1863.] Mr. Glaisher on the Storm of October SO, 1863. 19 



He then institutes a comparison between the results afforded by those 

 three of the eight arcs which are of considerable extent, namely, the Anglo- 

 Gallic, Russian, and Indian Arcs. For each arc in particular he deduces 

 values of the principal semiaxes of the earth, involving an unknown con- 

 stant expressing the effect of local attraction at the reference station of the 

 arc. In order that the three pairs of semiaxes should agree, there are 

 four equations to be satisfied by means of three disposable quantities 

 (namely, the three unknown attractions). On combining these four equa- 

 tions by the method of least squares, the unknown deflections come out 

 extremely small, and the values of each semiaxis deduced for the three arcs 

 separately come out very nearly equal to one another, and therefore to their 

 mean. These mean values the author ventures to assume are the mean 

 semiaxes of the earth. They are as follows : — 



a = 20926180, 5=20855316 feet, giving e=^y 

 where a is the equatorial, and b the polar semiaxis, and e the ellipticity. 



The author concludes with certain speculations respecting the constitution 

 of the earth's crust. On adopting the mean figure determined as above 

 explained, the errors of latitude to be attributed to local attraction at each 

 of the fifty-five stations of the eight arcs, which will be found at p. 766 of 

 the Ordnance Survey volume, come out very small. With respect to the 

 Great Indian Arc, it is especially remarkable that the residual deflections 

 are insignificant, while those calculated from the action of the causes visibly 

 at work are considerable. It would seem as if some general cause were at 

 work to increase the density under the ocean, and diminish the density under 

 mountainous tracts of country. The author conceives that, as the earth 

 cooled down from a state of fusion sufficiently to allow a permanent crust 

 to be formed, those regions where the crust contracted became basins into 

 which the waters ran, while regions where expansion accompanied solidifi- 

 cation became elevated without any consequent increase in the total quantity 

 of matter in a vertical column extending from the surface down to a given 

 surface of equal pressure in the yet viscous mass below. The author 

 considers that the deviations of latitude at the other principal stations of 

 the measured arcs, if not positively confirmatory of, are at least not opposed 

 to this view. 



IV. "On the Meteorological Results shown by the Self-registering 

 Instruments at Greenwich during the extraordinary Storm of 

 October 30, 1863." By James Glaisher, F.R.S., F.R.A.S., &c. 

 Received November 23, 1863. 



In the year 1841 Osier's anemometer was erected at the Royal Obser- 

 vatory, Greenwich, and from that time, up to the year 1860, the greatest 

 pressure on the square foot recorded was 25 lbs. In February 1860 one 

 of 28 lbs. was registered, which was the greatest up to October 30 of the 

 present year ; on that day a pressure of no less than 29|^lbs. took place 



c2 



