexure has been proposed by 
Nobile (A.N. 2281). A small telescope is placed on the axis of 
the transit instrument, parallel to the line through the pivots, 
the object-glass being towards the tube. A small lamp and a 
diaphragm send a pencil of parallel rays towards the cone; a 
small prism on the latter throws the rays to one side of the 
object-glass, from thence to a small prism on the centre of the 
latter, from which the pencil of rays is sent down the tube and 
appears in the eye-piece as an artificial star. The motion of 
this star while the tube is turned in zenith distance gives the 
means of finding the flexure. 
3. Celestial Mechanics. 
At the January meeting of the R.A.S., Mr. Neison read a paper 
“On the General Solution of the problem of Disturbed Elliptic 
Motion.” The aim of this paper is to show that by choosing 
suitable variables, and by transforming the differential equations 
in a proper manner, it will be possible to obtain a complete and 
very elegant general solution of the problem of disturbed elliptic 
motion ; that is to say, a solution which is so far general, that it 
becomes possible to find a very simple expression for the pertur- 
bations to the mth order of the disturbing forces, and be indepen- 
dent of any particular values of the elements. In practice, 
however, this method involves a great amount of computation. 
Volume XLIV. of the “Memoirs of the Royal Astronomical 
Society ” contains a memoir by Mr. Neison “On a General Method 
of treating the Lunar Theory.” This memoir gives the theo- 
retical foundation on which Mr. Neison has based a complete 
analytical development of the lunar theory. Although it involves 
no new principle, being in fact no other than Pontécoulant’s, the 
method by which the development is being effected consists of 
