Royal Institute of France. 465 
interval the produce has been more than quadrupled. This work, 
which is 'very important, is accompanied by an interesting map 
which points out the extent of our coal districts, the principal 
pits, and the direction of their various workings. 
M. Vauquelin has again turned his attention to meteoric stones, 
It appears to him that a part of their silex is in combination with 
magnesia: there is also sulphur united to their iron, for it gives 
sulphuretted hydrogen gas on-being dissolved in the acids. As 
to chrome, it seems to be isolated, and it shows itself sometimes 
in molecules so large as to remove every idea of combination, 
Extracts from the Minutes of the Sittings of the Institute of 
March 4, 1816. 
M. Arago made a verbal Report on the Voyage to the South 
Seas, drawn up by M. Louis Freycinet. 
The work is divided into four books: the first bears the title 
of the Itinerary, and makes known the successive order of the 
Operations ; the second comprehends the nautical and geogra-~ 
phical descriptions ; the third is destined to the analysis of charts; 
and the fourth contains the general results of the observations, 
the measurements of inclination and declination of the magnetic 
needle, the remarks of various kinds made during the yoyage, 
and the daily meteorological observations. The whole of the 
voyage is illustrated by thirty-two very fine charts. .M. Frey- 
cinet himself engraved them on copper, and by a process peculiar 
to himself. The chapter in which he describes his method, as 
well as that which relates to the division of the scales, wel] 
merits the attention of engineers, 
M. Biot read a Memoir drawn up by M. Pouillet and himself 
jointly, On the experimental determination of the diffraction 
undergone by simple or compound light when it passes be- 
tween two parallel glass-bottle stoppers. The authors refer to 
measurements of fringes taken at different distances of the bottle 
stoppers on a piece of ground glass ; and by constructing them 
they deduce the mode of separation of the rays, and the definitive 
division which the diffraction impresses upon them, According 
to these measurements, the ribbons which have the least deviated 
have their origin in the points of the interval the nearest to every 
stopper, and the most deviated have their origin nearest the cen- 
tral axis, both being deviated towards the stopper from which 
they were originally the most distant. 
For every given separation of the stoppers, the incidence re- 
maiuing always perpendicular to their interval, the deviations of 
the luminous particles of various natures are proportional to the 
length of their fits in the medium in which the light moves; and 
Vol. 47, No. 218. June 1816. Gg when 
