XVI 
FIFTH REPORT— 1835 . 
provided the French Government agree to this proposition, the 
sum of 500/. be placed at the disposal of a Committee, to be 
hereafter nominated by the Council, for the purpose of procuring 
the duplicate reduction which is necessary to ensure accuracy*. 
3. That the difference of meridians between the Observatories 
of Greenwich, Cambridge, Oxford, Edinburgh, Dublin, and 
Armagh, should be determined by means of chronometers, or 
by signals, or by both methods. 
4. That it is desirable that the constant of lunar notation 
should be deduced from observations made with the mural circle 
at Greenwich, and that the sum of 100/. be appropriated to this 
purpose, under the direction of Sir T. Brisbane, Rev. Dr. Robin¬ 
son, and Mr. Baily. 
5. That it is desirable that the standard scale made some 
years ago by Mr. Troughton for the town of Aberdeen should 
be compared with the standard scale recently made for the 
Royal Astronomical Society, and that Mr. Baily be requested 
to make the requisite comparisons f. 
Desiderata noticed in Mr. Airy's Report , p. 187. 
1. Directions for placing a thermometer so as to indicate cor¬ 
rectly the Temperature of the Air at the place of observation, 
for Refraction-corrections, the external and internal tempera¬ 
tures being supposed as nearly as possible equal. 
2. Experimental Data for the Theory of Refraction— 
What is the law of the decrease of temperature, or of 
density, in ascending ? 
How does this vary at different times ? 
Can any means be contrived for indicating practically at 
different times the modulus of variation ? 
Does the refractive power of air depend simply on its 
density, without regard to its temperature ? 
Is it well established that the effects of moisture are 
almost insensible ? 
Can any rule be given for estimating the effect of the 
difference of refraction in different azimuths, accord¬ 
ing to the form of the ground ? 
When the atmospheric dispersion is considerable, what 
part of the spectrum is it best that Astronomers should 
agree to observe ? 
3. An investigation of the coefficient of Nutation from the 
Greenwich circle-observations. 
* An application lias been made through the Bureau des Longitudes, 
f These comparisons have been made; see p. 91. 
