Dr. Fordyce's Account of a new Pendulum. 3 
rods AB, DC, be shortened by exposure to cold ; so that in all 
cases of heat or cold the end of the rod CD at D, and the end 
of the rod BA at A, shall be in a line parallel to the horizon. 
Take a point E near any part of the rod CD, and let that 
point E be connected with the point A, where the end A of 
the rod AB is fixed, and let the matter which unites them be 
perfectly inflexible, and incapable of being altered by heat ; 
then, I say, that the part of the rod CD, intercepted at the 
point E, and forming ED, will always be of the same length 
whether the temperature of heat is greater or less. For sup- 
posing a point F be taken near the rod AB, and of the same 
perpendicular height with E, so that a line drawn from E to 1 
F shall be parallel to the horizon ; if the part of the rod AB, 
opposite to F, should rise up in consequence of being expanded 
by heat above F, it will carry up the point of the rod DC, 
which was opposite to E, to an equal height with itself, and 
therefore would cut off from the length of that part of the rod 
which was formerly opposite to E, a length equal to that which 
was added to what was formerly ED, by the heat. Therefore 
the point opposite to E, in the rod DC, will form ED, which 
will always continue of the same length, if the heat be in- 
creased ; and by similar reasoning, it will likewise continue of 
the same length if the part of the rod AB AF is shortened by 
cold ; therefore the part of the rod DC cut off by the point E, 
so as to form ED, will always be of an equal length, and the 
point D will always be of an equal height. 
At the point E let there be an apparatus which will render 
that part of the rod DC which is opposite to the point E 
flexible, whatever part of it shall be opposite to the point E 
Then the part of the rod DC, cut off at the point E, and form- 
