28 REPORT—1857. 
from the first limb by himself, and the second by his assistant, once differed 50”, 
He found the cause of this to be, that the personal equation of the observers differs, 
and unequally, for the two limbs, and both are greater than for stars. The reason 
of this is obvious, for the field round the moon is very dark by contrast, and it is 
not easy to compare a luminous space with a dark one. He found that in fog, 
when the field is nearly as bright as the lunar disc, the longitudes were the most 
consistent, and this led to a mode of illumination which proved effective, and which he 
now mentioned in hope that it might be useful to travellers, as a most effective means 
of getting longitude, if provided with a transit, especially one similar to the “ Broken 
telescope” of Reichenbach’s universal instrument. He placed in front of the object- 
glass a disk of emerald glass, from the centre of which a circle is cut, four-tenths 
of the diameter of the object-glass. This portion forms the image, but the remaining 
portion fills the field with scattered light from the moon, while it contributes none 
to the image. The effect is similar to that of the fog, and it nearly reduces the per- 
sonal error to that of stars. The small aperture, however, gives a larger diameter 
of the moon, and therefore both limbs should be used in nearly equal proportion. 
With these precautions he thought the longitude could be obtained more certainly 
than by any other means within the reach of a traveller, certainly far surpassing the 
ordinary one of lunar distances. = 
On Lunar Physics, 
In a Letter from Professor P. Smyru (o the Assistant General Secretary. 
Royal Observatory, Edinburgh, 
27th August, 1857. 
Dear S1r,—I have to report one more step in the delineation of the moon, 
according to the plan recommended by the British Association, viz. the engraving 
of three views of the Mare Crisium; and I have sent to you, per railway, a parcel 
containing several copies, of which I will request you to lay one before the British 
Association, and to present the others to the officers, as thus :—Rev. Dr. Lloyd, 
President ; Sir W. R. Hamilton, late President ; Rev. Dr. Robinson, late President ; 
General Sabine, Secretary; Prof. Phillips, Assistant Secretary. You will find by 
what I have said on page vi of the pamphlet, that I only look on the present en- 
gravings as a first instalment towards putting our knowledge of this part of the 
moon on a satisfactory footing. Yours very truly, 
C. Prazzi Smytu. 
METEOROLOGY. 
Notice of Meteorological Observations made at Sea. 
Communicated by Rear-Admiral FirzRoy, F.R.S. 
Admiral FitzRoy drew the attention of the Section to the meteorological papers 
lying on the table, which had been recently published by the Board of Trade. The 
Report to which he referred would show what progress had been made, and therefore 
he would not occupy valuable time by entering into verbal details. He would only 
observe generally, that a great number of valuable observations had already been made 
on board some hundred ships, with excellent instruments approved by the Kew Com- 
mittee of the British Association, and that those observations were regularly tabu- 
lated in such a manner as to admit of their being combined in groups or used indi- 
vidually. The willing cooperation of officers at sea had already accumulated more 
observations than can be reduced and tabulated with corresponding quickness ; there- 
fore more reduction of observations, rather than more observers with a larger number 
of instruments, seems necessary; and this can only be accomplished by employing 
a larger staff. The Government had shown the utmost willingness to attend to the 
recommendations of competent authorities with respect to the establishment and 
support of the Meteorological Office at the Board of Trade; and only desired to 
apply the vote sanctioned by Parliament for meteorological observations at sea to the 
best possible advantage. The United States, Great Britain, and Holland, had already 
cooperated largely in this work; and France had lately established a similar depart- 
ment for collecting and discussing such observations, ; 
