318 
inventions, stating that he had met with descriptions of several 
in the Philosophical Transactions of the Royal Society, and 
- elsewhere. He then put some questions to Mr Ellis respecting 
the degree of accuracy possible to be attained by such a 
machine. 
Professor MAXWELL described a machine which he had seen 
at the meeting of the British Association this year at Bradford 
for shewing the extent and action of the tides. 
(2) Graphic representation by aid of a series of Hyper- 
bolas of some Economic Problems having reference 
to Monopolies. By Mr A. Marsnatt. 
The price at which a given amount of any commodity can 
be disposed of in any market is determined by the circumstances 
of the buyers. If this amount be measured along Ox and this 
price along Oy, there is thus determined a value of y corre- 
sponding to each value of x; and the locus of the points so 
obtained may be called the demand curve: let its equation be 
y=F (x). Soif y be the price at which an amount @ of the 
commodity can be produced for the market (2, y) is found, the 
locus of which may be called the supply curve: let its equation 
be y=f(x). This method of expressing the problem of value 
has been known certainly for 35 years: an intersection of the 
two curves has been explained as giving the ‘‘average price” 
about which Adam Smith proved that the “market price” will 
oscillate. But it has not been pointed out that, under some 
circumstances, there may be more than one point of intersection, 
and that Adam Smith’s arguments apply only to the circum- 
stances of every alternate pomt. Only at every alternate point 
of intersection can the exchange value remain in stable equili- 
brium: at the other points it is in wastable equilibrium, 
