‘264 MR. DANIELL ON A NEW REGISTER-PYROMETER 
C C is the lighter arm moving upon the centre f upon the arm B, and carry- 
ing at one end the nonius g, and at the other the steel point h, the distance of 
which from the centre f is exactly half an inch or one-tenth of the radius f g, 
and equal to the distance of the two centres f d. i is a small lens represented 
as lying down, but which may be raised by the centres k and l perpendicularly 
above the nonius to facilitate the reading, m m is the steel spring, which 
being fixed in a cavity cut out of the arm B, presses upon a small pin n on the 
arm C, and throws the radius back to the commencement of the arc. 
Fig. 2. represents the register. DDDD is the black-lead bar, with its 
cavity o o. At p p p p it is cut away to the depth of half the bore, q q is the 
porcelain index, which is placed upon the top of the metallic bar, and confined 
to its place by the pressure of the platinum strap r acting by the force of the 
small porcelain wedge s. 
When an observation is to be made, the metallic bar is placed in the cavity 
of the register, the index is to be pressed down upon it and firmly fixed in its 
place by the platinum strap and porcelain wedge. The scale is then to be ap- 
plied by carefully adjusting the brass rules to the sides of the black-lead bar, 
and fixing it by pressing the cross piece ( a ') upon the shoidder : holding the 
whole together steadily in the left hand, the moveable arm should be so placed 
that the steel point (//) of the other leg of the compasses may rest upon the 
edge of the porcelain index, against which it will be pressed with some force by 
the spring : then moving the arm gently forward with the right hand, the point 
will slide along the end of the index till it drops into a small cavity ( t ) formed 
for its reception, and which exactly coincides with the axis of the metallic bar 
in the register, and the centre of motion of the compasses on the brass rule. 
The minute of the degree must then be noted, which the nonius indicates upon 
the arc. A similar observation must be made after the register has been ex- 
posed to an increased temperature and again cooled ; and the number of 
degrees or minutes which the nonius will then mark will, by a simple calcula- 
tion from the known length of the radii and angle, give the length of the chord 
comprised between the original position of the compasses and the point to 
which they have moved, or the distance which the index has been forced for- 
ward. Such an operation appears complex in the description, but is in fact 
extremely simple after a little practice, and does not require more than a few 
seconds for its performance. The scale of this pyrometer being completely 
