486 
POPULAR SCIENCE REVIEW. 
Mr. Birt has laid down during the past year, on one sheet, the whole of 
Quadrant IY. (meridians and parallels), 50 in. radius, and inserted Beer and 
Madler’s 23 points of the first order. The greatest error in the position of 
these points is *0008 of the moon’s semi-diameter. The whole of the objects 
on a surface of 15° of longitude and 10° of latitude have been laid down on 
this sheet from the full-moon photograph, and several of them have been 
identified with objects seen conspicuously when near the terminator. A 
portion of this surface, 6° in longitude and 5° in latitude, is completed, and 
enlarged to 100 inches diameter. On it are laid down the positions of 89 
objects, from three independent sets of measures, made on three separate 
photographs, the magnitudes, which are given in the catalogue in seconds of 
an arc, being determined by a separate set of measures. Let us hope that 
ere long the whole moon may thus be sketched, in order that all may be able 
to assist in such an admirable undertaking, and one which is especially fitted 
for amateur work. 
The present progress of the work of reduction of the sun observations taken 
at Kew, will best be gathered from the following extract from a letter 
written by Mr. De La Rue, and printed in the Kew Committee’s Report : — 
“ The pictures taken by means of the Kew heliograph are all measured by 
means of my micrometer ; the positions of the spots are then reduced to dis- 
tances in terms (fractional parts) of the sun’s radius, and the angles of position 
corrected for any error in the position of the wires. Pictures of the pagoda 
are taken from time to time, and the measurements of the various galleries of 
the pagoda serve to determine the optical distortion of the sun’s image and 
the corrections to be applied to the sun-pictures. The heliocentric latitudes 
and longitudes of the spots are then calculated. The areas of the spots and 
the penumbra are also measured, and the areas corrected for perspective are 
tabulated in terms (fractional parts) of the area of the sun’s disk. The areas 
of the spots, &c., on all of Carrington’s original pictures have recently been 
measured, and an account of these measurements will be shortly published.” 
This is good news, although we could wish that the pictures taken by Mr. 
De La Rue’s 13-inch refractor were already in question. 
Our notice of the Association would be incomplete did we not allude to 
Mr. Grove’s admirable discourse, in which astronomic progress is so ably and 
fully discussed, by one who is no mean worker with the telescope. The pre- 
sident’s remarks on the specific gravity of the globe are suggestive enough to 
bear reproduction : — 
“ Surprise has often been expressed that, while the mean specific gravity 
of this globe is from five to six times that of water, the mean specific gravity 
of its crust is barely half as great. It has long seemed to me that there is no 
ground for wonder here. The exterior of our planet is to a considerable 
depth oxidated ; the interior is, in all probability, free from oxygen, and 
whatever bodies exist there are in a reduced or deoxidated state, — if so, their 
specific gravity must necessarily be higher than that of their oxides or 
chlorides, &c. We find, moreover, that some of the deep-seated minerals 
have a higher specific gravity than the average of those on the surface ; 
olivine, for instance, has a specific gravity of 3*3. There is, therefore, no a priori 
improbability that the mean specific gravity of the earth should notably 
exceed that of its surface ; and if we go further, and suppose the interior of 
