17 
approaching to this magnificent display has occurred here 
for very many years. 
Mr. Baxendell stated that his observations of the 
Aurora of the 25 th ult. were directed principally to the 
determination of the position of the centre of the corona, 
or point to which the beams of the Aurora appeared to 
converge, by reference to the stars in its immediate neigh- 
bourhood. The mean of his results gave at Gh. 35m. G.M.T. 
azimuth, S. 19° 52' E ; altitude, 66° 9'. From this position 
it would appear that the direction of the lines of magnetic 
force in the region of the auroral beams deviated sensibly 
from parallelism with the line of dip at the surface of the 
earth. 
Mr. Boyd Dawkins, F.B.S., exhibited a number of casts in 
plaster of Paris of various objects of natural history, and ex- 
plained the process by which any one can make them for him- 
self. The material of the mould is artists’ modelling wax, 
which is a composition akin to that which is used by dentists. 
And as it becomes soft and plastic by the application of heat, 
though in a cold state it is perfectly rigid, it may be applied 
to the most delicate object without injury. As it takes the 
most minute markings and striations of the original to which 
it is applied, the microscopic structure of the surface of the 
original is faithfully reproduced in the cast. The method is 
briefly this. 1. Cover the object to be cast with a thin 
powder of steatite or French chalk, which prevents the 
adhesion of the wax. 2. After the wax has become soft 
either from immersion in warm water or from exposure to 
the direct heat of the fire, apply it to the original, being 
careful to press it into the little cavities. Then carefully 
cut off the edges of the wax all round, if the under cutting 
of the object necessitates the mould being in two or more 
pieces, and let the wax cool with the object in it, until it be 
sufficiently hard to bear the repetition of the operation on 
