58 
stone appeared to be at a right angle to the excavation. 
The place where it occurred was about a quarter of a mile 
to the south of the Old Trafford Kail way Station, opposite 
to some dark-coloured palings on the right-hand side of 
Seymour Grove. 
It is hard to say where the stone came from, but it has 
all the appearance of a fine gritstone of the lower coal 
measures, and great friction may have generated sufficient 
heat to alter its structure in a similar manner to what has 
been done on the sides of great faults and slides where two 
bodies have been rubbed against each other. 
As to its dimensions, we have no data to go upon, except 
the opinion of Mr. Worthington, an experienced judge of 
bulks, and a stone merchant, who, when he first men- 
tioned the specimen to me, said that he estimated its weight 
at over fifty tons. The depth from the surface to the 
bottom of the sewer was thirteen feet. 
“ On the Geometrical Representation of the Equation of 
the Second Degree,” by Charles Chambers, F.RS., Super- 
intendent of the Colaba Observatory, Bombay. Communi- 
cated by J. A. Bennion, F.R.A.S., A.C.RS. 
For every value from — - oo to +oo of one of the variables 
in an equation of the second degree between two variables, 
there are corresponding pairs of values of the other vari- 
able ; and for every value from — -oo to + oo of the second 
variable there are corresponding pairs of values of the first 
variable. The corresponding pairs of values are of two 
classes, viz. first those which are not, and secondly those 
which are, affected by the symbol v/— - 1- The Cartesian 
method gives a perfectly clear geometrical representation 
of that part of the equation for which the values of both 
the variables are real, but discards as unintelligible that 
part for which either of those values is imaginary. In the 
simplest case — of rectangular coordinates — the unit adopted 
