198 Mr. Daniell on a New Register-Pyrometer^ 



supports upon its bent extremity c, the arm B moving upon 

 the centre d, and terminating in the arc of the circle e e. 



C C is the lighter arm moving upon the cen trey upon the arm 

 B, and carrying at one end the nonius g, and at the other the 

 steel point h, the distance of which from the centrey is exactly 

 half an inch or one-tenth of the radiusy^, and equal to the 

 distance of the two centvesf d. i is a small lens represented 

 as lying down, but which may be raised by the centres k and I 

 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. D D D D is the black-lead 

 bar, with its cavity o o. At ]:> 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 applied 

 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 shoulder : holding the whole together steadily in the left 

 hand, the moveable arm should be so placed that the steel 

 point {h) of the other leg of the compasses may rest upon the 

 ed^e of the porcelain index, against which it will be pressed 

 wiUi 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 miimte 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 

 exposed to an increased temperature and again cooled ; and 

 the number of degrees or minutes which the nonius will then 

 mark will, by a simple calculation 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 forward. 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 



detached 



