8 REPORT—1849., 
and ingenious apparatus executed by that distinguished optician, M. Soleil of Paris, 
and with the aid of a heliostat for fixing the sun-beam in one position during the 
day. The results obtained by Lord Brougham establish a new and interesting pro- 
perty of light, namely, that when a pencil of divergent light has suffered inflection 
by a metallic or any other edge, of any form or substance, it exhibits different pro- 
perties on its different sides when submitted to the action of a second inflecting edge. 
The heliostat being a rare and expensive instrument, and of difficult construction, 
Lord Brougham offered the use of his to any members of the Association who might 
be occupied with experiments on light which required the assistance of it. 
On the Diurnal Variation of Magnetic Declination and the Annual Varia- 
tion of Magnetic Force. By J. A. Broun. 
The details of these results will be found in vol. xix. part 2 of the Transactions 
of the Royal Society of Edinburgh. 
On an Orbitual Motion of the Magnetic Pole round the North Pole of the 
Earth. By the Rev. H. M. Grover, 
This subject was investigated by tracing the positions of the magnetic pole at se- 
veral intervals during the period of the last 250 years, by converging lines drawn 
from the London, Paris and St. Petersburg Observatories, and deduced by compu- 
tations of the different variations of the magnetic needle at these places. These 
changes were shown very distinctly upon the different polar horizons of the obser- 
vatories, and the orbit drawn from them in its proper position. An extraordinary 
acceleration of this motion from 1580 down to 1723 was pointed out, and a pause 
at that period, which indicated a climax in that year, in which both the horizontal 
movement of the needle was suspended, and the dipping motion changed its course 
from a downward to an upward motion. Mr. Grover showed also a series of changes 
in the lines of equal dectination about the isodynamic poles, which appeared to in- 
dicate a direct tendency, or attractive force operating upon the magnetic needles 
from those poles, which he assumed and showed to be sufficient to account for the 
extra linear position of the line of no declination between Europe and Asia, as well 
as for the extraordinary curvatures of the declination lines observed in the north of 
Asia on the two sides of the isodynamic pole, and the origin and changes of the 
closed systems or ovals in their Asiatic and Pacific allocations. Mr. Grover regarded 
the moving magnetic pole in the light of a satellite, or supplemental system, to the 
isogonal poles, disturbed by the accumulations of ice about the pole in the course of 
a long series of ages, and generated as a compensative process from an interruption 
of the original system. 
On some recent Discussions relative to the Theory of the Dispersion of Light. 
By the Rev. Prof. Power, F.R.S, &e. 
Two eminent continental writers have recently published some discussions on this 
subject, which seem to call for a few brief remarks. 
M. Mossotti, in a memoir ‘ On the Spectrum of Fraunhofer,’”’ &c. (Paris, 1845, 
transl. in Taylor’s Foreign Scientific Memoirs, No. xix. p. 435), compares the in- 
terference or grating spectrum, with that formed by refraction, as to the intensity of 
light at its different parts, and the relation of the deviation to the values of A, the 
wave length, which in the former is simple and norma). 
As to any measures of the intensity of light at different parts of the spectrum, it 
appears to be a necessary condition to state the kind or degree of light used, whe- 
ther the full solar rays, or bright or dull daylight ; since in the former case the inten- 
sity of the middle part of the spectrum enormously exceeds and overpowers that of 
every other part, while in the latter cases it is only in a slight degree brighter. 
In Part II. § 2, the author gives the dispersion formula substantially thesame as 
M. Cauchy’s, as far as the 4th power of A. He adopts a method of calculation by 
means of least squares, and considers the verification sufficient, from the agreement 
in one specimen of Fraunhofer’s flint-glass. 
It cannot but excite surprise to find so eminent a philosopher at the present day 

